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.