Acrasidae

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Acrasid slime molds
Acrasis rosea 31095.jpg
Acrasis rosea
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Discoba
Superphylum: Discicristata
Phylum: Percolozoa
Class: Heterolobosea
Order: Acrasida
Family: Acrasidae
van Tieghem 1880 ex Hartog 1906
Genera
Synonyms
  • Acrasiaceae Poche 1913 em. Olive 1970
  • Guttulinaceae Zopf 1885 ex Berlese 1888 nom. rej.
  • Guttulininae Doflein & Reichenow 1952
  • Pocheinaceae Loeblich & Tappan 1961 nom. cons.
Acrasis rosea amoebae and spores under microscope Acrasis rosea 31330.jpg
Acrasis rosea amoebae and spores under microscope

The family Acrasidae (ICZN, or Acrasiomycota, ICBN) is a family [1] of slime molds which belongs to the excavate group Percolozoa. The name element acrasio- comes from the Greek akrasia , meaning "acting against one's judgement". This group consists of cellular slime molds.

The terms "Acrasiomycota" or "Acrasiomycetes" have been used when the group was classified as a fungus ("-mycota"). In some classifications, Dictyostelium was placed in Acrasiomycetes, an artificial group of cellular slime molds, which was characterized by the aggregation of individual amoebae into a multicellular fruiting body, making it an important factor that related the acrasids to the dictyostelids. [2]

Each cell keeps its individuality even when it forms a stalk and fruiting body to reproduce. [3] Slime molds were originally thought to be in a monophyletic group Mycetozoa, with little distinction between Acrasis and Dictyostelids, however scientists uncovered that they were distinct groups, and eventually that Acrasis was incredibly distant on the tree of life. Instead, it is found in Heterolobosia with Naegleria, away from other myxamoeba. [4]

Ecology

Acrasis is found in terrestrial habitats on dead or decaying bark or dead tissue still attached to plants. [3] They are often cultured using yeast which makes up most of their diet, but they are known to participate in cannibalism in their solitary mobile stage of life. [5] They may also be found on living tree bark. [3]

Evolutionary History

Historically it was thought that Acrasis was a sister group to Dictyostilids, other slime mold amoebas that belong to Amoebazoa, due to how they both aggregate in order to form a fruiting body. However, in their amoeboid form it was realized they were fundamentally different and molecular phylogenetic studies placed Acrasis in Heterolobosea with the brain-eating amoebae Naegleria fowleri. [6] One particular morphological difference between Acrasis and Dictyostilids is that the stalks of the fruiting body in Acrasis are trunk like and do not contain a cellulose sheath. [5]

Heterolobosea belong within Discoba which belongs within Excavata. Out of all Discobids, Acrasis has the most compact mitochondrial genome that requires additional transport activity due to the number of genes lost. tRNA genes, which are commonly found in most mitochondria sequences, are scarce in Acrasis and require transportation in for the translation of the remaining mitochondrial genes. The reason for this gene deficiency is because of lateral genetic transfer from the mitochondria to the nucleus. What is uncommon is how recently this phenomenon occurred in the Acrasis lineage, as sequence comparisons indicate lateral gene transfer after Acrasis split with Naglaeria. This has rarely been found in any other living species of Eukarya including Naglaeria, as most transfers between the mitochondria and nucleus happened in early endosymbiosis of mitochondrial ancestor into the ancestor of all Eukarya. [6]

Reproduction

When resources such as water or food become limiting, the amoeba will release pheromones such as acrasin to aggregate amoebal cells in preparation for movement as a large (thousands of cells) grex or pseudopod. When in the grex, the amoeboids reproduce, resulting in fruit-like structures called spores, which develop into unicellular molds of the same species.

Its reproductive cycle can be broken up to three distinct life stages where the Acrasis cell experiences morphological and intracellular changes [2].

Vegetative/Solitary Stage

After Acrasis spores are released, they germinate into free living limax amoebae, where they use a single pseudopodium to move forward, reaching to become up to 32 micrometers long. [3] During this stage they may experience conditions of starvation or dehydration where they differentiate into a microcyst that has an extracellular cell wall. [5] This microcyst can then differentiate back into the limax amoebae form. Alternatively, if conditions are favorable, a stimulus can signal the amoebae to aggregate together. [5]

Pseudoplasmodial Stage

Upon stimulation they begin to aggregate into the “slug” that will eventually begin to form a mound with others of the same species. [3]  [5]  Each cell keeps its individuality and only minor intracellular alterations are seen. [5]  One of the alterations seen in the cells between the vegetative and pseudoplasmodial stage is the decrease in number and volume of food vacuoles. 

Differientiated Stage

Within the mound one amoeba differentiates into a stalk cell that the others rest atop of, creating a structure called the sorogen. After the stalk grows from repeated cell differentiation into basal stalk cells, select cells form distal spore cells and the sporocarp structure from which they are released. This forms the fruiting body that overall has great plasticity through the ability to branch. [3] Throughout this process from the solitary stage to the formation of the fruiting body, each cell maintains its individuality. Following the formation of the fruiting body, spores are released, and the cycle begins anew. [5]

Related Research Articles

<span class="mw-page-title-main">Percolozoa</span> Phylum of Excavata

The Percolozoa are a group of colourless, non-photosynthetic Excavata, including many that can transform between amoeboid, flagellate, and cyst stages.

