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 the valuable sulfur reserves, then use the unleashed energy to replicate, eventually filling the bacterial cells to the bursting point.
"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 J. Dick, whose team collected DNA from deep-sea microbes in seawater samples from hydrothermal vent sites in the western Pacific Ocean and the Gulf of California.
The study identifies viruses as key players in the thriving ecosystems – which include exotic 6-foot tube worms, giant clams and mussels, as well as shrimp – huddled around deep-sea hydrothermal vents.
In addition, they hint that the viruses act as agents of evolution in chemosynthetic systems by swapping genes with the bacteria, Dick said. "We suggest that the viruses serve as a reservoir of genetic diversity that helps shape bacterial evolution," he said.
A paper summarizing the findings is scheduled for online publication May 1 in Science. The first author is Karthik Anantharaman, a doctoral student in Dick's lab at the Department of Earth and Environmental Sciences.
"We hypothesize that the viruses enhance bacterial consumption of this elemental sulfur, to the benefit of the viruses," said co-author Melissa Duhaime, an assistant research scientist in the U-M Department of Ecology and Evolutionary Biology. The revved-up metabolic reactions may release energy that the viruses then use to replicate and spread.
Similar microbial interactions have been observed in shallow ocean waters between photosynthetic bacteria and the viruses that prey on 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 sunshine, as their energy source.