Spiteful bacteria. Two words you probably haven’t heard together. Then again, you probably haven’t heard of altruistic bacteria either, but both sorts of microbes are out there–and in many cases in you.

Bacteria lead marvelously complicated social lives. As a group of University of Edinburgh biologists reported today in Nature, a nasty bug called Pseudomonas aeruginosa, which causes lung infections, dedicates a lot of energy to helping its fellow P. aeruginosa. The microbes need iron, which is hard for them to find in a usable form in our bodies. To overcome the shortage, P. aeruginosa can release special molecules called siderophores that snatch up iron compounds and make them palatable to the microbe. It takes a lot of energy