Suicidal Algae Help Their Relatives and Harm Their Rivals
Pierre Durand, an evolutionary biologist at the University of the Witwatersrand in Johannesburg, has been trying to figure out why. In an earlier study with a single-celled algae called Chlamydomonas reinhardtii, Durand grew cells in the liquid where other cells had previous killed themselves (in response to heat stress). The algae grew faster than usual in the suicide liquid. But liquid where cells had been killed from the outside (the researchers tore them apart with sound waves) was harmful to living cells. A cell that dies suddenly leaks toxic contents into its surroundings, but cells that commit suicide apparently don’t—and even leave behind something healthy for other cells to eat.
Cells that have killed themselves on purpose leave a clear biochemical signature, Durand says. They cut up their DNA in an orderly way, for example, and alter their outer membranes. In a new study, he and his coauthors again stressed out Chlamydomonas reinhardtii cells by heating them. Once more, they looked for the signs of cellular suicide. Then they removed some of the liquid in which the algae had killed themselves. For comparison, they’d also removed some liquid before the cells died. They fed both liquids to new batches of C. reinhardtii cells, as well as two other species of Chlamydomonas.
As before, the cells growing in suicide liquid grew more quickly than controls. But more surprisingly, the two other algae species fared much worse in this liquid. After a few days, their growth tanked, compared to cells grown in pre-suicide liquid.
