Fungus

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Fungi
Temporal range: Early DevonianPresent (but see text) 410–0  Ma
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Scientific classification Red Pencil Icon.png
(unranked): Opisthokonta
(unranked): Holomycota
(unranked): Zoosporia
Kingdom:Fungi
(L.) R.T.Moore [1]
Subkingdoms/Phyla/Subphyla [2]
Blastocladiomycota
Chytridiomycota
Glomeromycota
Microsporidia
Neocallimastigomycota

Dikarya (inc. Deuteromycota)

Ascomycota
Pezizomycotina
Saccharomycotina
Taphrinomycotina
Basidiomycota
Agaricomycotina
Pucciniomycotina
Ustilaginomycotina

Subphyla incertae sedis

Entomophthoromycotina
Kickxellomycotina
Mucoromycotina
Zoopagomycotina

A fungus (plural: fungi [3] or funguses [4] ) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, fungi, which is separate from the other eukaryotic life kingdoms of plants and animals.

The plural, in many languages, is one of the values of the grammatical category of number. Plural of nouns typically denote a quantity other than the default quantity represented by a noun, which is generally one. Most commonly, therefore, plurals are used to denote two or more of something, although they may also denote more than fractional, zero or negative amounts. An example of a plural is the English word cats, which corresponds to the singular cat.

Eukaryote Taxonomic group whose members have complex structures enclosed within membranes

Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, unlike prokaryotes, which have no membrane-bound organelles. Eukaryotes belong to the domain Eukaryota or Eukarya. Their name comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, and in addition, some cells of plants and algae contain chloroplasts. Unlike unicellular archaea and bacteria, eukaryotes may also be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Animals and plants are the most familiar eukaryotes.

Yeast Informal group of fungi

Yeasts are eukaryotic single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and 1,500 species are currently identified. They are estimated to constitute 1% of all described fungal species. Yeasts are unicellular organisms that evolved from multicellular ancestors, with some species having the ability to develop multicellular characteristics by forming strings of connected budding cells known as pseudohyphae or false hyphae. Yeast sizes vary greatly, depending on species and environment, typically measuring 3–4 µm in diameter, although some yeasts can grow to 40 µm in size. Most yeasts reproduce asexually by mitosis, and many do so by the asymmetric division process known as budding.

Contents

A characteristic that places fungi in a different kingdom from plants, bacteria, and some protists is chitin in their cell walls. Similar to animals, fungi are heterotrophs; they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Fungi do not photosynthesize. Growth is their means of mobility, except for spores (a few of which are flagellated), which may travel through the air or water. Fungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the Eumycota (true fungi or Eumycetes), which share a common ancestor (form a monophyletic group), an interpretation that is also strongly supported by molecular phylogenetics. This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek μύκης mykes, mushroom). In the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more closely related to animals than to plants.

Chitin long-chain polymer of a N-acetylglucosamine

Chitin (C8H13O5N)n ( KY-tin), a long-chain polymer of N-acetylglucosamine, is a derivative of glucose. It is a primary component of cell walls in fungi, the exoskeletons of arthropods, such as crustaceans and insects, the radulae of molluscs, cephalopod beaks, and the scales of fish and lissamphibians. The structure of chitin is comparable to another polysaccharide—cellulose, forming crystalline nanofibrils or whiskers. In terms of function, it may be compared to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.

Cell wall rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, most prokaryotic cells and some protozoan parasites, maintaining their shape and protecting them from osmotic lysis

A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, fungi and eukaryotes including plants but are absent in animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters.

Heterotroph organism that ingests or absorbs organic carbon (rather than fix carbon from inorganic sources such as carbon dioxide) in order to be able to produce energy and synthesize compounds to maintain its life

A heterotroph is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Living organisms that are heterotrophic include all animals and fungi, some bacteria and protists, and parasitic plants. The term heterotroph arose in microbiology in 1946 as part of a classification of microorganisms based on their type of nutrition. The term is now used in many fields, such as ecology in describing the food chain.

Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil or on dead matter. Fungi include symbionts of plants, animals, or other fungi and also parasites. They may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. They have long been used as a direct source of human food, in the form of mushrooms and truffles; as a leavening agent for bread; and in the fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g., rice blast disease) or food spoilage can have a large impact on human food supplies and local economies.

Crypsis ability of an organism to avoid observation, detection

In ecology, crypsis is the ability of an animal to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and mimicry. Crypsis can involve visual, olfactory, or auditory concealment. When it is visual, the term cryptic coloration, effectively a synonym for animal camouflage, is sometimes used, but many different methods of camouflage are employed by animals.

Symbiosis type of a close and long-term biological interaction between two different biological organisms

Symbiosis is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic. The organisms, each termed a symbiont, may be of the same or of different species. In 1879, Heinrich Anton de Bary defined it as "the living together of unlike organisms". The term was subject to a century-long debate about whether it should specifically denote mutualism, as in lichens; biologists have now abandoned that restriction.

Sporocarp (fungi) multicellular structure on which spore-producing structures (basidia or asci) are borne; part of the sexual phase of a fungal life cycle, with the rest of the life cycle being characterized by vegetative mycelial growth and asexual spore production

In fungi, the sporocarp is a multicellular structure on which spore-producing structures, such as basidia or asci, are born. The fruitbody is part of the sexual phase of a fungal life cycle, while the rest of the life cycle is characterized by vegetative mycelial growth and asexual spore production.

The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, and morphologies ranging from unicellular aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of Kingdom Fungi, which has been estimated at 2.2 million to 3.8 million species. [5] Of these, only about 120,000 have been described, with over 8,000 species known to be detrimental to plants and at least 300 that can be pathogenic to humans. [6] Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, and Elias Magnus Fries, fungi have been classified according to their morphology (e.g., characteristics such as spore color or microscopic features) or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits. Phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla.

Taxon Group of one or more populations of an organism or organisms which have distinguishing characteristics in common

In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Biological life cycle period involving all different generations of a species succeeding each other through means of reproduction

In biology, a biological life cycle is a series of changes in form that an organism undergoes, returning to the starting state. "The concept is closely related to those of the life history, development and ontogeny, but differs from them in stressing renewal." Transitions of form may involve growth, asexual reproduction, or sexual reproduction.

Morphology (biology) In biology, the form and structure of organisms

Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features.

Etymology

The English word fungus is directly adopted from the Latin fungus (mushroom), used in the writings of Horace and Pliny. [7] This in turn is derived from the Greek word sphongos (σφόγγος "sponge"), which refers to the macroscopic structures and morphology of mushrooms and molds; [8] the root is also used in other languages, such as the German Schwamm ("sponge") and Schimmel ("mold"). [9]

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets and ultimately from the Phoenician alphabet.

Horace Roman lyric poet

Quintus Horatius Flaccus, known in the English-speaking world as Horace, was the leading Roman lyric poet during the time of Augustus. The rhetorician Quintilian regarded his Odes as just about the only Latin lyrics worth reading: "He can be lofty sometimes, yet he is also full of charm and grace, versatile in his figures, and felicitously daring in his choice of words."

Pliny the Elder Roman military commander and writer

Pliny the Elder was a Roman author, a naturalist and natural philosopher, a naval and army commander of the early Roman Empire, and a friend of emperor Vespasian.

The word mycology is derived from the Greek mykes (μύκης "mushroom") and logos (λόγος "discourse"). [10] It denotes the scientific study of fungi. The Latin adjectival form of "mycology" (mycologicæ) appeared as early as 1796 in a book on the subject by Christiaan Hendrik Persoon. [11] The word appeared in English as early as 1824 in a book by Robert Kaye Greville. [12] In 1836 the English naturalist Miles Joseph Berkeley's publication The English Flora of Sir James Edward Smith, Vol. 5. also refers to mycology as the study of fungi. [8] [13]

Christiaan Hendrik Persoon mycologist who made additions to Linnaeus mushroom taxonomy

Christiaan Hendrik Persoon was a mycologist who made additions to Linnaeus' mushroom taxonomy.

Robert Kaye Greville British botanist (1794-1866)

Dr Robert Kaye Greville FRSE FLS LLD was an English mycologist, bryologist, and botanist. He was an accomplished artist and illustrator of natural history. In addition to art and science he was interested in causes like abolitionism, capital punishment, keeping Sunday special and the temperance movement. He has a mountain in Queensland named after him.

Miles Joseph Berkeley British botanist

Miles Joseph Berkeley was an English cryptogamist and clergyman, and one of the founders of the science of plant pathology. The standard author abbreviation Berk. is used to indicate this person as the author when citing a botanical name.

