Worlds within worlds: evolution of the vertebrate gut microbiota.

Ley, Gordon and colleagues have analysed and compared published sequences of bacterial communities from humans with both free-living communities and those that are associated with diverse animals. They conclude that gut-associated microbiotas are profoundly different from other free-living microbiotas, and call for widespread sampling of the human gut microbiota to study how different cultures, lifestyles and technologies are impacting on the biodiversity within these fascinating communities.