ScienceShot: Amoeba 'Farmer' Uses Organic Pesticide

The world’s smallest farmer also uses pesticides. That’s the conclusion of a new study on Dictyostelium discoideum, or “Dicty,” an amoeba with an unusual life cycle. Dicty spends most of its life as a single cell, but when food resources get tight, the cells clump together and transform into a sluglike creature half a centimeter long that heads for greener pastures; there it morphs into a so-called fruiting body with a long stalk and a spore-filled head (pictured). It also takes bacteria with it, which it harvests like crops after they burst out with the spores. Now, reporting online today in the Proceedings of the National Academy of Sciences, researchers have found that Dicty carries a second set of bacteria, which are not food but produce pyrrolnitrin, a chemical that kills other bacteria and fungi. Surprisingly, pyrrolnitrin doesn’t destroy Dicty’s “crops,” but it does keep competing bacteria away, functioning a bit like an organic pesticide. The successful harvest allows Dicty to live as single cells until the food runs out once again.