A group of all the fungi present in a particular area or geographic region is known as mycobiota (plural noun, no singular), e.g., "the mycobiota of Ireland". [14]

Characteristics

Fungal hyphae cells
Hyphal wall
Septum
Mitochondrion
Vacuole
Ergosterol crystal
Ribosome
Nucleus
Endoplasmic reticulum
Lipid body
Plasma membrane
Spitzenkorper
Golgi apparatus HYPHAE.png
Fungal hyphae cells

Before the introduction of molecular methods for phylogenetic analysis, taxonomists considered fungi to be members of the plant kingdom because of similarities in lifestyle: both fungi and plants are mainly immobile, and have similarities in general morphology and growth habitat. Like plants, fungi often grow in soil and, in the case of mushrooms, form conspicuous fruit bodies, which sometimes resemble plants such as mosses. The fungi are now considered a separate kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago (around the start of the Neoproterozoic Era). [15] [16] Some morphological, biochemical, and genetic features are shared with other organisms, while others are unique to the fungi, clearly separating them from the other kingdoms:

Shared features:

Unique features:

Omphalotus nidiformis, a bioluminescent mushroom Omphalotus nidiformis Binnamittalong 2 email.jpg
Omphalotus nidiformis , a bioluminescent mushroom

Most fungi lack an efficient system for the long-distance transport of water and nutrients, such as the xylem and phloem in many plants. To overcome this limitation, some fungi, such as Armillaria , form rhizomorphs, [32] which resemble and perform functions similar to the roots of plants. As eukaryotes, fungi possess a biosynthetic pathway for producing terpenes that uses mevalonic acid and pyrophosphate as chemical building blocks. [33] Plants and some other organisms have an additional terpene biosynthesis pathway in their chloroplasts, a structure fungi and animals do not have. [34] Fungi produce several secondary metabolites that are similar or identical in structure to those made by plants. [33] Many of the plant and fungal enzymes that make these compounds differ from each other in sequence and other characteristics, which indicates separate origins and convergent evolution of these enzymes in the fungi and plants. [33] [35]

Diversity

Bracket fungi on a tree stump Fungus in a Wood.JPG
Bracket fungi on a tree stump

Fungi have a worldwide distribution, and grow in a wide range of habitats, including extreme environments such as deserts or areas with high salt concentrations [36] or ionizing radiation, [37] as well as in deep sea sediments. [38] Some can survive the intense UV and cosmic radiation encountered during space travel. [39] Most grow in terrestrial environments, though several species live partly or solely in aquatic habitats, such as the chytrid fungus Batrachochytrium dendrobatidis , a parasite that has been responsible for a worldwide decline in amphibian populations. This organism spends part of its life cycle as a motile zoospore, enabling it to propel itself through water and enter its amphibian host. [40] Other examples of aquatic fungi include those living in hydrothermal areas of the ocean. [41]

Around 120,000 species of fungi have been described by taxonomists, [42] but the global biodiversity of the fungus kingdom is not fully understood. [42] A 2017 estimate suggests there may be between 2.2 and 3.8 million species. [5] In mycology, species have historically been distinguished by a variety of methods and concepts. Classification based on morphological characteristics, such as the size and shape of spores or fruiting structures, has traditionally dominated fungal taxonomy. [43] Species may also be distinguished by their biochemical and physiological characteristics, such as their ability to metabolize certain biochemicals, or their reaction to chemical tests. The biological species concept discriminates species based on their ability to mate. The application of molecular tools, such as DNA sequencing and phylogenetic analysis, to study diversity has greatly enhanced the resolution and added robustness to estimates of genetic diversity within various taxonomic groups. [44]

Mycology

Mycology is the branch of biology concerned with the systematic study of fungi, including their genetic and biochemical properties, their taxonomy, and their use to humans as a source of medicine, food, and psychotropic substances consumed for religious purposes, as well as their dangers, such as poisoning or infection. The field of phytopathology, the study of plant diseases, is closely related because many plant pathogens are fungi. [45]

In 1729, Pier Antonio Micheli first published descriptions of fungi. Pier Antonio Micheli.jpg
In 1729, Pier Antonio Micheli first published descriptions of fungi.

The use of fungi by humans dates back to prehistory; Ötzi the Iceman, a well-preserved mummy of a 5,300-year-old Neolithic man found frozen in the Austrian Alps, carried two species of polypore mushrooms that may have been used as tinder ( Fomes fomentarius ), or for medicinal purposes ( Piptoporus betulinus ). [46] Ancient peoples have used fungi as food sources–often unknowingly–for millennia, in the preparation of leavened bread and fermented juices. Some of the oldest written records contain references to the destruction of crops that were probably caused by pathogenic fungi. [47]

History

Mycology is a relatively new science that became systematic after the development of the microscope in the 17th century. Although fungal spores were first observed by Giambattista della Porta in 1588, the seminal work in the development of mycology is considered to be the publication of Pier Antonio Micheli's 1729 work Nova plantarum genera. [48] Micheli not only observed spores but also showed that, under the proper conditions, they could be induced into growing into the same species of fungi from which they originated. [49] Extending the use of the binomial system of nomenclature introduced by Carl Linnaeus in his Species plantarum (1753), the Dutch Christian Hendrik Persoon (1761–1836) established the first classification of mushrooms with such skill as to be considered a founder of modern mycology. Later, Elias Magnus Fries (1794–1878) further elaborated the classification of fungi, using spore color and microscopic characteristics, methods still used by taxonomists today. Other notable early contributors to mycology in the 17th–19th and early 20th centuries include Miles Joseph Berkeley, August Carl Joseph Corda, Anton de Bary, the brothers Louis René and Charles Tulasne, Arthur H. R. Buller, Curtis G. Lloyd, and Pier Andrea Saccardo. The 20th century has seen a modernization of mycology that has come from advances in biochemistry, genetics, molecular biology, and biotechnology. The use of DNA sequencing technologies and phylogenetic analysis has provided new insights into fungal relationships and biodiversity, and has challenged traditional morphology-based groupings in fungal taxonomy. [50]

Morphology

Microscopic structures

An environmental isolate of Penicillium
hypha
conidiophore
phialide
conidia
septa Penicillium labeled cropped.jpg
An environmental isolate of Penicillium

Most fungi grow as hyphae, which are cylindrical, thread-like structures 2–10  µm in diameter and up to several centimeters in length. Hyphae grow at their tips (apices); new hyphae are typically formed by emergence of new tips along existing hyphae by a process called branching, or occasionally growing hyphal tips fork, giving rise to two parallel-growing hyphae. [51] Hyphae also sometimes fuse when they come into contact, a process called hyphal fusion (or anastomosis). These growth processes lead to the development of a mycelium, an interconnected network of hyphae. [27] Hyphae can be either septate or coenocytic. Septate hyphae are divided into compartments separated by cross walls (internal cell walls, called septa, that are formed at right angles to the cell wall giving the hypha its shape), with each compartment containing one or more nuclei; coenocytic hyphae are not compartmentalized. [52] Septa have pores that allow cytoplasm, organelles, and sometimes nuclei to pass through; an example is the dolipore septum in fungi of the phylum Basidiomycota. [53] Coenocytic hyphae are in essence multinucleate supercells. [54]

Many species have developed specialized hyphal structures for nutrient uptake from living hosts; examples include haustoria in plant-parasitic species of most fungal phyla, and arbuscules of several mycorrhizal fungi, which penetrate into the host cells to consume nutrients. [55]

Although fungi are opisthokonts—a grouping of evolutionarily related organisms broadly characterized by a single posterior flagellum—all phyla except for the chytrids have lost their posterior flagella. [56] Fungi are unusual among the eukaryotes in having a cell wall that, in addition to glucans (e.g., β-1,3-glucan) and other typical components, also contains the biopolymer chitin. [57]

Macroscopic structures

Armillaria solidipes Armillaria ostoyae MO.jpg
Armillaria solidipes

Fungal mycelia can become visible to the naked eye, for example, on various surfaces and substrates, such as damp walls and spoiled food, where they are commonly called molds. Mycelia grown on solid agar media in laboratory petri dishes are usually referred to as colonies. These colonies can exhibit growth shapes and colors (due to spores or pigmentation) that can be used as diagnostic features in the identification of species or groups. [58] Some individual fungal colonies can reach extraordinary dimensions and ages as in the case of a clonal colony of Armillaria solidipes , which extends over an area of more than 900  ha (3.5 square miles), with an estimated age of nearly 9,000 years. [59]

The apothecium—a specialized structure important in sexual reproduction in the ascomycetes—is a cup-shaped fruit body that is often macroscopic and holds the hymenium, a layer of tissue containing the spore-bearing cells. [60] The fruit bodies of the basidiomycetes (basidiocarps) and some ascomycetes can sometimes grow very large, and many are well known as mushrooms.

Growth and physiology

Mold growth covering a decaying peach. The frames were taken approximately 12 hours apart over a period of six days. DecayingPeachSmall.gif
Mold growth covering a decaying peach. The frames were taken approximately 12 hours apart over a period of six days.

