Photo: Kim Fleming (flickr)
Our last program was about an amazing slime mold, called Dictyostelium discoideum, that eats bacteria on rotting logs.
When bacterial food runs low, tens of thousands of formerly individual amoeba-like Dictyostelium cells come together and pile up into a little mound a couple of millimeters high.
The mound tips over and assumes a shape something like a tiny slug.
Slug-Like Creature, Grex
This slug-like creature, called a grex, crawls to a new location, then plants its front end in the log, raises the rest of its body into the air, and releases spores that become individual amoeba-like single-celled bacteria eaters again.
This amazing slime mold raises a big question: how do those amoeba-like cells get organized into the slug-like form?
How Do They Organize?
Experiments beginning in the late 1940′s have revealed part of the answer. When Dictyostelium cells get hungry, they begin to release a chemical called cyclic AMP into their environment. The first few cells to release the chemical become so-called founder cells, or leaders in the organizational process.
When another Dictyostelium cell detects cyclic AMP, it does two things: first, it moves toward the source of the chemical; second, it releases a little of the chemical on its own.
When tens of thousands of slime mold cells behave this way, the result is waves of the chemical cyclic AMP going away from those cells that began releasing it first, and streams of slime mold cells moving toward those founder cells.
So cells of the slime mold Dictyostelium get organized into a shape by working like a bucket brigade, relaying a chemical message from one cell to surrounding cells.
Biologists suspect that the shapes of other living things, from trees to humans, may also be partly controlled by chemical communication between cells.