SLIME MOLD BLOG
Greendale School PROJECT REASERCH
slime mold
Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms that can live freely as single cells, but can aggregate together to form multicellular reproductive structures. Slime molds were formerly classified as fungi but are no longer considered part of that kingdom. Although not forming a single monophyletic clade, they are grouped within the paraphyletic group referred to as kingdom Protista.
More than 900 species of slime mold occur globally. Their common name refers to part of some of these organisms' life cycles where they can appear as gelatinous "slime".
This is mostly seen with the Myxogastria, which are the only macroscopic slime molds.Most slime molds are smaller than a few centimeters, but some species may reach sizes up to several square meters and masses up to 20 kilograms.Many slime molds, mainly the "cellular" slime molds, do not spend most of their time in this state. When food is abundant, these slime molds exist as single-celled organisms. When food is in short supply, many of these single-celled organisms will congregate and start moving as a single body. In this state they are sensitive to airborne chemicals and can detect food sources. They can readily change the shape and function of parts, and may form stalks that produce fruiting bodies, releasing countless spores, light enough to be carried on the wind or hitch a ride on passing animals.
What these three groups have in common is a life cycle that superficially resembles that of the fungi. When conditions become unfavorable, these slime molds form sporangia - clusters of spores, often on the tips of stalks such as in the sporangium of a Physarum shown at right. Spores from the sporangia are dispersed to new habitats, "germinate" into small amoebae, and the life cycle begins again. Similarities in the life cycle do not, however, imply close relationship, especially when one considers that certain bacteria (the myxobacteria) and even an unusual ciliate have very similar life cycles, aggregating to form spores on a sporangium.
Slime molds have almost no fossil record, which is not surprising. Not only do slime molds produce few resistant structures (except for spores, which are often overlooked or unidentifiable), but they live in moist terrestrial habitats, such as on decaying wood or fresh cow dung, where their potential for preservation is low. A few fossil slime molds have been found in amber (Poinar and Waggoner, 1992).
RESEARCH DATA
Slime mold
initial stage
Experiment Album
Daily
recording
Experimental data
Older classification
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Older classification[edit]
Slime molds, as a group, are polyphyletic. They were originally represented by the subkingdom Gymnomycota in the Fungi kingdom and included the defunct phyla Myxomycota, Acrasiomycota, and Labyrinthulomycota. Today, slime molds have been divided among several supergroups, none of which is included in the kingdom Fungi.
Slime molds can generally be divided into two main groups.
A plasmodial slime mold is enclosed within a single membrane without walls and is one large cell. This "supercell" (a syncytium) is essentially a bag of cytoplasm containing thousands of individual nuclei. See heterokaryosis.
By contrast, cellular slime molds spend most of their lives as individual unicellular protists, but when a chemical signal is secreted, they assemble into a cluster that acts as one organism.
Modern classification
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Myxogastria or myxomycetes: syncytial, plasmodial, or acellular slime molds
Dictyosteliida or dictyostelids: cellular slime molds
Protosteloids: amoeboid slime-molds that form fruiting bodies
Even at this level of classification there are conflicts to be resolved. Recent molecular evidence shows that, while the first two groups are likely to be monophyletic, the protosteloids are likely to be polyphyletic. For this reason, scientists are currently trying to understand the relationships among these three groups.
Slime mold Trichia varia
The most commonly encountered are the Myxogastria. A common slime mold that forms tiny brown tufts on rotting logs is Stemonitis. Another form, which lives in rotting logs and is often used in research, is Physarum polycephalum. In logs, it has the appearance of a slimy web-work of yellow threads, up to a few feet in size. Fuligo forms yellow crusts in mulch.
Plasmodia
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In Myxogastria, the plasmodial portion of the life cycle only occurs after syngamy, which is the fusion of cytoplasm and nuclei of myxoamoebae or swarm cells. The diploid zygote becomes a multinucleated plasmodium through multiple nuclear divisions without further cell division. Myxomycete plasmodia are multinucleate masses of protoplasm that move by cytoplasmic streaming. In order for the plasmodium to move, cytoplasm must be diverted towards the leading edge from the lagging end. This process results in the plasmodium advancing in fan-like fronts. As it moves, plasmodium also gains nutrients through the phagocytosis of bacteria and small pieces of organic matter.
The plasmodium also has the ability to subdivide and establish separate plasmodia. Conversely, separate plasmodia that are genetically similar and compatible can fuse together to create a larger plasmodium.
