| Polysphondylium pallidum | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Phylum: | Amoebozoa |
| Class: | Dictyostelia |
| Order: | Dictyosteliida |
| Family: | Dictyosteliidae |
| Genus: | Polysphondylium |
| Species: | P. pallidum |
| Binomial name | |
| Polysphondylium pallidum | |
Polysphondylium pallidum is a species of cellular slime mould, a member of the phylum Mycetozoa.
The lectotype of Polysphondylium pallidum was first described from Liberia where it was growing on the dung of an ass. [2] This slime mould has a world-wide distribution but there has been found to be variation between different samples and in a taxonomic revision in 2008, Kawakami and Hagiwara determined that some specimens originally described as P. pallidum were a different species, Polysphondylium album . [3]
Polysphondylium pallidum starts life as a single-celled amoeboid protist. Like other slime moulds, it lives in soil, dung, leaf litter and other decaying organic materials. It is known as a myxamoeba and feeds on bacteria and fungal spores. In favourable, damp conditions it may reproduce sexually while in drier conditions, asexual reproduction is more likely. The myxamoebae release a chemical agent, acrasin, which guides other slime mould cells to move towards them. [4] [5]
The myxoedemae of Polysphondylium pallidum were found to exist in two separate mating types in an early (1975) study on the species, [6] but a more recent morphological study left the question of the number of identifiable and separate mating types undecided.[ dubious ] [3] Under favourable damp conditions, a haploid cell with a single set of chromosomes will unite with another cell of opposite mating type to form a diploid cell, with a double complement of chromosomes. Other nearby amoeboid cells are absorbed into this diploid cell by phagocytosis to form a giant cell. This undergoes meiosis and becomes a large cyst in which spores are formed and later released to be dispersed by air movements. [7]
In damp weather, a Polysphondylium pallidum myxamoeba can move around at a speed of about 1 millimetre (0.04 in) per hour, leaving a chemical trail behind it. When it finds the trail left by another myxamoeba, it follows it, superimposing its own trace signal, and more and more individuals collect together in this way. Under favourable conditions, the myxamoebae agglutinate and stick together to form a "pseudoplasmodium" in which they remain separate individuals but behave as if the whole mass was a single organism. The pseudoplasmodium can move around and in due course develops into a fruiting body called a sporangium, about a third of the cells forming a stalk and the remaining cells forming a ball at the top where they develop into spores. The spores have a smooth wall containing cellulose, a material not found among fungi which have cell walls strengthened by chitin. As the ball dries out, the spores are dispersed by the wind. The myxamoebae that form the supporting stem die, having sacrificed themselves for the greater good. [5] [7]
Slime moulds are of interest to developmental biologists because they represent a link between single-celled organisms and multi-celled organisms. [4] In an experiment to study the conditions necessary for agglutination, Polysphondylium pallidum was cultured on plates of hay-infusion agar. A thin surface layer of Escherichia coli was added, created by allowing a drop of suspension to spread out over the surface of the non-nutrient agar to form a layer of even thickness. The myxamoebae were inoculated centrally on the plate. The culture was then incubated under different conditions of light and darkness and it was found that agglutination was greatly increased by exposure to light. Even one minute of illumination soon after incubation had started was sufficient to trigger multiple centres of agglutination. One minute of exposure at a later stage was less effective. [8] Although light was involved in agglutination, the introduction of some light exposed myxamoebae did not cause dark-only cells to clump. Other possible stimuli were tried but mostly had negative responses; heat was ineffective; CO2 had little effect but reduced clumping in light treated cells; potassium hydroxide had little effect; charcoal increased the number of clumps in light treated cells and caused a slight increase in number of dark cells that agglutinated; mineral oil has similar effects to charcoal in light treated cells but a more marked effect in the dark cells where the resulting aggregations nearly reached that found in light treated cultures. The conclusions drawn from these experiments were that some form of suppressor may accumulate in the vicinity of the myxamoebae preventing them from agglutinating. Light exposure encouraged agglutination before much suppressor was present. Charcoal and mineral oil increased agglutination by absorbing the suppressor. [8]
Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are microscopic; those in the Myxogastria form larger plasmodial slime molds visible to the naked eye. The slime mold life cycle includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic multicellular or multinucleate fruiting bodies that may be formed through aggregation or fusion; aggregation is driven by chemical signals called acrasins. Slime molds contribute to the decomposition of dead vegetation; some are parasitic.
A mold or mould is one of the structures that certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not all fungi form molds. Some fungi form mushrooms; others grow as single cells and are called microfungi.
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa. They were thought to have appeared as early as the mid-late Ordovician period as an adaptation of early land plants.
The dictyostelids or cellular slime molds are a group of slime molds or social amoebae.
Dictyostelium is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as "slime molds". They are present in most terrestrial ecosystems as a normal and often abundant component of the soil microflora, and play an important role in the maintenance of balanced bacterial populations in soils.
Physarum polycephalum, an acellular slime mold or myxomycete popularly known as "the blob", is a protist with diverse cellular forms and broad geographic distribution. The “acellular” moniker derives from the plasmodial stage of the life cycle: the plasmodium is a bright yellow macroscopic multinucleate coenocyte shaped in a network of interlaced tubes. This stage of the life cycle, along with its preference for damp shady habitats, likely contributed to the original mischaracterization of the organism as a fungus. P. polycephalum is used as a model organism for research into motility, cellular differentiation, chemotaxis, cellular compatibility, and the cell cycle.
