Research Challenges Theory that Microbes Follow Different Evolutionary Rules as Higher Organisms
by Sarah Yang
Berkeley - A new study led by researchers at the University of California, Berkeley, has found genetic differences in a sampling of a species of hot spring-loving microbes from around the world.
The findings, published online today (Thursday, July 24) by the journal Science, at the Science Express website, challenges the prevailing theory of microbial biodiversity.
It is well accepted in evolutionary science that species of animals and plants are more closely related when they are geographically near each other. When it comes to the tiny world of microbes, however, most scientists believe that different evolutionary rules apply.
"The current dogma has been that, for microbes, what determines diversity is not geographic distance but specific environments," said John Taylor, professor of plant and microbial biology at UC Berkeley's College of Natural Resources and the head of the lab where the study was conducted. "The motto for microbes has been, 'Everything is everywhere, but the environment selects.' "
To test this theory, Rachel Whitaker, a UC Berkeley graduate student in Taylor's lab and lead author of the paper, trekked around the globe - by helicopter in some remote areas - to collect samples of a microbe called Sulfolobus islandicus, which thrives in the extreme environments of geothermal hot springs and volcanic vents. Sulfolobus microbes belong to the domain archaea - discovered in the 1970s - and can withstand highly acidic conditions and temperatures as high as 180 degrees Fahrenheit.
The samples were collected from the Mutnovsky Volcano and the Uzon Caldera-Geyser Valley region on the Kamchatka Peninsula in eastern Russia, the Lassen Volcanic and Yellowstone national parks in North America, and the volcanic region of western Iceland.
The researchers' analysis also includes a large portion of previously collected Sulfolobus samples that were provided by co-author Dennis Grogan, associate professor of biological sciences at the University of Cincinnati.
In all, the researchers analyzed the DNA of 78 separate cultures of Sulfolobus islandicus and found small but significant levels of genetic differentiation between populations that live in different areas, despite the fact that they existed in similar ecological conditions.
"It makes sense that thermophiles cannot migrate over long distances since they are specifically adapted to life in the extremely hot acidic environments of a geothermal hot spring," said Whitaker. "It's not too surprising that geographically isolated populations are evolving independently. This is predicted by population genetic theory but has never before been shown in microbial species."
Moreover, the study shows that genetic differences increased in direct correlation with geographic distance.
"If this type of geographic pattern occurs in other microbes, it means the microbial world is even more diverse than we had previously predicted, which is astounding," said Whitaker.
Taylor said the study has implications for how researchers view and treat microbes that emerge in different parts of the world.
"Many bacteria and fungi cause disease, and genetically different species may exhibit different behavior," said Taylor. "To treat diseases, researchers need to understand exactly which species they're working with."
Scientists working on a pathogen that emerged in China, for example, cannot automatically assume that the same species of pathogen that emerged in the United States will behave the same way, the researchers said.
NASA provided funding for Whitaker's graduate studies. The National Institutes of Health and the National Science Foundation also provided support for the study.