The growth of fungi as hyphae on or in solid substrates or as single cells in aquatic environments is adapted for the efficient extraction of nutrients, because these growth forms have high surface area to volume ratios. [61] Hyphae are specifically adapted for growth on solid surfaces, and to invade substrates and tissues. [62] They can exert large penetrative mechanical forces; for example, many plant pathogens, including Magnaporthe grisea , form a structure called an appressorium that evolved to puncture plant tissues. [63] The pressure generated by the appressorium, directed against the plant epidermis, can exceed 8 megapascals (1,200 psi). [63] The filamentous fungus Paecilomyces lilacinus uses a similar structure to penetrate the eggs of nematodes. [64]

The mechanical pressure exerted by the appressorium is generated from physiological processes that increase intracellular turgor by producing osmolytes such as glycerol. [65] Adaptations such as these are complemented by hydrolytic enzymes secreted into the environment to digest large organic molecules—such as polysaccharides, proteins, and lipids—into smaller molecules that may then be absorbed as nutrients. [66] [67] [68] The vast majority of filamentous fungi grow in a polar fashion (extending in one direction) by elongation at the tip (apex) of the hypha. [69] Other forms of fungal growth include intercalary extension (longitudinal expansion of hyphal compartments that are below the apex) as in the case of some endophytic fungi, [70] or growth by volume expansion during the development of mushroom stipes and other large organs. [71] Growth of fungi as multicellular structures consisting of somatic and reproductive cells—a feature independently evolved in animals and plants [72] —has several functions, including the development of fruit bodies for dissemination of sexual spores (see above) and biofilms for substrate colonization and intercellular communication. [73]

The fungi are traditionally considered heterotrophs, organisms that rely solely on carbon fixed by other organisms for metabolism. Fungi have evolved a high degree of metabolic versatility that allows them to use a diverse range of organic substrates for growth, including simple compounds such as nitrate, ammonia, acetate, or ethanol. [74] [75] In some species the pigment melanin may play a role in extracting energy from ionizing radiation, such as gamma radiation. This form of "radiotrophic" growth has been described for only a few species, the effects on growth rates are small, and the underlying biophysical and biochemical processes are not well known. [37] This process might bear similarity to CO2 fixation via visible light, but instead uses ionizing radiation as a source of energy. [76]

Reproduction

Polyporus squamosus Polyporus squamosus Molter.jpg
Polyporus squamosus

Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms. [77] It is estimated that a third of all fungi reproduce using more than one method of propagation; for example, reproduction may occur in two well-differentiated stages within the life cycle of a species, the teleomorph and the anamorph. [78] Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containing propagules.

Asexual reproduction

Asexual reproduction occurs via vegetative spores (conidia) or through mycelial fragmentation. Mycelial fragmentation occurs when a fungal mycelium separates into pieces, and each component grows into a separate mycelium. Mycelial fragmentation and vegetative spores maintain clonal populations adapted to a specific niche, and allow more rapid dispersal than sexual reproduction. [79] The "Fungi imperfecti" (fungi lacking the perfect or sexual stage) or Deuteromycota comprise all the species that lack an observable sexual cycle. [80] Deuteromycota is not an accepted taxonomic clade, and is now taken to mean simply fungi that lack a known sexual stage.

Sexual reproduction

Sexual reproduction with meiosis has been directly observed in all fungal phyla except Glomeromycota [81] (genetic analysis suggests meiosis in Glomeromycota as well). It differs in many aspects from sexual reproduction in animals or plants. Differences also exist between fungal groups and can be used to discriminate species by morphological differences in sexual structures and reproductive strategies. [82] [83] Mating experiments between fungal isolates may identify species on the basis of biological species concepts. [83] The major fungal groupings have initially been delineated based on the morphology of their sexual structures and spores; for example, the spore-containing structures, asci and basidia, can be used in the identification of ascomycetes and basidiomycetes, respectively. Fungi employ two mating systems: heterothallic species allow mating only between individuals of opposite mating type, whereas homothallic species can mate, and sexually reproduce, with any other individual or itself. [84]

Most fungi have both a haploid and a diploid stage in their life cycles. In sexually reproducing fungi, compatible individuals may combine by fusing their hyphae together into an interconnected network; this process, anastomosis, is required for the initiation of the sexual cycle. Many ascomycetes and basidiomycetes go through a dikaryotic stage, in which the nuclei inherited from the two parents do not combine immediately after cell fusion, but remain separate in the hyphal cells (see heterokaryosis). [85]

The 8-spore asci of Morchella elata, viewed with phase contrast microscopy Morelasci.jpg
The 8-spore asci of Morchella elata , viewed with phase contrast microscopy

In ascomycetes, dikaryotic hyphae of the hymenium (the spore-bearing tissue layer) form a characteristic hook at the hyphal septum. During cell division, formation of the hook ensures proper distribution of the newly divided nuclei into the apical and basal hyphal compartments. An ascus (plural asci) is then formed, in which karyogamy (nuclear fusion) occurs. Asci are embedded in an ascocarp, or fruiting body. Karyogamy in the asci is followed immediately by meiosis and the production of ascospores. After dispersal, the ascospores may germinate and form a new haploid mycelium. [86]

Sexual reproduction in basidiomycetes is similar to that of the ascomycetes. Compatible haploid hyphae fuse to produce a dikaryotic mycelium. However, the dikaryotic phase is more extensive in the basidiomycetes, often also present in the vegetatively growing mycelium. A specialized anatomical structure, called a clamp connection, is formed at each hyphal septum. As with the structurally similar hook in the ascomycetes, the clamp connection in the basidiomycetes is required for controlled transfer of nuclei during cell division, to maintain the dikaryotic stage with two genetically different nuclei in each hyphal compartment. [87] A basidiocarp is formed in which club-like structures known as basidia generate haploid basidiospores after karyogamy and meiosis. [88] The most commonly known basidiocarps are mushrooms, but they may also take other forms (see Morphology section).

In fungi formerly classified as Zygomycota, haploid hyphae of two individuals fuse, forming a gametangium, a specialized cell structure that becomes a fertile gamete-producing cell. The gametangium develops into a zygospore, a thick-walled spore formed by the union of gametes. When the zygospore germinates, it undergoes meiosis, generating new haploid hyphae, which may then form asexual sporangiospores. These sporangiospores allow the fungus to rapidly disperse and germinate into new genetically identical haploid fungal mycelia. [89]

Spore dispersal

Both asexual and sexual spores or sporangiospores are often actively dispersed by forcible ejection from their reproductive structures. This ejection ensures exit of the spores from the reproductive structures as well as traveling through the air over long distances.

The bird's nest fungus Cyathus stercoreus Cyathus stercoreus Fruchtkorper.JPG
The bird's nest fungus Cyathus stercoreus

Specialized mechanical and physiological mechanisms, as well as spore surface structures (such as hydrophobins), enable efficient spore ejection. [90] For example, the structure of the spore-bearing cells in some ascomycete species is such that the buildup of substances affecting cell volume and fluid balance enables the explosive discharge of spores into the air. [91] The forcible discharge of single spores termed ballistospores involves formation of a small drop of water (Buller's drop), which upon contact with the spore leads to its projectile release with an initial acceleration of more than 10,000  g; [92] the net result is that the spore is ejected 0.01–0.02 cm, sufficient distance for it to fall through the gills or pores into the air below. [93] Other fungi, like the puffballs, rely on alternative mechanisms for spore release, such as external mechanical forces. The bird's nest fungi use the force of falling water drops to liberate the spores from cup-shaped fruiting bodies. [94] Another strategy is seen in the stinkhorns, a group of fungi with lively colors and putrid odor that attract insects to disperse their spores. [95]

The most common means of spore dispersal is by wind - species using this form of dispersal often produce dry or hydrophobic spores which do not absorb water and are readily scattered by raindrops, for example. Most of the researched species of fungus are transported by wind. [96] [97]

Homothallism

In homothallic sexual reproduction, two haploid nuclei derived from the same individual fuse to form a zygote that can then undergo meiosis. Homothallic fungi include species with an aspergillus-like asexual stage (anamorphs) occurring in numerous different genera, [98] several species of the ascomycete genus Cochliobolus , [99] and the ascomycete Pneumocystis jiroveccii. [100] Heitman [101] reviewed evidence bearing on the evolution of sexual reproduction in the fungi and concluded that the earliest mode of sexual reproduction among eukaryotes was likely homothallism, that is, self-fertile unisexual reproduction.

