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Your Cheatin' Germs

Cheating isn't limited to kids in classrooms: Duplicitous behavior is common in many social animals, from ants to lions. Now a team of microbiologists says that cheating could even take place among the lowliest of social slime.

The microbe Myxococcus xanthus lives in soil around the world. Unlike most bacteria, this one lives in colonies that ooze around in small slimy clumps, hunting other microorganisms. When food gets scarce, the colony builds tiny fruiting bodies. Inside, some of the group members turn into spores that can recolonize when times aren't so tough. Other group members sacrifice themselves, and some scientists think they feed the bacteria that became spores with their disintegrated bodies.

This kind of life cycle is ripe for microbial misbehavior, says Gregory Velicer of Michigan State University in East Lansing. He realized that strains of the bacterium that never self-destruct could take advantage of their peers that do offer themselves up when the colony makes fruiting bodies. To test this idea, Velicer used a lab-bred strain that had lost the ability to form fruiting bodies. When mixed with a colony of regular Myxococcus, the defective strains behaved as blatant cheaters, the researchers report in the 6 April issue of Nature. They didn't contribute any nutrients to the fruiting bodies, yet they formed 50 times more spores--thereby preserving their genes--than the other bacteria did.

It's an intriguing concept, muses evolutionary biologist Joan Strassmann of Rice University in Houston, Texas, but she says it's an open question whether this cheating will be common in nature, in part because cheaters might not easily find their way into other colonies. But Velicer points out that the clumps of spores are sticky, so the spores of devious bacteria could easily glom onto another strain and take advantage of it.