Lycogala epidendrum, commonly known as wolf's milk or groening's slime, is a cosmopolitan species of myxogastrid amoeba which is often mistaken for a fungus. The aethalia, or fruiting bodies, occur either scattered or in groups on damp rotten wood, especially on large logs, from June to November. These aethalia are small, pink to brown cushion-like blobs. They may ooze a pink "paste" if the outer wall is broken before maturity. When mature, the colour tends to become more brownish. When not fruiting, single celled individuals move about as very small, red amoeba-like organisms called plasmodia, masses of protoplasm that engulf bacteria, as well as fungal and plant spores, protozoa, and particles of non-living organic matter through phagocytosis.
A grex starts as a crowd of single-celled amoebae of the groups Acrasiomycota or Dictyosteliida; grex is the Latin word for flock. The cells flock together, forming a mass that behaves as an organised, slug-like unit. Before they get stimulated to crowd together to form a grex, the amoebae simply wander as independent cells grazing on bacteria and other suitable food items. They continue in that way of life as long as conditions are favourable. When the amoebae are stressed, typically by a shortage of food, they form a grex.
Multinucleate cells are eukaryotic cells that have more than one nucleus per cell, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordinated, synchronous manner where all nuclei divide simultaneously or asynchronously where individual nuclei divide independently in time and space. Certain organisms may have a multinuclear stage of their life cycle. For example, slime molds have a vegetative, multinucleate life stage called a plasmodium.
Dictyostelium discoideum is a species of soil-dwelling amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, D. discoideum is a eukaryote that transitions from a collection of unicellular amoebae into a multicellular slug and then into a fruiting body within its lifetime. Its unique asexual life cycle consists of four stages: vegetative, aggregation, migration, and culmination. The life cycle of D. discoideum is relatively short, which allows for timely viewing of all stages. The cells involved in the life cycle undergo movement, chemical signaling, and development, which are applicable to human cancer research. The simplicity of its life cycle makes D. discoideum a valuable model organism to study genetic, cellular, and biochemical processes in other organisms.
Protosteliomycetes/Protosteliales (ICBN) or Protostelea/Protostelia/Protosteliida (ICZN) is a grouping of slime molds from the phylum Mycetozoa. The name can vary depending upon the taxon used. Other names include Protostelea, Protostelia, and Protostelida. When not implying a specific level of classification, the term protostelid or protosteloid amoeba is sometimes used.
Myxogastria/Myxogastrea or Myxomycetes (ICN) is a class of slime molds that contains 5 orders, 14 families, 62 genera, and 888 species. They are colloquially known as the plasmodial or acellular slime moulds.
A plasmodium is a living structure of cytoplasm that contains many nuclei, rather than being divided into individual cells each with a single nucleus.
Trichiales is an order of slime moulds in the phylum Amoebozoa. Trichiales is one of five orders in the group Myxomycetes, or the true plasmodial slime molds. It is also currently categorized under the superorder Lucisporidia with its sister group, Liceales. The order was first described by Thomas MacBride in 1922, and has retained the same name and status as a defined order in present phylogeny. In the plasmodium form, members of Trichiales lack a columella but have a well-developed capillitium for spore dispersal. The shape and details of the capillitium are used to define families within the order. Spores are brightly coloured, ranging from clear, white and yellow to pink and red-brown tones. The order currently has 4 families, 14 genera and 174 species. Recent molecular research has shown that while Trichiales probably represents a true taxonomic group, its sister group Liceales is likely paraphyletic, and it has been suggested that several genera from the Liceales should be reclassified under Trichiales instead.
Ceratiomyxa is a genus of plasmodial slime mould within the Eumycetozoa, first described by Pier Antonio Micheli. They are widely distributed and commonly found on decaying wood.
Fonticula is a genus of cellular slime mold which forms a fruiting body in a volcano shape. As long ago as 1979 it has been known to not have a close relationship with either the Dictyosteliida or the Acrasidae, the two well-established groups of cellular slime molds. In 1979, Fonticula was made a new genus of its own due to the unique characteristics of its fruiting body, with only one species: Fonticula alba.
Enteridium lycoperdon, the false puffball, is one of the more obvious species of slime mould or Myxogastria, typically seen in its reproductive phase as a white 'swelling' on standing dead trees in the spring, or on large pieces of fallen wood. Alder is a common host.
An amoeba, often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, and animals.
Hemitrichia is a genus of slime molds, of the family Trichiidae, found within the order Trichiida. It was first described by Josef Rostafinski in 1873 and remains a well-defined genus of the slime molds. Hemitrichia species exhibit either plasmodiocarp or sporangium fruiting bodies, both of which are well-known and recognizable slime molds seen on multiple continents. The genus includes Hemtrichia serpula, known as the pretzel slime mold, an iconic and widespread species that has been used to examine speciation in slime molds.
Trichia crateriformis is a slime mold species in the order Trichiida found in temperate areas throughout the world.