The Black Queen Hypothesis: Basis of a new evolutionary theory

Microorganisms can sometimes lose the ability to perform a function that appears to be necessary for their survival, and yet they still somehow manage to endure and multiply. How can this be? The authors of an opinion piece appearing in mBio®, the online open-access journal of the American Society for Microbiology, on March 27 explain their ideas about the matter. They say microbes that shed necessary functions are getting others to do the hard work for them, an adaptation that can encourage microorganisms to live in cooperative communities.

The Black Queen Hypothesis, as they call it, puts forth the idea that some of the needs of microorganisms can be met by other organisms, enabling microbes that rely on one another to live more efficiently by paring down the genes they have to carry around. In these cases, it would make evolutionary sense for a microbe to lose a burdensome gene for a function it doesn't have to perform for itself. The authors, Richard Lenski and J. Jeffrey Morris of Michigan State University, and Erik Zinser of the University of Tennessee, named the hypothesis for the queen of spades in the game Hearts, in which the usual strategy is to avoid taking this card.