"We found that the differentiation between populations was restricted to a few small patches in the genome," says Eric Alm, the Karl Van Tassel (1925) Career Development Associate Professor of Civil and Environmental Engineering and Biological Engineering and an associate member of the Broad Institute.
Professor Martin Polz of CEE, co-principal investigator on the project, adds, "Similar patterns have been observed in animals, but we didn't expect to see it in bacteria"
The process of ecological differentiation in bacteria, the researchers found, is similar to that in malaria-transmitting mosquitoes: Some populations develop resistance to antimalarial agents by means of a single gene sweep, while other populations sharing the same habitat do not. The stickleback fish has also been shown to follow this pattern of "sympatric speciation" in shared habitats.
"Even though the sources of genetic diversity are quite different between bacteria and sexual eukaryotes, the process by which adaptive diversity spreads and triggers ecological differentiation seems very similar," says first author Jesse Shapiro PhD '10, a postdoc at Harvard University who did his graduate work in Alm's lab at MIT.
The researchers performed the work using 20 complete genomes of the bacterium Vibrio cyclitrophicus that had recently diverged into two ecological populations adapted to microhabitats containing different types of zooplankton, phytoplankton, and suspended organic particles in seawater. In a previous study based on just a few marker genes, they had predicted that these closely related Vibrio populations were in the process of developing into two distinct habitat-associated populations.
|Contact: Denise Brehm|
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering