Conidium

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Conidia on conidiophores Conidium.png
Conidia on conidiophores
Chain of conidia of Alternaria Chain of conidia of an Alternaria sp. fungus PHIL 3963 lores.jpg
Chain of conidia of Alternaria
Conidiomata of Cypress canker (probably Seiridium cardinale) erupting on a Thuja twig Seiridium canker 100814w.JPG
Conidiomata of Cypress canker (probably Seiridium cardinale) erupting on a Thuja twig

A conidium ( /kəˈnɪdiəm,koʊ-/ kə-NID-ee-əm, koh-; pl.: conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (pl.: chlamydoconidia), [1] is an asexual, [2] non-motile spore of a fungus. The word conidium comes from the Ancient Greek word for dust, κόνις (kónis). [3] They are also called mitospores due to the way they are generated through the cellular process of mitosis.[ citation needed ] They are produced exogenously. 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.

Contents

Asexual reproduction in ascomycetes (the phylum Ascomycota) is by the formation of conidia, which are borne on specialized stalks called conidiophores. The morphology of these specialized conidiophores is often distinctive between species and, before the development of molecular techniques at the end of the 20th century, was widely used for identification of (e.g. Metarhizium ) species.

The terms microconidia and macroconidia are sometimes used. [4]

Conidiogenesis

There are two main types of conidium development: [5]

Conidia germination

A conidium may form germ tubes (germination tubes) and/or conidial anastomosis tubes (CATs) in specific conditions. These two are some of the specialized hyphae that are formed by fungal conidia. The germ tubes will grow to form the hyphae and fungal mycelia. The conidial anastomosis tubes are morphologically and physiologically distinct from germ tubes. After conidia are induced to form conidial anastomosis tubes, they grow homing toward each other, and they fuse. Once fusion happens, the nuclei can pass through fused CATs. These are events of fungal vegetative growth and not sexual reproduction. Fusion between these cells seems to be important for some fungi during early stages of colony establishment. The production of these cells has been suggested to occur in 73 different species of fungi. [6] [7]

Germination in Aspergillus

As evidenced by recent literature, conidia germination of Aspergillus, a common mold, specifically is of interest. Aspergillus is not only a familiar fungus found across various different settings in the world, but it poses a danger for immunocompromised individuals, as inhaled Aspergillus conidia could germinate inside the respiratory tract and cause aspergillosis, a form of pulmonary infection, and continual developments of aspergillosis such as new risk groups and the resistance against antifungal drugs.

Stages of Germination: Dormancy

Germination in Aspergillus follows a sequence of three different stages: dormancy, isotropic growth, and polarized growth. The dormant conidia are able to germinate even after an year of remaining at room temperature, due to their resilient intracellular and extracellular characteristics, which enable them to undergo harsh conditions like dehydration, variation in osmotic pressure, oxidation, and temperature, and change in UV exposure and acidity levels. These abilities of the dormant conidia are dictated by a few central regulatory proteins, which are the main drivers of the conidia and conidiophore formation. One of these proteins, the developmental regulatory protein wetA, has been found to be particularly essential; in wetA-defective mutants have reduced tolerance to external factors mentioned above, and exhibit weak synthesization of the conidial cell wall. In addition to these central regulators, some notable groups of genes/proteins include other regulatory proteins like the velvet regulator proteins, which contribute to fungal growth, and other molecules that target specific unfavorable intra and extracellular conditions, like heat shock proteins. [8] [9]

Stages of Germination: Isotropic and Polarized Growth

The phases following dormancy include isotropic growth, in which increased intracellular osmotic pressure and water uptake causes swelling of the conidia and increased cellular diameter, and polarized growth, in which the swelling from isotropic growth directs the growth to one side of the cell, and leads to the formation of a germ tube. First, however, the conidia must go through the stage of breaking dormancy. In some species of Aspergillus, dormancy is broken when the dormant conidia is introduced to a carbon source in the presence of water and air, while in other species, the mere presence of glucose is enough to trigger it. The dense outer layer of the dormant conidia is shed and the growth of the hyphae cells begins, which has a significantly different composition compared to the dormant conidia cell. Breaking of dormancy involves transcription, but not translation; protein synthesis inhibitors prevent isotropic growth, while DNA and RNA synthesis inhibitors do not, and the start of breaking of dormancy is accompanied by and increase in transcripts for genes for biosynthesis of proteins, and immediate protein synthesis. Following the expansion of the cell via isotropic growth, studies have observed many new proteins emerging from the processes in the breaking of dormancy and transcripts associated with remodeling of the cell wall, suggesting that remodeling of the cell wall is a central process during isotropic growth. In the polarized growth stage, upregulated and overexpressed proteins and transcripts included ones involved in synthesis of chitin (a major component of the fungal cell wall), mitosis and DNA processing, remodeling of cell morphology, and ones in germ tube formation pertaining to infection and virulence factors. [8] [9]

Structures for release of conidia

Conidiogenesis is an important mechanism of spread of plant pathogens. In some cases, specialized macroscopic fruiting structures perhaps 1 mm or so in diameter containing masses of conidia are formed under the skin of the host plant and then erupt through the surface, allowing the spores to be distributed by wind and rain. One of these structures is called a conidioma (plural: conidiomata). [10] [11]

Two important types of conidiomata, distinguished by their form, are:

Pycnidial conidiomata or pycnidia form in the fungal tissue itself, and are shaped like a bulging vase. The conidia are released through a small opening at the apex, the ostiole.

Acervular conidiomata, or acervuli, are cushion-like structures that form within the tissues of a host organism:

Mostly they develop a flat layer of relatively short conidiophores which then produce masses of spores. The increasing pressure leads to the splitting of the epidermis and cuticle and allows release of the conidia from the tissue.

Health issues

Conidia are always present in the air, but levels fluctuate from day to day and with the seasons. An average person inhales at least 40 conidia per hour. [12] Exposure to conidia from certain species, such as those of Cryptostroma corticale , is known to cause hypersensitivity pneumonitis, an occupational hazard for forest workers and paper mill employees. [13] [14]

Conidia are often the method by which some normally harmless but heat-tolerating (thermotolerant), common fungi establish infection in certain types of severely immunocompromised patients (usually acute leukemia patients on induction chemotherapy, AIDS patients with superimposed B-cell lymphoma, bone marrow transplantation patients (taking immunosuppressants), or major organ transplant patients with graft versus host disease). Their immune system is not strong enough to fight off the fungus, and it may, for example, colonise the lung, resulting in a pulmonary infection. [15] Especially with species of the Aspergillus genus, germination in the respiratory tract can lead to aspergillosis, which is quite common, can vary in severity, and has shown signs of developing new risk groups and antifungal drug resistance. [8]

See also

Related Research Articles

<span class="mw-page-title-main">Ascomycota</span> Division or phylum of fungi

Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms 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 Ascomycota are asexual and thus do not form asci or ascospores. Familiar examples of sac fungi include morels, truffles, brewers' and bakers' yeast, dead man's fingers, and cup fungi. The fungal symbionts in the majority of lichens such as Cladonia belong to the Ascomycota.

<span class="mw-page-title-main">Germination</span> Process by which an organism grows from a spore or seed

Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ferns, bacteria, and the growth of the pollen tube from the pollen grain of a seed plant.

<i>Aspergillus flavus</i> Species of fungus

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. Its specific name flavus derives from the Latin meaning yellow, a reference to the frequently observed colour of the spores. A. flavus infections can occur while hosts are still in the field (preharvest), but often show no symptoms (dormancy) until postharvest storage 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.

<i>Aspergillus fumigatus</i> Species of fungus

Aspergillus fumigatus is a species of fungus in the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in individuals with an immunodeficiency.

<i>Aspergillus terreus</i> Species of fungus

Aspergillus terreus, also known as Aspergillus terrestris, is a fungus (mold) found worldwide in soil. Although thought to be strictly asexual until recently, A. terreus is now known to be capable of sexual reproduction. This saprotrophic fungus is prevalent in warmer climates such as tropical and subtropical regions. Aside from being located in soil, A. terreus has also been found in habitats such as decomposing vegetation and dust. A. terreus is commonly used in industry to produce important organic acids, such as itaconic acid and cis-aconitic acid, as well as enzymes, like xylanase. It was also the initial source for the drug mevinolin (lovastatin), a drug for lowering serum cholesterol.

<i>Colletotrichum lindemuthianum</i> Species of fungus

Colletotrichum lindemuthianum is a fungus which causes anthracnose, or black spot disease, of the common bean plant. It is considered a hemibiotrophic pathogen because it spends part of its infection cycle as a biotroph, living off of the host but not harming it, and the other part as a necrotroph, killing and obtaining nutrients from the host tissues.

Nigrospora sphaerica is an airborne filamentous fungus in the phylum Ascomycota. It is found in soil, air, and plants as a leaf pathogen. It can occur as an endophyte where it produces antiviral and antifungal secondary metabolites. Sporulation of N. sphaerica causes its initial white coloured colonies to rapidly turn black. N. sphaerica is often confused with the closely related species N. oryzae due to their morphological similarities.

Conidial anastomosis tubes (CATs) are cells formed from the conidia of many filamentous fungi. These cells have a tubular shape and form an anastomosis (bridge) that allows fusion between conidia.

Aspergillus ochraceus is a mold species in the genus Aspergillus known to produce the toxin ochratoxin A, one of the most abundant food-contaminating mycotoxins, and citrinin. It also produces the dihydroisocoumarin mellein. It is a filamentous fungus in nature and has characteristic biseriate conidiophores. Traditionally a soil fungus, has now began to adapt to varied ecological niches, like agricultural commodities, farmed animal and marine species. In humans and animals the consumption of this fungus produces chronic neurotoxic, immunosuppressive, genotoxic, carcinogenic and teratogenic effects. Its airborne spores are one of the potential causes of asthma in children and lung diseases in humans. The pig and chicken populations in the farms are the most affected by this fungus and its mycotoxins. Certain fungicides like mancozeb, copper oxychloride, and sulfur have inhibitory effects on the growth of this fungus and its mycotoxin producing capacities.

Aspergillus penicillioides is a species of fungus in the genus Aspergillus, and is among the most xerophilic fungi.

<i>Aspergillus candidus</i> Species of fungus

Aspergillus candidus is a white-spored species of fungus in the genus Aspergillus. Despite its lack of pigmentation, it is closely related to the most darkly-pigmented aspergilli in the Aspergillus niger group. It is a common soil fungus worldwide and is known as a contaminant of a wide array of materials from the indoor environment to foods and products. It is an uncommon agent of onychomycosis and aspergillosis. The species epithet candidus (L.) refers to the white pigmentation of colonies of this fungus. It is from the Candidi section. The fungi in the Candidi section are known for their white spores. It has been isolated from wheat flour, djambee, and wheat grain.

<i>Penicillium digitatum</i> Species of fungus

Penicillium digitatum is a mesophilic fungus found in the soil of citrus-producing areas. It is a major source of post-harvest decay in fruits and is responsible for the widespread post-harvest disease in Citrus fruit known as green rot or green mould. In nature, this necrotrophic wound pathogen grows in filaments and reproduces asexually through the production of conidiophores and conidia. However, P. digitatum can also be cultivated in the laboratory setting. Alongside its pathogenic life cycle, P. digitatum is also involved in other human, animal and plant interactions and is currently being used in the production of immunologically based mycological detection assays for the food industry.

<i>Aspergillus clavatus</i> Species of fungus

Aspergillus clavatus is a species of fungus in the genus Aspergillus with conidia dimensions 3–4.5 x 2.5–4.5 μm. It is found in soil and animal manure. The fungus was first described scientifically in 1834 by the French mycologist John Baptiste Henri Joseph Desmazières.

<i>Penicillium spinulosum</i> Species of fungus

Penicillium spinulosum is a non-branched, fast-growing fungus with a swelling at the terminal of the stipe (vesiculate) in the genus Penicillium. P. spinulosum is able to grow and reproduce in environment with low temperature and low water availability, and is known to be acidotolerant. P. spinulosum is ubiquitously distributed, and can often be isolated from soil. Each individual strain of P. spinulosum differs from others in their colony morphology, including colony texture, amount of sporulation and roughness of conidia and conidiophores.

Aspergillus wentii is an asexual, filamentous, endosymbiotic fungus belonging to the mold genus, Aspergillus. It is a common soil fungus with a cosmopolitan distribution, although it is primarily found in subtropical regions. Found on a variety of organic materials, A. wentii is known to colonize corn, cereals, moist grains, peanuts and other ground nut crops. It is also used in the manufacture of biodiesel from lipids and is known for its ability to produce enzymes used in the food industry.

<i>Alternaria brassicicola</i> Species of fungus

Alternaria brassicicola is a fungal necrotrophic plant pathogen that causes black spot disease on a wide range of hosts, particularly in the genus of Brassica, including a number of economically important crops such as cabbage, Chinese cabbage, cauliflower, oilseeds, broccoli and canola. Although mainly known as a significant plant pathogen, it also contributes to various respiratory allergic conditions such as asthma and rhinoconjunctivitis. Despite the presence of mating genes, no sexual reproductive stage has been reported for this fungus. In terms of geography, it is most likely to be found in tropical and sub-tropical regions, but also in places with high rain and humidity such as Poland. It has also been found in Taiwan and Israel. Its main mode of propagation is vegetative. The resulting conidia reside in the soil, air and water. These spores are extremely resilient and can overwinter on crop debris and overwintering herbaceous plants.

Microascus manginii is a filamentous fungal species in the genus Microascus. It produces both sexual (teleomorph) and asexual (anamorph) reproductive stages known as M. manginii and Scopulariopsis candida, respectively. Several synonyms appear in the literature because of taxonomic revisions and re-isolation of the species by different researchers. M. manginii is saprotrophic and commonly inhabits soil, indoor environments and decaying plant material. It is distinguishable from closely related species by its light colored and heart-shaped ascospores used for sexual reproduction. Scopulariopsis candida has been identified as the cause of some invasive infections, often in immunocompromised hosts, but is not considered a common human pathogen. There is concern about amphotericin B resistance in S. candida.

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.

<span class="mw-page-title-main">Glossary of mycology</span>

This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found in glossary of biology and glossary of botany, among others. List of Latin and Greek words commonly used in systematic names and Botanical Latin may also be relevant, although some prefixes and suffixes very common in mycology are repeated here for clarity.

Meristacrum is a fungal genus in the monotypic family Meristacraceae, of the order Entomophthorales. They are parasites of soil invertebrates, they typically infect nematodes, and tardigrades.

References

  1. ↑ Jansonius, D.C., Gregor, Me., 1996. Palynology: principles and applications. American association of stratigraphic palynologists foundation.[ page needed ]
  2. ↑ Osherov, Nir; May, Gregory S (2001). "The molecular mechanisms of conidial germination". FEMS Microbiology Letters. 199 (2): 153–60. doi: 10.1111/j.1574-6968.2001.tb10667.x . PMID   11377860.
  3. ↑ "conidium". CollinsDictionary.com . HarperCollins.
  4. ↑ Ohara, T.; Inoue, I; Namiki, F; Kunoh, H; Tsuge, T (2004). "REN1 is Required for Development of Microconidia and Macroconidia, but Not of Chlamydospores, in the Plant Pathogenic Fungus Fusarium oxysporum". Genetics. 166 (1): 113–24. doi:10.1534/genetics.166.1.113. PMC   1470687 . PMID   15020411.
  5. ↑ Sigler, Lynne (1989). "Problems in application of the terms 'blastic' And 'thallic' To modes of conidiogenesis in some onygenalean fungi". Mycopathologia. 106 (3): 155–61. doi:10.1007/BF00443056. PMID   2682248. S2CID   8218393.
  6. ↑ Friesen, Timothy L; Stukenbrock, Eva H; Liu, Zhaohui; Meinhardt, Steven; Ling, Hua; Faris, Justin D; Rasmussen, Jack B; Solomon, Peter S; McDonald, Bruce A; Oliver, Richard P (2006). "Emergence of a new disease as a result of interspecific virulence gene transfer". Nature Genetics. 38 (8): 953–6. doi:10.1038/ng1839. PMID   16832356. S2CID   6349264.
  7. ↑ Gabriela Roca, M.; Read, Nick D.; Wheals, Alan E. (2005). "Conidial anastomosis tubes in filamentous fungi". FEMS Microbiology Letters. 249 (2): 191–8. doi: 10.1016/j.femsle.2005.06.048 . PMID   16040203.
  8. 1 2 3 Baltussen, Tim J. H.; Zoll, Jan; Verweij, Paul E.; Melchers, Willem J. G. (2020-02-19). "Molecular Mechanisms of Conidial Germination in Aspergillus spp". Microbiology and Molecular Biology Reviews. 84 (1). doi:10.1128/MMBR.00049-19. ISSN   1092-2172. PMC   6903801 . PMID   31801804.
  9. 1 2 Osherov, Nir (2014-04-09), Latgé, Jean-Paul; Steinbach, William J. (eds.), "Conidial Germination in Aspergillus fumigatus", Aspergillus fumigatus and Aspergillosis, Washington, DC, USA: ASM Press, pp. 131–142, doi:10.1128/9781555815523.ch10, ISBN   978-1-68367-138-1 , retrieved 2024-05-11
  10. ↑ James J. Worrall (2023). "Fungi". Forest Pathology. Retrieved 20 February 2023.
  11. ↑ d'Arcy, C.J.; Eastburn, D.M.; Schumann, G.L. (2001). "Illustrated Glossary of Plant Pathology". The Plant Health Instructor. doi:10.1094/PHI-I-2001-0219-01.
  12. ↑ Humans inhale ~103 to 1010 mold conidia (i.e., vegetative spores) daily. - Shlezinger, Neta; Irmer, Henriette; Dhingra, Sourabh; Beattie, Sarah R.; Cramer, Robert A.; Braus, Gerhard H.; Sharon, Amir; Hohl, Tobias M. (8 Sep 2017). "Sterilizing immunity in the lung relies on targeting fungal apoptosis-like programmed cell death". Science. 357 (6355): 1037–1041. Bibcode:2017Sci...357.1037S. doi: 10.1126/science.aan0365 . PMC   5628051 . PMID   28883073.
  13. ↑ Worrall, James J. (2023). "Sooty-Bark Disease of Maple". Forest Pathology. Retrieved 18 February 2023.
  14. ↑ Braun, Markus; Klingelhöfer, Doris; Groneberg, David A. (2021). "Sooty bark disease of maples: the risk for hypersensitivity pneumonitis by fungal spores not only for woodman". Journal of Occupational Medicine and Toxicology. 16 (1): 2. doi: 10.1186/s12995-021-00292-5 . PMC   7819180 . PMID   33478566. 2.
  15. ↑ Of particular concern is the high rate of mortality associated with invasive fungal infections, which often exceeds 50% despite the availability of several antifungal drugs. - Brown, Gordon D.; Denning, David W.; Gow, Neil A. R.; Levitz, Stuart M.; Netea, Mihai G.; White, Theodore C. (19 December 2012). "Hidden Killers: Human Fungal Infections". Sci Transl Med. 4 (165 165rv13): 165rv13. doi:10.1126/scitranslmed.3004404. PMID   23253612. S2CID   3157271.
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