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How A Microscopic Organism Changes From An Amoeba To A Grex

Here is the strange life story of a nearly microscopic organism that eats bacteria in rotting logs and damp earth.

green amoeba sticker

Photo: Wolfram Burner (flickr)

Amoebas combine to form a grex.

Here is the strange life story of a nearly microscopic organism that eats bacteria in rotting logs and damp earth. The technical name for the organism is Dictyostelium discoideum.

Amoeba-Like Organism

When this organism is in the bacteria-eating stage of its life, it takes the form of amoeba-like single-celled organisms with a certain limited ability to move. At this stage, Dictyostelium is pretty much like other single-celled organisms feeding on bacteria.

Things get interesting when these amoeba-like organisms exhaust the food supply in their vicinity. Then, tens of thousands of them join to form moving streams that converge toward a central point.

They pile up into a little mound that grows taller and taller until it reaches a height of a couple of millimeters or so. Then the mound tips over and assumes a shape something like a tiny slime-covered slug, about three millimeters long.

Technically, this newly-organized aggregation of cells is called a grex.

Creating A Grex

The tiny grex crawls to a new location, always keeping its front tip slightly raised.

When the grex arrives at a new spot with a better supply of bacterial food, it plants its front tip onto a nearby surface, forming a stalk, and raises its body into the air. The cells in the body then become spores, which come loose and disperse.

Each spore becomes an amoeba-like individual, foraging for bacteria. That brings us back to where we started in the amazing life cycle of the slime mold Dictyostelium discoideum.

This slime mold is not only amazing but thought-provoking. How do those tens of thousands of amoeba-like cells cooperate to form that slug-like grex? Next time: a piece of the answer.

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