Other sexual processes

Besides regular sexual reproduction with meiosis, certain fungi, such as those in the genera Penicillium and Aspergillus , may exchange genetic material via parasexual processes, initiated by anastomosis between hyphae and plasmogamy of fungal cells. [102] The frequency and relative importance of parasexual events is unclear and may be lower than other sexual processes. It is known to play a role in intraspecific hybridization [103] and is likely required for hybridization between species, which has been associated with major events in fungal evolution. [104]

Evolution

In contrast to plants and animals, the early fossil record of the fungi is meager. Factors that likely contribute to the under-representation of fungal species among fossils include the nature of fungal fruiting bodies, which are soft, fleshy, and easily degradable tissues and the microscopic dimensions of most fungal structures, which therefore are not readily evident. Fungal fossils are difficult to distinguish from those of other microbes, and are most easily identified when they resemble extant fungi. [105] Often recovered from a permineralized plant or animal host, these samples are typically studied by making thin-section preparations that can be examined with light microscopy or transmission electron microscopy. [106] Researchers study compression fossils by dissolving the surrounding matrix with acid and then using light or scanning electron microscopy to examine surface details. [107]

The earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some 2,400  million years ago (Ma); these multicellular benthic organisms had filamentous structures capable of anastomosis. [108] Other studies (2009) estimate the arrival of fungal organisms at about 760–1060 Ma on the basis of comparisons of the rate of evolution in closely related groups. [109] For much of the Paleozoic Era (542–251 Ma), the fungi appear to have been aquatic and consisted of organisms similar to the extant chytrids in having flagellum-bearing spores. [110] The evolutionary adaptation from an aquatic to a terrestrial lifestyle necessitated a diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships such as mycorrhiza and lichenization. [111] Recent (2009) studies suggest that the ancestral ecological state of the Ascomycota was saprobism, and that independent lichenization events have occurred multiple times. [112]

In May 2019, scientists reported the discovery of a fossilized fungus, named Ourasphaira giraldae , in the Canadian Arctic, that may have grown on land a billion years ago, well before plants were living on land. [113] [114] [115] Earlier, it had been presumed that the fungi colonized the land during the Cambrian (542–488.3 Ma), also long before land plants. [116] Fossilized hyphae and spores recovered from the Ordovician of Wisconsin (460 Ma) resemble modern-day Glomerales, and existed at a time when the land flora likely consisted of only non-vascular bryophyte-like plants. [117] Prototaxites, which was probably a fungus or lichen, would have been the tallest organism of the late Silurian. Fungal fossils do not become common and uncontroversial until the early Devonian (416–359.2 Ma), when they occur abundantly in the Rhynie chert, mostly as Zygomycota and Chytridiomycota. [116] [118] [119] At about this same time, approximately 400 Ma, the Ascomycota and Basidiomycota diverged, [120] and all modern classes of fungi were present by the Late Carboniferous (Pennsylvanian, 318.1–299 Ma). [121]

Lichen-like fossils have been found in the Doushantuo Formation in southern China dating back to 635–551 Ma. [122] Lichens formed a component of the early terrestrial ecosystems, and the estimated age of the oldest terrestrial lichen fossil is 400 Ma; [123] this date corresponds to the age of the oldest known sporocarp fossil, a Paleopyrenomycites species found in the Rhynie Chert. [124] The oldest fossil with microscopic features resembling modern-day basidiomycetes is Palaeoancistrus, found permineralized with a fern from the Pennsylvanian. [125] Rare in the fossil record are the Homobasidiomycetes (a taxon roughly equivalent to the mushroom-producing species of the Agaricomycetes). Two amber-preserved specimens provide evidence that the earliest known mushroom-forming fungi (the extinct species Archaeomarasmius leggetti ) appeared during the late Cretaceous, 90 Ma. [126] [127]

Some time after the Permian–Triassic extinction event (251.4 Ma), a fungal spike (originally thought to be an extraordinary abundance of fungal spores in sediments) formed, suggesting that fungi were the dominant life form at this time, representing nearly 100% of the available fossil record for this period. [128] However, the relative proportion of fungal spores relative to spores formed by algal species is difficult to assess, [129] the spike did not appear worldwide, [130] [131] and in many places it did not fall on the Permian–Triassic boundary. [132]

65 million years ago, immediately after the Cretaceous–Paleogene extinction event that famously killed off most dinosaurs, there is a dramatic increase in evidence of fungi, apparently the death of most plant and animal species leading to a huge fungal bloom like "a massive compost heap". [133]

Taxonomy

Although commonly included in botany curricula and textbooks, fungi are more closely related to animals than to plants and are placed with the animals in the monophyletic group of opisthokonts. [134] Analyses using molecular phylogenetics support a monophyletic origin of fungi. [44] The taxonomy of fungi is in a state of constant flux, especially due to recent research based on DNA comparisons. These current phylogenetic analyses often overturn classifications based on older and sometimes less discriminative methods based on morphological features and biological species concepts obtained from experimental matings. [135]

There is no unique generally accepted system at the higher taxonomic levels and there are frequent name changes at every level, from species upwards. Efforts among researchers are now underway to establish and encourage usage of a unified and more consistent nomenclature. [44] [136] Fungal species can also have multiple scientific names depending on their life cycle and mode (sexual or asexual) of reproduction. Web sites such as Index Fungorum and ITIS list current names of fungal species (with cross-references to older synonyms).

The 2007 classification of Kingdom Fungi is the result of a large-scale collaborative research effort involving dozens of mycologists and other scientists working on fungal taxonomy. [44] It recognizes seven phyla, two of which—the Ascomycota and the Basidiomycota—are contained within a branch representing subkingdom Dikarya, the most species rich and familiar group, including all the mushrooms, most food-spoilage molds, most plant pathogenic fungi, and the beer, wine, and bread yeasts. The accompanying cladogram depicts the major fungal taxa and their relationship to opisthokont and unikont organisms, based on the work of Philippe Silar, [137] "The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research" [138] and Tedersoo et al. 2018. [139] The lengths of the branches are not proportional to evolutionary distances.

Zoosporia
Rozellomyceta
Rozellomycota

Rozellomycetes

Microsporidiomycota

Mitosporidium

Paramicrosporidium

Nucleophaga

Metchnikovellea

Microsporea

Aphelidiomyceta
Aphelidiomycota

Aphelidiomycetes

Eumycota
Chytridiomyceta
Neocallimastigomycota

Neocallimastigomycetes

Chytridiomycota
Monoblepharomycotina

Hyaloraphidiomycetes

Monoblepharidomycetes

Sanchytriomycetes

Chytridiomycotina

Mesochytriomycetes

Chytridiomycetes

Blastocladiomyceta
Blastocladiomycota

Blastocladiomycetes

Physodermatomycetes

Amastigomycota
Zoopagomyceta
Basidiobolomycota

Basidiobolomycetes

Olpidiomycetes

Entomophthoromycota

Neozygitomycetes

Entomophthoromycetes

Kickxellomycota
Zoopagomycotina

Zoopagomycetes

Kickxellomycotina

Dimargaritomycetes

Kickxellomycetes

Mortierellomycota

Mortierellomycetes

Mucoromyceta
Calcarisporiellomycota

Calcarisporiellomycetes

Mucoromycota

Umbelopsidomycetes

Mucoromycetes

Symbiomycota
Glomeromycota

Paraglomeromycetes

Archaeosporomycetes

Glomeromycetes

Dikarya
Entorrhizomycota

Entorrhizomycetes

Basidiomycota

Ascomycota

Basidiomycota
Pucciniomycotina

Tritirachiomycetes

Mixiomycetes

Agaricostilbomycetes

Cystobasidiomycetes

Classiculaceae

Microbotryomycetes

Cryptomycocolacomycetes

Atractiellomycetes

Pucciniomycetes

Orthomycotina
Ustilaginomycotina

Monilielliomycetes

Malasseziomycetes

Ustilaginomycetes

Exobasidiomycetes

Agaricomycotina

?Geminibasidiomycetes

?Wallemiomycetes

Bartheletiomycetes

Tremellomycetes

Dacrymycetes

Agaricomycetes

Ascomycota
Taphrinomycotina

Neolectomycetes

Taphrinomycetes

Schizosaccharomyceta

Archaeorhizomycetes

Pneumocystidomycetes

Schizosaccharomycetes

Saccharomyceta
Saccharomycotina

Saccharomycetes

Pezizomycotina

?Thelocarpales

?Vezdaeales

?Lahmiales

?Triblidiales

Orbiliomycetes

Pezizomycetes

Leotiomyceta
Sordariomyceta

Xylonomycetes

Geoglossomycetes

Leotiomycetes

Laboulbeniomycetes

Sordariomycetes

Dothideomyceta

Coniocybomycetes

Lichinomycetes

Eurotiomycetes

Lecanoromycetes

Collemopsidiomycetes

Arthoniomycetes

Dothideomycetes

Taxonomic groups

Main groups of fungi. 02 01 groups of Fungi (M. Piepenbring).png
Main groups of fungi.

