"The results hint that the viruses act as agents of evolution in these chemosynthetic systems by exchanging genes with the bacteria," Dick said. "They may serve as a reservoir of genetic diversity that helps shape bacterial evolution."
The scientists collected water samples from the Eastern Lau Spreading Center in the Western Pacific Ocean and the Guaymas Basin in the Gulf of California.
The samples were taken at depths of more than 6,000 feet, near hydrothermal vents spewing mineral-rich seawater at temperatures surpassing 500 degrees Fahrenheit.
Back in the laboratory, the researchers reconstructed near-complete viral and bacterial genomes from DNA snippets retrieved at six hydrothermal vent plumes.
In addition to the common sulfur-consuming bacterium SUP05, they found genes from five previously unknown viruses.
The genetic data suggest that the viruses prey on SUP05. That's not too surprising, said Dick, since viruses are the most abundant biological entities in the oceans and are a pervasive cause of mortality among marine microorganisms.
The real surprise, he said, is that the viral DNA contains genes closely related to SUP05 genes used to extract energy from sulfur compounds.
When combined with results from previous studies, the finding suggests that the viruses force SUP05 bacteria to use viral SUP05-like genes to help process stored globules of elemental sulfur.
The SUP05-like viral genes are called auxiliary metabolic genes.
"We hypothesize that the viruses enhance bacterial consumption of this elemental sulfur, to the benefit of the viruses," said paper co-author Melissa Duhaime of the University of Michigan. The revved-up metabolic reactions may release energy that the viruses then use to replicate and spread.
How did SUP05-like genes end up in these viruses? The researchers can't say for sure, but th
|Contact: Cheryl Dybas|
National Science Foundation