Physarum

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Physarum is the largest genus of mycetozoan slime molds in the family Physaraceae.[2] They typically thrive in cool, dark, and humid environments, including the bark of trees (often where moss is present), dead twigs, rotting logs covered with moss, leaf litter, and moist forest soils.[3] The name Physarum comes from the Greek word Script error: No such module "Lang". (physa), which means "blister" or "bubble",[4] referring to the bubble-like appearance of its sporangia.

Phylogeny

Physarum is classified not as a fungus, but as a slime mold belonging to the Amoebozoa. Phylogenetic studies of Unikonts indicate that acellular slime molds like Physarum are related to cellular slime molds such as Dictyostelium, as well as other members of the Amoebozoa.[5]

Analyses of ribosomal DNA (rDNA) sequences show that Physarum is polyphyletic, forming at least three distinct clades. Support for the polyphyletic origin of Physarum comes from a synapomorphy: the highly conserved G-binding site of L2449 group I intron ribozymes.[6]

File:Nandipati et al. 2012 BMC Evol. Biol.-Fig2.webp
Maximum-Likelihood phylogenetic tree of Physarales isolates based on the combined SSU/LSU data set
File:Nandipati et al. 2012 BMC Evol. Biol.-Fig4.webp
RNA structure diagrams of L2449 group I introns in Physarales clades

Life cycle

Physarum’s life cycle alternates between a haploid unicellular stage (amoeboid or flagellated cells) and a diploid multinucleate stage (plasmodium). Under favorable conditions, mature sporangia release spores that germinate into amoeboid cells. In dry environments, these cells form dormant microcysts capable of withstanding dehydration and nutrient scarcity, remaining viable until conditions improve, at which point they revive into active amoebae. Conversely, in excessively wet conditions, cells develop flagella and transition to a free-swimming form.

Cell fusion (syngamy or fertilization) between compatible cells gives rise to the multinucleate plasmodium. Under adverse conditions, such as desiccation, low temperature, or nutrient limitation, the plasmodium transforms into a hardened structure called a sclerotium, which remains dormant until conditions become favorable. When environmental conditions permit, the mature plasmodium forms sporangia, where spores are produced through meiosis. The release of these spores marks the start of a new life cycle.[7]

File:Physarum developmental cycle and cellular organization.gif
Physarum developmental cycle and cellular organization

References

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  1. ^ Unit Prot Taxonomy Genus Physarum
  2. ^ Page Module:Citation/CS1/styles.css has no content.Leontyev, Dmitry V.; Schnittler, Martin; Stephenson, Steven L.; Novozhilov, Yuri K.; Shchepin, Oleg N. (2019). "Towards a phylogenetic classification of the Myxomycetes". Phytotaxa. 399 (3): 209. Bibcode:2019Phytx.399..209L. doi:10.11646/phytotaxa.399.3.5. ISSN 1179-3163. S2CID 108783142.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Glime, J. M. (2019). Slime Molds: Ecology and Habitats – Bark and Logs. Chapt. 3-3. In: Glime, J. M. Bryophyte Ecology. Volume 2. Bryological Interaction.
  4. ^ Page Module:Citation/CS1/styles.css has no content.Kluge, F. (1967). Etymologisches Wörterbuch der deutschen Sprache.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Miller, Dennis; Padmanabhan, Ramesh; Sarcar, Subha N. (2017). "Genomics and Gene Expression in Myxomycetes". Myxomycetes: Biology, Systematics, Biogeography, and Ecology. Chapter 4-Genomics and Gene Expression in Myxomycetes. Elsevier Inc. pp. 107–143. doi:10.1016/B978-0-12-805089-7.00004-4.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Nandipati, S.C.; Haugli, K.; Coucheron, D.H.; Haskins, E.F .; Johansen, S.D. (2012). "Polyphyletic origin of the genus Physarum (Physarales, Myxomycetes) revealed by nuclear rDNA mini-chromosome analysis and group I intron synapomorphy". BMC Evol. Biol. 12 (1) 166. Bibcode:2012BMCEE..12..166N. doi:10.1186/1471-2148-12-166. PMC 3511172.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Le Verge-Serandour, M.; Alim, K. (2024). "Physarum polycephalum: Smart Network Adaptation". Annu. Rev. Condens. Matter Phys. 15: 263-289. doi:10.1146/annurev-conmatphys-040821-115312.

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