February 22, 2012
Microbes Found Speciating In Russian Hot Spring
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It was Darwin who, upon studying evolving creatures, wondered how species diverge if they are living together. “That question really hasn´t been answered very well, even in the macro-organisms that we´ve studied for hundreds of years,” University of Illinois microbiology professor Rachel Whitaker ponders.
This is an example of what researchers call sympatric speciation in a microorganism, or one lineage diverging into two or more species with no physical or mechanical barriers keeping them separated.
“Bacteria, and their distantly-related microbial cousins the archaea, are even more difficult to study because they have so many different ways of sharing genetic information,” Whitaker continued. Even with new sequencing technologies, the task of studying microbial evolution is daunting.
Whitaker and her team focused on a heat-loving species of the bacteria-like archaea, Sulfolobus islandicus, because it is one of few microorganisms that live in distinct “island” populations created by geothermal hot springs.
The researchers sequenced the genomes of twelve strains of S. islandicus from a hot spring in the Mutnovsky Volcano region of Kamchatka. By comparing sequences at multiple sites on the microbes´ single (circular) chromosome, the researchers were able to reconstruct the genetic history of each of the strains.
Two distinct groups of S. islandicus were found among the twelve strains. The microbes were swapping genes with members of their own group more than expected, but sharing genes with the other group less than expected. Additionally the exchange of genetic material between the two groups was found to be decreasing over time.
This indicates that the two groups are already separate species, even though they share the same habitat, Whitaker explained. The differences between the two groups were slight, but speciation was clearly underway, she said.
Researchers saw a mosaic of differences along the chromosome, with vast “continents” of variation and smaller “islands” of stability, the closer they peered at the patterns of change. Those islands likely represent regions that are under selective pressure, Whitaker said; something in their environment is weeding out the microbes that don´t have those genes or sets of genes. The variable regions are more fluid, with genes coming and going (a process called recombination) and mutations increasing diversity.
The findings provide the first evidence that sympatric speciation occurs in a microbe.
“We caught them speciating,” she said. “They do exchange some genes — just not very many. So now we know you don´t have to have a (geographic or mechanical) barrier to recombination for speciation to occur. All you have to have is selection pulling the two groups apart, which nobody knew before.”
This study provides a glimpse of the profound genetic diversity that likely occurs everywhere in wild microbial populations, researchers concluded. “What we see as two different species are 0.35 percent different across the chromosome; that´s about one-third of the distance between human and chimp,” she said.
The two distinct groups of microbes are “orders of magnitude” more similar to each other than groups normally considered separate species. “That means there are orders of magnitude more species of microbes than we ever thought there were and that´s kind of mind-boggling.”
The study appears in the journal PLoS Biology. The research team included scientists from Arizona State University, the University of California at Davis, and the University of Oxford.
Image Caption: The research was conducted on microbes found in a single geothermal hot spring in the Mutnovsky Volcano region of Kamchatka, Russia. | Photo by Rachel Whitaker
On the Net:
- University of Illinois
- PLoS Biology
- Arizona State University
- University of California at Davis
- University of Oxford