More than a mile beneath the ocean's surface, as dark clouds of mineral-rich water billow from seafloor hot springs called hydrothermal vents, unseen armies of viruses and bacteria wage war.
Like pirates boarding a treasure-laden ship, the viruses infect bacterial cells to get the loot: tiny globules of elemental sulfur stored inside the bacterial cells.
Instead of absconding with their prize, the viruses force the bacteria to burn their valuable sulfur reserves, then use the unleashed energy to replicate.
"Our findings suggest that viruses in the dark oceans indirectly access vast energy sources in the form of elemental sulfur," said University of Michigan marine microbiologist and oceanographer Gregory Dick, whose team collected DNA from deep-sea microbes in seawater samples from hydrothermal vents in the Western Pacific Ocean and the Gulf of California.
"We suspect that these viruses are essentially hijacking bacterial cells and getting them to consume elemental sulfur so the viruses can propagate themselves," said Karthik Anantharaman of the University of Michigan, first author of a paper on the findings published this week in the journal Science Express.
Similar microbial interactions have been observed in shallow ocean waters between photosynthetic bacteria and the viruses that prey upon them. But this is the first time such a relationship has been seen in a chemosynthetic system, one in which the microbes rely solely on inorganic compounds, rather than sunlight, as their energy source.
"Viruses play a cardinal role in biogeochemical processes in ocean shallows," said David Garrison, a program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research. "They may have similar importance in deep-sea thermal vent environments."
The results suggest that viruses are an important component of the thriving ecosystems--which include exotic six-foot tube worms--huddled around the vents.
"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."