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 φυσα (physa), which means “blister” or “bubble” [4] , referring to the bubble-like appearance of its sporangia.
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]
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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]
There is no direct evidence showing that Physarum is infectious.
Media related to Physarum at Wikimedia Commons
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