The major phyla (sometimes called divisions) of fungi have been classified mainly on the basis of characteristics of their sexual reproductive structures. Currently, seven phyla are proposed: Microsporidia, Chytridiomycota, Blastocladiomycota, Neocallimastigomycota, Glomeromycota, Ascomycota, and Basidiomycota. [44]

Phylogenetic analysis has demonstrated that the Microsporidia, unicellular parasites of animals and protists, are fairly recent and highly derived endobiotic fungi (living within the tissue of another species). [110] [140] One 2006 study concludes that the Microsporidia are a sister group to the true fungi; that is, they are each other's closest evolutionary relative. [141] Hibbett and colleagues suggest that this analysis does not clash with their classification of the Fungi, and although the Microsporidia are elevated to phylum status, it is acknowledged that further analysis is required to clarify evolutionary relationships within this group. [44]

The Chytridiomycota are commonly known as chytrids. These fungi are distributed worldwide. Chytrids and their close relatives Neocallimastigomycota and Blastocladiomycota (below) are the only fungi with active motility, producing zoospores that are capable of active movement through aqueous phases with a single flagellum, leading early taxonomists to classify them as protists. Molecular phylogenies, inferred from rRNA sequences in ribosomes, suggest that the Chytrids are a basal group divergent from the other fungal phyla, consisting of four major clades with suggestive evidence for paraphyly or possibly polyphyly. [142]

The Blastocladiomycota were previously considered a taxonomic clade within the Chytridiomycota. Recent molecular data and ultrastructural characteristics, however, place the Blastocladiomycota as a sister clade to the Zygomycota, Glomeromycota, and Dikarya (Ascomycota and Basidiomycota). The blastocladiomycetes are saprotrophs, feeding on decomposing organic matter, and they are parasites of all eukaryotic groups. Unlike their close relatives, the chytrids, most of which exhibit zygotic meiosis, the blastocladiomycetes undergo sporic meiosis. [110]

The Neocallimastigomycota were earlier placed in the phylum Chytridomycota. Members of this small phylum are anaerobic organisms, living in the digestive system of larger herbivorous mammals and in other terrestrial and aquatic environments enriched in cellulose (e.g., domestic waste landfill sites). [143] They lack mitochondria but contain hydrogenosomes of mitochondrial origin. As in the related chrytrids, neocallimastigomycetes form zoospores that are posteriorly uniflagellate or polyflagellate. [44]

Arbuscular mycorrhiza seen under microscope. Flax root cortical cells containing paired arbuscules. Arbuscular mycorrhiza microscope.jpg
Arbuscular mycorrhiza seen under microscope. Flax root cortical cells containing paired arbuscules.
Diagram of an apothecium (the typical cup-like reproductive structure of Ascomycetes) showing sterile tissues as well as developing and mature asci. Ascocarp2.png
Diagram of an apothecium (the typical cup-like reproductive structure of Ascomycetes) showing sterile tissues as well as developing and mature asci.

Members of the Glomeromycota form arbuscular mycorrhizae, a form of mutualist symbiosis wherein fungal hyphae invade plant root cells and both species benefit from the resulting increased supply of nutrients. All known Glomeromycota species reproduce asexually. [81] The symbiotic association between the Glomeromycota and plants is ancient, with evidence dating to 400 million years ago. [144] Formerly part of the Zygomycota (commonly known as 'sugar' and 'pin' molds), the Glomeromycota were elevated to phylum status in 2001 and now replace the older phylum Zygomycota. [145] Fungi that were placed in the Zygomycota are now being reassigned to the Glomeromycota, or the subphyla incertae sedis Mucoromycotina, Kickxellomycotina, the Zoopagomycotina and the Entomophthoromycotina. [44] Some well-known examples of fungi formerly in the Zygomycota include black bread mold ( Rhizopus stolonifer ), and Pilobolus species, capable of ejecting spores several meters through the air. [146] Medically relevant genera include Mucor , Rhizomucor , and Rhizopus .

The Ascomycota, commonly known as sac fungi or ascomycetes, constitute the largest taxonomic group within the Eumycota. [43] These fungi form meiotic spores called ascospores, which are enclosed in a special sac-like structure called an ascus. This phylum includes morels, a few mushrooms and truffles, unicellular yeasts (e.g., of the genera Saccharomyces , Kluyveromyces , Pichia , and Candida ), and many filamentous fungi living as saprotrophs, parasites, and mutualistic symbionts (e.g. lichens). Prominent and important genera of filamentous ascomycetes include Aspergillus , Penicillium , Fusarium , and Claviceps . Many ascomycete species have only been observed undergoing asexual reproduction (called anamorphic species), but analysis of molecular data has often been able to identify their closest teleomorphs in the Ascomycota. [147] Because the products of meiosis are retained within the sac-like ascus, ascomycetes have been used for elucidating principles of genetics and heredity (e.g., Neurospora crassa ). [148]

Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia. Most common mushrooms belong to this group, as well as rust and smut fungi, which are major pathogens of grains. Other important basidiomycetes include the maize pathogen Ustilago maydis , [149] human commensal species of the genus Malassezia , [150] and the opportunistic human pathogen, Cryptococcus neoformans . [151]

Fungus-like organisms

Because of similarities in morphology and lifestyle, the slime molds (mycetozoans, plasmodiophorids, acrasids, Fonticula and labyrinthulids, now in Amoebozoa, Rhizaria, Excavata, Opisthokonta and Stramenopiles, respectively), water molds (oomycetes) and hyphochytrids (both Stramenopiles) were formerly classified in the kingdom Fungi, in groups like Mastigomycotina, Gymnomycota and Phycomycetes. The slime molds were studied also as protozoans, leading to an ambiregnal, duplicated taxonomy.

Unlike true fungi, the cell walls of oomycetes contain cellulose and lack chitin. Hyphochytrids have both chitin and cellulose. Slime molds lack a cell wall during the assimilative phase (except labyrinthulids, which have a wall of scales), and ingest nutrients by ingestion (phagocytosis, except labyrinthulids) rather than absorption (osmotrophy, as fungi, labyrinthulids, oomycetes and hyphochytrids). Neither water molds nor slime molds are closely related to the true fungi, and, therefore, taxonomists no longer group them in the kingdom Fungi. Nonetheless, studies of the oomycetes and myxomycetes are still often included in mycology textbooks and primary research literature. [152]

The Eccrinales and Amoebidiales are opisthokont protists, previously thought to be zygomycete fungi. Other groups now in Opisthokonta (e.g., Corallochytrium , Ichthyosporea) were also at given time classified as fungi. The genus Blastocystis , now in Stramenopiles, was originally classified as a yeast. Ellobiopsis , now in Alveolata, was considered a chytrid. The bacteria were also included in fungi in some classifications, as the group Schizomycetes.

The Rozellida clade, including the "ex-chytrid" Rozella , is a genetically disparate group known mostly from environmental DNA sequences that is a sister group to fungi. Members of the group that have been isolated lack the chitinous cell wall that is characteristic of fungi.

The nucleariids may be the next sister group to the eumycete clade, and as such could be included in an expanded fungal kingdom. [134]

Ecology

A pin mold decomposing a peach PinMould on Peach LowMag Scale.jpg
A pin mold decomposing a peach

Although often inconspicuous, fungi occur in every environment on Earth and play very important roles in most ecosystems. Along with bacteria, fungi are the major decomposers in most terrestrial (and some aquatic) ecosystems, and therefore play a critical role in biogeochemical cycles [153] and in many food webs. As decomposers, they play an essential role in nutrient cycling, especially as saprotrophs and symbionts, degrading organic matter to inorganic molecules, which can then re-enter anabolic metabolic pathways in plants or other organisms. [154] [155]

Symbiosis

Many fungi have important symbiotic relationships with organisms from most if not all Kingdoms. [156] [157] [158] These interactions can be mutualistic or antagonistic in nature, or in the case of commensal fungi are of no apparent benefit or detriment to the host. [159] [160] [161]

With plants

Mycorrhizal symbiosis between plants and fungi is one of the most well-known plant–fungus associations and is of significant importance for plant growth and persistence in many ecosystems; over 90% of all plant species engage in mycorrhizal relationships with fungi and are dependent upon this relationship for survival. [162]

The dark filaments are hyphae of the endophytic fungus Neotyphodium coenophialum in the intercellular spaces of tall fescue leaf sheath tissue Neotyphodium coenophialum.jpg
The dark filaments are hyphae of the endophytic fungus Neotyphodium coenophialum in the intercellular spaces of tall fescue leaf sheath tissue

The mycorrhizal symbiosis is ancient, dating to at least 400 million years ago. [144] It often increases the plant's uptake of inorganic compounds, such as nitrate and phosphate from soils having low concentrations of these key plant nutrients. [154] [163] The fungal partners may also mediate plant-to-plant transfer of carbohydrates and other nutrients. [164] Such mycorrhizal communities are called "common mycorrhizal networks". [165] [166] A special case of mycorrhiza is myco-heterotrophy, whereby the plant parasitizes the fungus, obtaining all of its nutrients from its fungal symbiont. [167] Some fungal species inhabit the tissues inside roots, stems, and leaves, in which case they are called endophytes. [168] Similar to mycorrhiza, endophytic colonization by fungi may benefit both symbionts; for example, endophytes of grasses impart to their host increased resistance to herbivores and other environmental stresses and receive food and shelter from the plant in return. [169]

With algae and cyanobacteria

The lichen Lobaria pulmonaria, a symbiosis of fungal, algal, and cyanobacterial species Lobaria pulmonaria 010108a.jpg
The lichen Lobaria pulmonaria , a symbiosis of fungal, algal, and cyanobacterial species

