There’s been an unexpected development in our understanding of drug resistance in bacteria. The accepted scenario was a simple case of evolutionary selection. In a bacterial population exposed to a killer drug, a few lucky individuals might have a genetic mutation that kept them alive. They survived to reproduce, while the rest of the population perished. In short order, the entire colony consisted only of the offspring of the drug-resistant founders.

But a new study finds that just a few resistant mutants can protect large numbers of normal bacteria that would have been thought to be susceptible to the drug therapy. The research appears in the journal Nature. [Henry Lee et al, http://bit.ly/9NG5Ud]

The key seems to be that the drug-resistant mutants produce large amounts of compounds called indoles, which help bacteria tough out tough times. And the indoles from the mutants buck up the regular, nonresistant bacteria. The mutants themselves seem to be acting altruistically—their own growth is slowed by their indole production.

The finding should lead to new strategies to fight drug resistance. And it could also improve our take on evolutionary dynamics, in systems that apparently experience selection pressure at both the individual and group levels.