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  Plasmodial Slime Molds

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The true plasmodial slime molds exist in nature as a plasmodium, a multinucleate blob of protoplasm up to several centimeters in diameter, without cell walls and only a cell membrane to keep everything in. This “supercell” (a syncytium) is essentially a large ameba with thousands of individual nuclei that feeds by engulfing its food (mostly bacteria) with pseudopodia in a process called phagocytosis. Thus the slime mold ingests its food and then digests it. 

 

When the plasmodium runs out of food, or environmental conditions become harsh, they often form elaborate (often beautiful) fruiting bodies made mostly from calcium carbonate and protein that produce spores that allow them to move to a new food source. These later germinate to form uninucleate amebas or flagellated swarm cells. These later fuse and then divide mitotically to form a plasmodium, completing the life cycle. One fascinating thing about plasmodial slime molds is that the millions of nuclei in a single plasmodium all divide at the same time. This makes slime molds ideal tools for scientists studying mitosis, the process of nuclear division.

 

Occasionally, during rainy periods, large plasmodia (up to a few meters in diameter) crawl out of the woods and into people's lawns and gardens. The plasmodium may be ugly to some, but it is not harmful. Slime molds cause very little damage. The plasmodium ingests bacteria, fungal spores, and maybe other smaller protozoa. Their ingestion of food is one reason slime molds are not considered to be fungi. Fungi produce enzymes exogenously (outside of their bodies) that break down organic matter into chemicals that are absorbed through their cell walls, not ingested.

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