Lichens are a symbiotic relationship between fungi and photosynthetic algae or cyanobacteria. The photosynthetic partner in the relationship is referred to in lichen terminology as a "photobiont". The fungal part of the relationship is composed mostly of various species of ascomycetes and a few basidiomycetes. [170] Lichens occur in every ecosystem on all continents, play a key role in soil formation and the initiation of biological succession, [171] and are prominent in some extreme environments, including polar, alpine, and semiarid desert regions. [172] They are able to grow on inhospitable surfaces, including bare soil, rocks, tree bark, wood, shells, barnacles and leaves. [173] As in mycorrhizas, the photobiont provides sugars and other carbohydrates via photosynthesis to the fungus, while the fungus provides minerals and water to the photobiont. The functions of both symbiotic organisms are so closely intertwined that they function almost as a single organism; in most cases the resulting organism differs greatly from the individual components. Lichenization is a common mode of nutrition for fungi; around 20% of fungi—between 17,500 and 20,000 described species—are lichenized. [174] Characteristics common to most lichens include obtaining organic carbon by photosynthesis, slow growth, small size, long life, long-lasting (seasonal) vegetative reproductive structures, mineral nutrition obtained largely from airborne sources, and greater tolerance of desiccation than most other photosynthetic organisms in the same habitat. [175]

With insects

Many insects also engage in mutualistic relationships with fungi. Several groups of ants cultivate fungi in the order Agaricales as their primary food source, while ambrosia beetles cultivate various species of fungi in the bark of trees that they infest. [176] Likewise, females of several wood wasp species (genus Sirex ) inject their eggs together with spores of the wood-rotting fungus Amylostereum areolatum into the sapwood of pine trees; the growth of the fungus provides ideal nutritional conditions for the development of the wasp larvae. [177] At least one species of stingless bee has a relationship with a fungus in the genus Monascus , where the larvae consume and depend on fungus transferred from old to new nests. [178] Termites on the African savannah are also known to cultivate fungi, [156] and yeasts of the genera Candida and Lachancea inhabit the gut of a wide range of insects, including neuropterans, beetles, and cockroaches; it is not known whether these fungi benefit their hosts. [179] The larvae of many families of fungicolous flies, particularly those within the superfamily Sciaroidea such as the Mycetophilidae and some Keroplatidae feed on fungal fruiting bodies and sterile mycorrhizae. [180]

As pathogens and parasites

The plant pathogen Aecidium magellanicum causes calafate rust, seen here on a Berberis shrub in Chile. Aecidium magnellanicum.jpg
The plant pathogen Aecidium magellanicum causes calafate rust, seen here on a Berberis shrub in Chile.

Many fungi are parasites on plants, animals (including humans), and other fungi. Serious pathogens of many cultivated plants causing extensive damage and losses to agriculture and forestry include the rice blast fungus Magnaporthe oryzae , [181] tree pathogens such as Ophiostoma ulmi and Ophiostoma novo-ulmi causing Dutch elm disease [182] and Cryphonectria parasitica responsible for chestnut blight, [183] and plant pathogens in the genera Fusarium , Ustilago , Alternaria , and Cochliobolus . [160] Some carnivorous fungi, like Paecilomyces lilacinus , are predators of nematodes, which they capture using an array of specialized structures such as constricting rings or adhesive nets. [184] Many fungi that are plant pathogens, such as Magnaporthe oryzae, can switch from being biotrophic (parasitic on living plants) to being necrotrophic (feeding on the dead tissues of plants they have killed). [185] This same principle is applied to fungi-feeding parasites, including Asterotremella albida , which feeds on the fruit bodies of other fungi both while they are living and after they are dead. [186]

Some fungi can cause serious diseases in humans, several of which may be fatal if untreated. These include aspergillosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mycetomas, and paracoccidioidomycosis. Furthermore, persons with immuno-deficiencies are particularly susceptible to disease by genera such as Aspergillus , Candida , Cryptoccocus , [161] [187] [188] Histoplasma , [189] and Pneumocystis . [190] Other fungi can attack eyes, nails, hair, and especially skin, the so-called dermatophytic and keratinophilic fungi, and cause local infections such as ringworm and athlete's foot. [191] Fungal spores are also a cause of allergies, and fungi from different taxonomic groups can evoke allergic reactions. [192]

As targets of mycoparasites

The organisms which parasitize fungi are known as mycoparasitic organisms. Certain species of the genus Pythium , which are oomycetes, have potential as biocontrol agents against certain fungi. [193] Fungi can also act as mycoparasites or antagonists of other fungi, such as Hypomyces chrysospermus , which grows on bolete mushrooms.

Mycotoxins

Ergotamine, a major mycotoxin produced by Claviceps species, which if ingested can cause gangrene, convulsions, and hallucinations Ergotamine3.png
Ergotamine, a major mycotoxin produced by Claviceps species, which if ingested can cause gangrene, convulsions, and hallucinations

Many fungi produce biologically active compounds, several of which are toxic to animals or plants and are therefore called mycotoxins. Of particular relevance to humans are mycotoxins produced by molds causing food spoilage, and poisonous mushrooms (see above). Particularly infamous are the lethal amatoxins in some Amanita mushrooms, and ergot alkaloids, which have a long history of causing serious epidemics of ergotism (St Anthony's Fire) in people consuming rye or related cereals contaminated with sclerotia of the ergot fungus, Claviceps purpurea . [194] Other notable mycotoxins include the aflatoxins, which are insidious liver toxins and highly carcinogenic metabolites produced by certain Aspergillus species often growing in or on grains and nuts consumed by humans, ochratoxins, patulin, and trichothecenes (e.g., T-2 mycotoxin) and fumonisins, which have significant impact on human food supplies or animal livestock. [195]

Mycotoxins are secondary metabolites (or natural products), and research has established the existence of biochemical pathways solely for the purpose of producing mycotoxins and other natural products in fungi. [33] Mycotoxins may provide fitness benefits in terms of physiological adaptation, competition with other microbes and fungi, and protection from consumption (fungivory). [196] [197] Many fungal secondary metabolites (or derivatives) are used medically, as described under Human Use below.

Pathogenic mechanisms

Ustilago maydis is a pathogenic plant fungus that causes smut disease in maize and teosinte. Plants have evolved efficient defense systems against pathogenic microbes such as U. maydis. A rapid defense reaction after pathogen attack is the oxidative burst where the plant produces reactive oxygen species at the site of the attempted invasion. U. maydis can respond to the oxidative burst with an oxidative stress response, regulated by the gene YAP1 . The response protects U. maydis from the host defense, and is necessary for the pathogen's virulence. [198] Furthermore, U. maydis has a well-established recombinational DNA repair system which acts during mitosis and meiosis. [199] The system may assist the pathogen in surviving DNA damage arising from the host plant's oxidative defensive response to infection. [200]

Cryptococcus neoformans is an encapsulated yeast that can live in both plants and animals. C. neoformans usually infects the lungs, where it is phagocytosed by alveolar macrophages. [201] Some C. neoformans can survive inside macrophages, which appears to be the basis for latency, disseminated disease, and resistance to antifungal agents. One mechanism by which C. neoformans survives the hostile macrophage environment is by up-regulating the expression of genes involved in the oxidative stress response. [201] Another mechanism involves meiosis. The majority of C. neoformans are mating "type a". Filaments of mating "type a" ordinarily have haploid nuclei, but they can become diploid (perhaps by endoduplication or by stimulated nuclear fusion) to form blastospores. The diploid nuclei of blastospores can undergo meiosis, including recombination, to form haploid basidiospores that can be dispersed. [202] This process is referred to as monokaryotic fruiting. This process requires a gene called DMC1 , which is a conserved homologue of genes recA in bacteria and RAD51 in eukaryotes, that mediates homologous chromosome pairing during meiosis and repair of DNA double-strand breaks. Thus, C. neoformans can undergo a meiosis, monokaryotic fruiting, that promotes recombinational repair in the oxidative, DNA damaging environment of the host macrophage, and the repair capability may contribute to its virulence. [200] [202]

Human use

Saccharomyces cerevisiae cells shown with DIC microscopy S cerevisiae under DIC microscopy.jpg
Saccharomyces cerevisiae cells shown with DIC microscopy

The human use of fungi for food preparation or preservation and other purposes is extensive and has a long history. Mushroom farming and mushroom gathering are large industries in many countries. The study of the historical uses and sociological impact of fungi is known as ethnomycology. Because of the capacity of this group to produce an enormous range of natural products with antimicrobial or other biological activities, many species have long been used or are being developed for industrial production of antibiotics, vitamins, and anti-cancer and cholesterol-lowering drugs. More recently, methods have been developed for genetic engineering of fungi, [203] enabling metabolic engineering of fungal species. For example, genetic modification of yeast species [204] —which are easy to grow at fast rates in large fermentation vessels—has opened up ways of pharmaceutical production that are potentially more efficient than production by the original source organisms. [205]

Therapeutic uses

Modern chemotherapeutics

The mould Penicillium chrysogenum was the source of penicillin G. Penicillium notatum.jpg
The mould Penicillium chrysogenum was the source of penicillin G.

