Physarum polycephalum

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Physarum polycephalum belongs to phylum Amoebozoa, infraphylum Mycetozoa, and class Myxogastrea. P. polycephalum, often referred to as the “many-headed slime,” is a slime mold that inhabits shady, cool, moist areas, such as decaying leaves and logs.

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[edit] Characteristics

This protist may be seen without a microscope; P. polycephalum is typically yellow in color, and eats fungal spores, bacteria, and other microbes. P. polycephalum is one of the easiest eukaryotic microbes to grow in culture, and has been used as a model organism for many studies involving amoeboid movement and cell motility.

[edit] Life cycle

The main vegetative phase of P. polycephalum is the plasmodium (the active, streaming form of slime molds). The plasmodium consists of networks of protoplasmic veins, and many nuclei. It is during this stage that the organism searches for food. The plasmodium surrounds its food and secretes enzymes to digest it.

If environmental conditions cause the plasmodium to desiccate during feeding or migration, Physarum will form a sclerotium. The sclerotium is basically hardened multinucleated tissue that serves as a dormant stage, protecting Physarum for long periods of time. Once favorable conditions resume, the plasmodium reappears to continue its quest for food.

As the food supply runs out, the plasmodium stops feeding and begins its reproductive phase. Stalks of sporangia form from the plasmodium; it is within these structures that meiosis occurs and spores are formed. Sporangia are usually formed in the open so that the spores they release will be spread by wind currents.

Spores can remain dormant for years if need be. However, when environmental conditions are favorable for growth, the spores germinate and release either flagellated or amoeboid swarm cells (motile stage); the swarm cells then fuse together to form a new plasmodium.

[edit] Streaming behavior

The movement of P. polycephalum is termed shuttle streaming. Shuttle streaming is characterized by the rhythmic back-and-forth flow of the protoplasm; the time interval is approximately two minutes. The forces of the streaming vary for each type of microplasmodium.

The force in amoeboid microplasmodia is generated by contraction and relaxation of a membranous layer probably consisting of actin (type of filament associated with contraction). The filament layer creates a pressure gradient, over which the protoplasm flows within limits of the cell periphery.

The force behind streaming in the dumbbell-shaped microplasmodia is generated by volume changes in both the periphery of the cell and in the invagination system of the cell membrane.

[edit] Care

Physarum Polycephalum can be easily cultivated in the lab for research purposes and there are many resources available online for ordering cultures. The most simple way of cultivating P. polycephalum is to grow it in its plasmodial stage on an agar or filter paper medium. Keep the culture out of direct light and "rinse" it lightly weekly to ensure growth. Once your culture begins to grow you will need to feed it. In the wild, P. polycephalum will usually eat bacteria and dead organic matter. However, in the lab you will need to feed your culture daily with old fashioned oats. It is important to note that instant oats will kill the P. polycephalum and should not be used. As your culture grows you may wish to transfer it to multiple petri dishes. Simply remove a portion of the active plasmodium and place it gently on your agar, or filter paper culture medium. If you wish to induce sporangia formation, expose the plasmodium stage P. polycephalum to small increments of sunlight each day until sporangia form.

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