The new mathematical method determines the "selective signature" of a gene -- the pattern of fast or slow evolution of that gene across a group of species -- and then uses the signature to infer gene function or to map changes to ecological shifts.

By reversing the usual order of inquiry -- studying an organism, then trying to identify which genes are involved in a particular function -- the Massachusetts Institute of Technology scientists said they hope to hasten the understanding of microbial evolution by taking advantage of the nearly 2,500 microbes already sequenced.

"By comparing across species, we looked for changes in genes that reflect natural selection and then asked 'How does this gene relate to the ecology of the species it occurs in?' " said Assistant Professor Eric Alm, who led the research. "The selective signature method also allows us to focus on a single species and better understand the selective pressures on it."

The study that included graduate student B. Jesse Shapiro appeared in the February issue of PLoS Genetics.