Many species produce metabolites that are major sources of pharmacologically active drugs. Particularly important are the antibiotics, including the penicillins, a structurally related group of β-lactam antibiotics that are synthesized from small peptides. Although naturally occurring penicillins such as penicillin G (produced by Penicillium chrysogenum ) have a relatively narrow spectrum of biological activity, a wide range of other penicillins can be produced by chemical modification of the natural penicillins. Modern penicillins are semisynthetic compounds, obtained initially from fermentation cultures, but then structurally altered for specific desirable properties. [206] Other antibiotics produced by fungi include: ciclosporin, commonly used as an immunosuppressant during transplant surgery; and fusidic acid, used to help control infection from methicillin-resistant Staphylococcus aureus bacteria. [207] Widespread use of antibiotics for the treatment of bacterial diseases, such as tuberculosis, syphilis, leprosy, and others began in the early 20th century and continues to date. In nature, antibiotics of fungal or bacterial origin appear to play a dual role: at high concentrations they act as chemical defense against competition with other microorganisms in species-rich environments, such as the rhizosphere, and at low concentrations as quorum-sensing molecules for intra- or interspecies signaling. [208] Other drugs produced by fungi include griseofulvin isolated from Penicillium griseofulvum , used to treat fungal infections, [209] and statins (HMG-CoA reductase inhibitors), used to inhibit cholesterol synthesis. Examples of statins found in fungi include mevastatin from Penicillium citrinum and lovastatin from Aspergillus terreus and the oyster mushroom. [210] Fungi produce compounds that inhibit viruses [211] [212] and cancer cells. [213] [214] Specific metabolites, such as polysaccharide-K, ergotamine, and β-lactam antibiotics, are routinely used in clinical medicine. The shiitake mushroom is a source of lentinan, a clinical drug approved for use in cancer treatments in several countries, including Japan. [215] [216] In Europe and Japan, polysaccharide-K (brand name Krestin), a chemical derived from Trametes versicolor , is an approved adjuvant for cancer therapy. [217]

Traditional and folk medicine

Ganoderma lucidum 01.jpg
CordycepsSinensis.jpg
The medicinal fungi Ganoderma lucidum (left) and Ophiocordyceps sinensis (right)

Certain mushrooms enjoy usage as therapeutics in folk medicines, such as Traditional Chinese medicine. Notable medicinal mushrooms with a well-documented history of use include Agaricus subrufescens , [213] [218] Ganoderma lucidum , [219] Psilocybe and Ophiocordyceps sinensis . [220]

Cultured foods

Baker's yeast or Saccharomyces cerevisiae , a unicellular fungus, is used to make bread and other wheat-based products, such as pizza dough and dumplings. [221] Yeast species of the genus Saccharomyces are also used to produce alcoholic beverages through fermentation. [222] Shoyu koji mold ( Aspergillus oryzae ) is an essential ingredient in brewing Shoyu (soy sauce) and sake, and the preparation of miso, [223] while Rhizopus species are used for making tempeh. [224] Several of these fungi are domesticated species that were bred or selected according to their capacity to ferment food without producing harmful mycotoxins (see below), which are produced by very closely related Aspergilli . [225] Quorn, a meat substitute, is made from Fusarium venenatum . [226]

In food

A selection of edible mushrooms eaten in Asia Asian mushrooms.jpg
A selection of edible mushrooms eaten in Asia

Edible mushrooms include commercially raised and wild-harvested fungi. Agaricus bisporus , sold as button mushrooms when small or Portobello mushrooms when larger, is the most widely cultivated species in the West, used in salads, soups, and many other dishes. Many Asian fungi are commercially grown and have increased in popularity in the West. They are often available fresh in grocery stores and markets, including straw mushrooms ( Volvariella volvacea ), oyster mushrooms ( Pleurotus ostreatus ), shiitakes ( Lentinula edodes ), and enokitake ( Flammulina spp.). [227]

Stilton cheese veined with Penicillium roqueforti Blue Stilton Quarter Front.jpg
Stilton cheese veined with Penicillium roqueforti

Many other mushroom species are harvested from the wild for personal consumption or commercial sale. Milk mushrooms, morels, chanterelles, truffles, black trumpets, and porcini mushrooms ( Boletus edulis ) (also known as king boletes) demand a high price on the market. They are often used in gourmet dishes. [228]

Certain types of cheeses require inoculation of milk curds with fungal species that impart a unique flavor and texture to the cheese. Examples include the blue color in cheeses such as Stilton or Roquefort, which are made by inoculation with Penicillium roqueforti . [229] Molds used in cheese production are non-toxic and are thus safe for human consumption; however, mycotoxins (e.g., aflatoxins, roquefortine C, patulin, or others) may accumulate because of growth of other fungi during cheese ripening or storage. [230]

Poisonous fungi

Amanita phalloides accounts for the majority of fatal mushroom poisonings worldwide. It sometimes lacks the greenish color seen here. Amanita phalloides 1.JPG
Amanita phalloides accounts for the majority of fatal mushroom poisonings worldwide. It sometimes lacks the greenish color seen here.

Many mushroom species are poisonous to humans and cause a range of reactions including slight digestive problems, allergic reactions, hallucinations, severe organ failure, and death. Genera with mushrooms containing deadly toxins include Conocybe , Galerina , Lepiota , and, the most infamous, Amanita . [231] The latter genus includes the destroying angel (A. virosa) and the death cap (A. phalloides), the most common cause of deadly mushroom poisoning. [232] The false morel ( Gyromitra esculenta ) is occasionally considered a delicacy when cooked, yet can be highly toxic when eaten raw. [233] Tricholoma equestre was considered edible until it was implicated in serious poisonings causing rhabdomyolysis. [234] Fly agaric mushrooms (Amanita muscaria) also cause occasional non-fatal poisonings, mostly as a result of ingestion for its hallucinogenic properties. Historically, fly agaric was used by different peoples in Europe and Asia and its present usage for religious or shamanic purposes is reported from some ethnic groups such as the Koryak people of north-eastern Siberia. [235]

As it is difficult to accurately identify a safe mushroom without proper training and knowledge, it is often advised to assume that a wild mushroom is poisonous and not to consume it. [236] [237]

Pest control

Grasshoppers killed by Beauveria bassiana Beauveria.jpg
Grasshoppers killed by Beauveria bassiana

In agriculture, fungi may be useful if they actively compete for nutrients and space with pathogenic microorganisms such as bacteria or other fungi via the competitive exclusion principle, [238] or if they are parasites of these pathogens. For example, certain species may be used to eliminate or suppress the growth of harmful plant pathogens, such as insects, mites, weeds, nematodes, and other fungi that cause diseases of important crop plants. [239] This has generated strong interest in practical applications that use these fungi in the biological control of these agricultural pests. Entomopathogenic fungi can be used as biopesticides, as they actively kill insects. [240] Examples that have been used as biological insecticides are Beauveria bassiana , Metarhizium spp, Hirsutella spp, Paecilomyces (Isaria) spp, and Lecanicillium lecanii . [241] [242] Endophytic fungi of grasses of the genus Neotyphodium , such as N. coenophialum , produce alkaloids that are toxic to a range of invertebrate and vertebrate herbivores. These alkaloids protect grass plants from herbivory, but several endophyte alkaloids can poison grazing animals, such as cattle and sheep. [243] Infecting cultivars of pasture or forage grasses with Neotyphodium endophytes is one approach being used in grass breeding programs; the fungal strains are selected for producing only alkaloids that increase resistance to herbivores such as insects, while being non-toxic to livestock. [244]

Bioremediation

Certain fungi, in particular white-rot fungi, can degrade insecticides, herbicides, pentachlorophenol, creosote, coal tars, and heavy fuels and turn them into carbon dioxide, water, and basic elements. [245] Fungi have been shown to biomineralize uranium oxides, suggesting they may have application in the bioremediation of radioactively polluted sites. [246] [247] [248]

Model organisms

Several pivotal discoveries in biology were made by researchers using fungi as model organisms, that is, fungi that grow and sexually reproduce rapidly in the laboratory. For example, the one gene-one enzyme hypothesis was formulated by scientists using the bread mold Neurospora crassa to test their biochemical theories. [249] Other important model fungi are Aspergillus nidulans and the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe , each of which with a long history of use to investigate issues in eukaryotic cell biology and genetics, such as cell cycle regulation, chromatin structure, and gene regulation. Other fungal models have more recently emerged that address specific biological questions relevant to medicine, plant pathology, and industrial uses; examples include Candida albicans , a dimorphic, opportunistic human pathogen, [250] Magnaporthe grisea , a plant pathogen, [251] and Pichia pastoris , a yeast widely used for eukaryotic protein production. [252]

Others

Fungi are used extensively to produce industrial chemicals like citric, gluconic, lactic, and malic acids, [253] and industrial enzymes, such as lipases used in biological detergents, [254] cellulases used in making cellulosic ethanol [255] and stonewashed jeans, [256] and amylases, [257] invertases, proteases and xylanases. [258]

