Bacteria and Viruses Engage in Deep Sea Thermal Warfare

Deep at the bottom of the ocean, a microbial war is being waged between viruses and bacteria clustered around hydrothermal vents spewing mineral-rich water.

The viruses, like loot-hungry pirates, highjack the bacteria, which store clusters of elemental sulfur within them. Then, instead of making off with the sulfur goods, the viruses force the bacteria to burn off their sulfur reserves, using the energy released in the process to replicate.

By doing so, these deep sea viruses are accessing vast energy reserves in the form of elemental sulfur, according to Gregory Dick, a marine microbiologist at University of Michigan.

Dick and his collaborators published their findings in the journal Science Express. They collected their samples from hydrothermal vents in the western Pacific Ocean and the Gulf of California at depths greater than 6,000 feet. The vents spew mineral-rich seawater heated to more than 500 degrees Fahrenheit.

"We suspect that these viruses are essentially hijacking bacterial cells and getting them to consume elemental sulfur so the viruses can propagate themselves," said lead study author Karthik Anantharaman, also from the University of Michigan.

The study offers the first evidence of relationship of microbial organisms living in what's called a "chemosynthetic system," meaning they rely on solely on inorganic compounds, rather than sunlight, as their energy source.

"Viruses play a cardinal role in biogeochemical processes in ocean shallows," said National Science Foundation (NSF) ocean science program Director David Garrison. "They may have similar importance in deep-sea thermal vent environments."

The results of the study suggest that viruses play an important role in thriving ecosystems.

"The results hint that the viruses act as agents of evolution in these chemosynthetic systems by exchanging genes with the bacteria," Dick said in a statement from the NSF. "They may serve as a reservoir of genetic diversity that helps shape bacterial evolution."

The bacteria detailed in the study were a common type known as SUP05, which are known to consume sulfur. The viruses, on the other hand, included five previously unknown species.

That the bacteria subsist on sulfur is intriguing because as levels of oxygen in oceans decrease, it could be a way for the organisms to survive.

"SUP05 bacteria, which are known to generate the greenhouse gas nitrous oxide, will likely expand their range as oxygen-starved zones continue to grow in the oceans," the NSF said in a statement.

The viruses deep beneath the sea enhance bacterial consumption of the elemental sulfur, but to the benefit of the viruses themselves, the researchers said.

"There seems to have been an exchange of genes, which implicates the viruses as an agent of evolution," Dick said.