Many positive aspects of modern human society are the fruit of millennia of cooperative interactions between members of our species. Yet the evolutionary origins of cooperative behaviour in social animals and insects remains one of the most intriguing puzzles in biology. Cooperation is of evolutionary importance because it provides benefits to participants that are unavailable to isolated individuals. Starting with non-social ancestors of the soil bacterium Myxococcus xanthus, Gregory J. Velicer and Yuen-tsu N. Yu of the Max Planck Institute for Developmental Biology in Tbingen observed the real-time evolution of novel forms of cooperative behaviour between bacterial cells in the laboratory. As reported in a study appearing in the 4 September issue of Nature, the bacteria evolved the ability to cooperatively swarm across laboratory surfaces.

In addition to social animals and insects, many species of bacteria are now also known to engage in various cooperative behaviours such as the production of quorum sensing compounds and adhesive polymers that allow the formation of biofilms. Even more strikingly, the myxobacteria (to which M. xanthus belongs) are a group of particularly social bacteria. Large groups of these cells cooperate to swarm across solid surfaces in search of prey organisms which they hunt and kill together like a wolf pack. Moreover, when they encounter starvation conditions, groups of up to 100,000 individuals M. xanthus cells aggregate together to construct three-dimensional fruiting structures in which stress-resistant spores are formed.

Wild-type M. xanthus normally moves cooperatively by a mechanism known as S-motility that involves contact between cells mediated by filamentous appendages on the cell surface known as pili. Although cells can also move individualistically by means of an alternative motility me
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Contact: Dr. Gregory Velicer
gregory.velicer@tuebingen.mpg.de
Max-Planck-Gesellschaft
5-Sep-2003