See also

Related Research Articles

Ascomycota division of fungi

Ascomycota division or phylum of the kingdom Fungi that, together with the Basidiomycota, form the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defining feature of this fungal group is the "ascus", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle and thus do not form asci or ascospores. Familiar examples of sac fungi include morels, truffles, brewer's yeast and baker's yeast, dead man's fingers, and cup fungi. The fungal symbionts in the majority of lichens such as Cladonia belong to the Ascomycota. Ascomycota is a monophyletic group. Previously placed in the Deuteromycota along with asexual species from other fungal taxa, asexual ascomycetes are now identified and classified based on morphological or physiological similarities to ascus-bearing taxa, and by phylogenetic analyses of DNA sequences. The ascomycetes are of particular use to humans as sources of medicinally important compounds, such as antibiotics, for fermenting bread, alcoholic beverages and cheese. Penicillium species on cheeses and those producing antibiotics for treating bacterial infectious diseases are examples of ascomycetes. Many ascomycetes are pathogens, both of animals, including humans, and of plants. Examples of ascomycetes that can cause infections in humans include Candida albicans, Aspergillus niger and several tens of species that cause skin infections. The many plant-pathogenic ascomycetes include apple scab, rice blast, the ergot fungi, black knot, and the powdery mildews. Several species of ascomycetes are biological model organisms in laboratory research. Most famously, Neurospora crassa, several species of yeasts, and Aspergillus species are used in many genetics and cell biology studies.

Hypha long, filamentous structure in fungi or Actinobacteria

A hypha is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.

Oomycete fungus-like organism

Oomycota or oomycetes form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms. They are filamentous, microscopic, absorptive organisms that reproduce both sexually and asexually. Sexual reproduction of an oospore is the result of contact between hyphae of a male antheridia and female oogonia; this spore can overwinter and is known as a resting spore. Asexual reproduction is the formation of chlamydospore and sporangia producing zoospores. Oomycetes occupy both saprophytic and pathogenic lifestyles, and include some of the most notorious pathogens of plants, causing devastating diseases such as late blight of potato and sudden oak death. One oomycete, the mycoparasite Pythium oligandrum, is used for biocontrol, attacking plant pathogenic fungi. The oomycetes are also often referred to as water molds, although the water-preferring nature which led to that name is not true of most species, which are terrestrial pathogens. The Oomycota have a very sparse fossil record. A possible oomycete has been described from Cretaceous amber.

Agaricales order of fungi

The fungal order Agaricales, also known as gilled mushrooms or euagarics, contains some of the most familiar types of mushrooms. The order has 33 extant families, 413 genera, and over 13000 described species, along with six extinct genera known only from the fossil record. They range from the ubiquitous common mushroom to the deadly destroying angel and the hallucinogenic fly agaric to the bioluminescent jack-o-lantern mushroom.

<i>Aspergillus flavus</i> aspergillus flavus

Aspergillus flavus is a saprotrophic and pathogenic fungus with a cosmopolitan distribution. It is best known for its colonization of cereal grains, legumes, and tree nuts. Postharvest rot typically develops during harvest, storage, and/or transit. A. flavus infections can occur while hosts are still in the field (preharvest), but often show no symptoms (dormancy) until postharvest storage and/or transport. In addition to causing preharvest and postharvest infections, many strains produce significant quantities of toxic compounds known as mycotoxins, which, when consumed, are toxic to mammals. A. flavus is also an opportunistic human and animal pathogen, causing aspergillosis in immunocompromised individuals.

Endophyte

An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; however, most of the endophyte/plant relationships are not well understood. Some endophytes may enhance host growth, nutrient acquisition and improve the plant's ability to tolerate abiotic stresses, such as drought, and decrease biotic stresses by enhancing plant resistance to insects, pathogens and herbivores.

Conidium

A conidium, sometimes termed an asexual chlamydospore or chlamydoconidium, is an asexual, non-motile spore of a fungus. The name comes from the Greek word for dust, κόνις kónis. They are also called mitospores due to the way they are generated through the cellular process of mitosis. The two new haploid cells are genetically identical to the haploid parent, and can develop into new organisms if conditions are favorable, and serve in biological dispersal.

Mating in fungi

Mating in fungi is a complex process governed by mating types. Research on fungal mating has focused on several model species with different behaviour. Not all fungi reproduce sexually and many that do are isogamous; thus, the terms "male" and "female" do not apply to many members of the fungal kingdom. Homothallic species are able to mate with themselves, while in heterothallic species only isolates of opposite mating types can mate.

<i>Eremothecium gossypii</i> filamentous fungus or mold closely related to yeast

Eremothecium gossypii (also known as Ashbya gossypii) is a filamentous fungus or mold closely related to yeast, but growing exclusively in a filamentous way. It was originally isolated from cotton as a pathogen causing stigmatomycosis by Ashby and Nowell in 1926. This disease affects the development of hair cells in cotton bolls and can be transmitted to citrus fruits, which thereupon dry out and collapse (dry rot disease). In the first part of the 20th century, E. gossypii and two other fungi causing stigmatomycosis (Eremothecium coryli, Aureobasidium pullulans) made it virtually impossible to grow cotton in certain regions of the subtropics, causing severe economical losses. Control of the spore-transmitting insects - cotton stainer (Dysdercus suturellus) and Antestiopsis (antestia bugs) - permitted full eradication of infections. E. gossypii was recognized as a natural overproducer of riboflavin (vitamin B2), which protects its spores against ultraviolet light. This made it an interesting organism for industries, where genetically modified strains are still used to produce this vitamin.

Filobasidiella is a genus of fungi in the family Tremellaceae. Species are parasitic on other fungi and do not produce distinct basidiocarps. The genus is the teleomorphic (sexual) state of the yeast genus Cryptococcus, some species of which are human pathogens.

Mycelial cord

Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functions; hence they are also called rhizomorphs.

<i>Aureobasidium pullulans</i> species of fungus

Aureobasidium pullulans is a ubiquitous black, yeast-like fungus that can be found in different environments. It is well known as a naturally occurring epiphyte or endophyte of a wide range of plant species without causing any symptoms of disease. A. pullulans has a high importance in biotechnology for the production of different enzymes, siderophores and pullulan. Furthermore, A. pullulans is used in biological control of plant diseases, especially storage diseases.

<i>Phaeosphaeria nodorum</i> species of fungus

Phaeosphaeria nodorum is a major fungal pathogen of wheat and a member of the Dothideomycetes, a large fungal taxon that includes many important plant pathogens affecting all major crop plant families.

<i>Geotrichum candidum</i> Geotricum candidum

Geotrichum candidum is a fungus which is a member of the human microbiome, notably associated with skin, sputum and feces where it occurs in 25-30% of specimens. It is common in soil and has been isolated from soil collected around the world, in all continents.

Pucciniomycotina subdivision of fungi

Pucciniomycotina is a subdivision of fungus within the division Basidiomycota. The subdivision contains 9 classes, 20 orders, and 37 families. Over 8400 species of Pucciniomycotina have been described - more than 8% of all described fungi. The subdivision is considered a sister group to Ustilaginomycotina and Agaricomycotina, which may share the basal lineage of Basidiomycota, although this is uncertain due to low support for placement between the three groups. The group was known as Urediniomycetes until 2006, when it was elevated from a class to a subdivision and named after the largest order in the group, Puccinales.

Pathogenic fungi are fungi that cause disease in humans or other organisms. Approximately 300 fungi are known to be pathogenic to humans. The study of fungi pathogenic to humans is called "medical mycology". Although fungi are eukaryotic, many pathogenic fungi are microorganisms. The study of fungi and other organisms pathogenic to plants is called plant pathology.

“Black yeasts”, sometimes also black fungi, dematiaceous fungi, microcolonial fungi or meristematic fungi is a diverse group of slow-growing microfungi which reproduce mostly asexually. Only few genera reproduce by budding cells, while in others hyphal or meristematic (isodiametric) reproduction is preponderant. Black yeasts share some distinctive characteristics, in particular melanisation of their cell wall. Morphological plasticity, incrustation of the cell wall with melanins and presence of other protective substances like carotenoids and mycosporines represent passive physiological adaptations which enable black fungi to be highly resistant against environmental stresses. The term "polyextremotolerance" has been introduced to describe this phenotype, a good example of which is the species Aureobasidium pullulans. Presence of 1,8-dihydroxynaphthalene melanin in the cell wall confers to the microfungi their characteristic olivaceous to dark brown/black colour.

The following outline is provided as an overview of and topical guide to fungi:

Aspergillus giganteus is a species of fungus in the genus Aspergillus that grows as a mold. It was first described in 1901 by Wehmer, and is one of six Aspergillus species from the Clavati section of the subgenus Fumigati. Its closest taxonomic relatives are Aspergillus rhizopodus and Aspergillus longivescia.

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