In the final frenzy of reproduction and death, social amoebas secrete proteins that help preserve a starter kit of food for its offspring.
Dictyostelium discoideum, a type of slime mold in soil, eats bacteria. Some wild forms of this species essentially farm the microbes, passing them along in spore cases that give the next generation of amoebas the beginnings of a fine local patch of prey.
Lectins create a different way for the amoebas to treat bacteria: as actual symbionts inside cells, instead of as prey or infections, says study coauthor Adam Kuspa, a molecular cell biologist at Baylor College of Medicine in Houston. In a lab test of this ability, coating other bacteria with lectin derived from a plant allowed bacteria to slip inside cells from mice and survive as symbiotic residents.
The findings mark another chapter in a story that has been upending decades of what people thought they knew about social amoebas eating bacteria. The basic, almost alien, scenario is still true: D. discoideum amoebas, nicknamed Dicty, start life as single cells. When food dwindles, cells come together into a much bigger, multicellular slug-shaped creature with eight to 10 types of cells and the power to crawl. It then develops into something more like a fungus with a stalk holding up a case of spores, which start the next generation of amoebas.