<span class="mw-page-title-main">Nucleariida</span> Order of amoebae

Nucleariida is a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid cristae, in the absence of superficial granules, and in the way they consume food.

<span class="mw-page-title-main">Slime mold</span> Spore-forming organisms

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.

<span class="mw-page-title-main">Excavata</span> Supergroup of unicellular organisms belonging to the domain Eukaryota

Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.

<span class="mw-page-title-main">Dictyostelid</span> Group of slime moulds

The dictyostelids or cellular slime molds are a group of slime molds or social amoebae.

<span class="mw-page-title-main">Mycetozoa</span> Infraphylum of protists

Mycetozoa is a polyphyletic grouping of slime molds. It was originally thought to be a monophyletic clade, but recently it was discovered that protostelia are a polyphyletic group within Conosa.

<i>Dictyostelium</i> Genus of slime molds

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.

<span class="mw-page-title-main">Amoebozoa</span> Phylum of protozoans

Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda.

<i>Naegleria</i> Genus of protists

Naegleria is a free living amoebae protist genus consisting of 47 described species often found in warm aquatic environments as well as soil habitats worldwide. It has three life cycle forms: the amoeboid stage, the cyst stage, and the flagellated stage, and has been routinely studied for its ease in change from amoeboid to flagellated stages. The Naegleria genera became famous when Naegleria fowleri, a human pathogenic strain and the causative agent of primary amoebic meningoencephalitis (PAM), was discovered in 1965. Most species in the genus, however, are nonpathogenic, meaning they do not cause disease.

<span class="mw-page-title-main">Lobosa</span> Phylum of protozoans

Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered Sapocribrum, has slender and threadlike (filose) pseudopodia. In current classification schemes, Lobosa is a subphylum, composed mainly of amoebae that have lobose pseudopods but lack cilia or flagella.

<i>Physarum polycephalum</i> Species of slime mold, model organism

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.

<span class="mw-page-title-main">Eumycetozoa</span> Taxonomic group of slime molds

Eumycetozoa, or true slime molds, is a diverse group of protists that behave as slime molds and develop fruiting bodies, either as sorocarps or as sporocarps. It is a monophyletic group or clade within the phylum Amoebozoa that contains the myxogastrids, dictyostelids and protosporangiids.

<span class="mw-page-title-main">Grex (biology)</span>

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.

<i>Dictyostelium discoideum</i> Species of slime mould

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.

<i>Naegleria gruberi</i> Species of protist

Naegleria gruberi is a species of Naegleria. It is famous for its ability to change from an amoeba, which lacks a cytoplasmic microtubule cytoskeleton, to a flagellate, which has an elaborate microtubule cytoskeleton, including flagella. This "transformation" includes de novo synthesis of basal bodies.

<span class="mw-page-title-main">Protosteliales</span> Group of slime moulds

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.

<span class="mw-page-title-main">Amoeboid movement</span> Mode of locomotion in eukaryotic cells

Amoeboid movement is the most typical mode of locomotion in adherent eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia ("false-feet") and posterior uropods. One or more pseudopodia may be produced at a time depending on the organism, but all amoeboid movement is characterized by the movement of organisms with an amorphous form that possess no set motility structures.

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.

<span class="mw-page-title-main">Amoeba</span> Cellular body type

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.

<i>Syssomonas</i> Genus of protists

Syssomonas is a monotypic genus of unicellular flagellated protists containing the species Syssomonas multiformis. It is a member of Pluriformea inside the lineage of Holozoa, a clade containing animals and their closest protistan relatives. It lives in freshwater habitats. It has a complex life cycle that includes unicellular amoeboid and flagellated phases, as well as multicellular aggregates, depending on the growth medium and nutritional state.

References

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  2. Cavender J.C.; Spiegl F.; Swanson A. (2002). "Taxonomy, slime molds, and the questions we ask". The Mycological Society of America. 94 (6): 968–979. PMID   21156570.
  3. 1 2 3 4 5 6 Brown, M. W.; Silberman; Spiegel (2010). "A Morphologically Simple Species of Acrasis (Heterolobosea, Excavata), Acrasis helenhemmesae n. sp". Journal of Eukaryotic Microbiology. 57 (4): 346–353. doi:10.1111/j.1550-7408.2010.00481.x. PMID   20497285.
  4. Brown, M. W.; Kolisko, M.; Silberman, J. D.; Roger, A. J. (2012). "Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria". Current Biology. 22 (12): 1123–1127. Bibcode:2012CBio...22.1123B. doi:10.1016/j.cub.2012.04.021. PMID   22608512.
  5. 1 2 3 4 5 6 7 Hohl, H. R.; Hamamoto, S. T. (1969). "Ultrastructure of Acrasis rosea, a Cellular Slime Mold, During Development*". The Journal of Protozoology. 16 (2): 333–344. doi:10.1111/j.1550-7408.1969.tb02279.x. PMID   5816073.
  6. 1 2 Fu, C. J.; Sheikh, S.; Miao, W.; Siv, G. E.; Andersson; Baldauf, S. L. (2014). "Missing Genes, Multiple ORFs, and C-to-U Type RNA Editing in Acrasis kona (Heterolobosea, Excavata) Mitochondrial DNA". Genome Biology and Evolution. 6 (9): 2240–2257. doi:10.1093/gbe/evu180. PMID   25146648.

Further reading