Viruses rule the deep sea

Posted by Alla Katsnelson
[Entry posted at 27th August 2008 06:00 PM GMT]

Viruses in the deepest ocean environments are unexpectedly strong regulators of the deep sea biosphere, according to a paper published tomorrow (August 28) in Nature. By infecting and killing bacteria and other prokaryotes viruses are the main producers of the organic matter that sustains life at 1000 meters deep and below. By generating this biomass, viruses also make major contributions to the carbon cycle and other geochemical processes. "This shows that a very large amount of the carbon that reaches the sea floor is going through pathways that were commonly thought to be relatively minor," said Jed Fuhrman, an ocean biologist at the University of Southern California who was not involved in the study. "The whole idea that viruses have any significance in marine systems is only 15 to 20 years old." Approximately 65% of the Earth is dominated by deep sea, or benthic, ecosystems. The sea floor is one of the hardest environments for research, Fuhrman explained, because of the distances and logistical challenges involved in conducting experiments. The researchers, led by Roberto Danovaro of the Polytechnic University of Marche, Italy, collected 232 samples of sediment from the deep sea. They found that viruses were surprisingly abundant in their samples, and that they were reproducing locally, rather than migrating down from surface waters. The deeper the water, the more virus-induced death they observed in the bacteria, with viral infection responsible for about 80% of bacterial death in the deep sea samples. "The viruses are the key agents of mortality in bacteria," said Antonio Dell'Anno of the Polytechnic University of Marche, Italy, an author on the study. "The result is a huge amount of organic material released by killing these cells," which in turn "represents new food for other cells that have not been infected by viruses," he said. It's also a carbon source that acts as "a sort of shunt," he explained, regulating the metabolism of the deep sea. Virus-induced bacterial death, the researchers estimate, produces as much as 0.37 to 0.63 gigatonnes of carbon each year. The fact that the turnover of biomass is so dynamic came as a surprise to researchers, he said. "Previously, people hadn't thought about viruses when they did their benthic modeling," said Fuhrman, adding that the study's strength lies in the fact that the researchers collected data from many deep ocean locations. The discovery that there's such a high degree of carbon production in deep sea environments means that researchers will now have to adapt their models of ocean functioning and how it contributes to the overall carbon cycle, both he and Dell'Anno noted.