What is your favorite bacterium

Amoebas as small farmers

The amoeba of the species Dictyostelium discoideum are mobile unicellular organisms. Its diameter is just 20 micrometers, the fiftieth part of a millimeter. Although they are significantly larger than bacteria, they can only be seen under a microscope or under a very good magnifying glass. When the unicellular organisms combine, however, they form an organism that is visible to the naked eye: a kind of slime mold, explains biologist Debra Brock from Rice University in Houston, Texas.

"The species lives in two different forms. On the one hand, it is a unicellular amoeba that feeds on bacteria. But when food is scarce, the unicellular amoeba becomes a multicellular organism."

Tens of thousands of amoebas combine to form a slime mold, which forms fruiting bodies and spores, from which unicellular amoebas are formed. You knew that. What was unknown, however, was that Dictyostelium discoideum Literally grows bacteria.

"Some amoebas are able to spread the bacteria. They don't just eat them, they harvest the bacteria and, if necessary, sow them elsewhere. The amoebas take them to places where bacteria have not yet grown. We look at those Amoebas therefore as simple farmers. "

Only a third of the amoebas are such small farmers. They form a kind of reserve from their favorite bacteria. And in times of need they don't just eat them, but sow them in order to reap a great harvest later. The non-farmers among the amoebas, on the other hand, live as bacteria hunters and gatherers. With good living conditions, you have an advantage. Because they eat more bacteria than the agriculturally active amoebas. In times of hunger, however, the farmers' hour strikes because they have taken precautions, explains biologist Debra Brock.

"The kind Dictyostelium discoideum generally prefers a certain group of bacteria: the gram-negative. Other bacteria, the gram-positive ones, don't like them that much. But basically they sow and reap different species. Most of these bacteria are used as food by the amoeba. We suspect that some bacteria may also help them defend themselves. Because they produce chemicals that keep other organisms away from the amoeba's food sources. "

What brought the amoeba to agriculture was probably their social way of life. They can survive individually or, in difficult times, form a community as a slime mold. In this way, societies emerge from individuals, similar to ants or humans. Possibly all organisms that organize as communities tend towards agriculture.