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Hijack! Viruses plunder sulphur from deep-sea bacteria at hydrothermal vents
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In deep sea waters, over a mile below the surface, microbes rely on inorganic compounds such as sulphur as an energy source rather than sunshine. There, in the mineral-rich waters that cascade from hypothermal vents (seafloor hot springs) viruses prey on the SUP05 bacterium to plunder the energy released from its sulphur reserves. SUP05 is the gene that is responsible for energy extraction from sulphur. This relationship between the bacteria and the virus has featured exchange of genes as the viral DNA contains genes closely related to the bacterial SUP05 genes. This has important implications for implicating viruses as agents of evolution as the viruses then force the SUP05 bacteria to use viral SUP05-like genes to process elemental sulphur. These are the findings of a paper published online in the journal Science on May 1st from researchers in the University of Michigan.

Microbial interactions like these have been previously observed in shallow to mid-depth ocean waters featuring photosynthetic bacteria. The current study used an unmanned submarine at a depth of over 6,000 feet, to obtain DNA samples from deep-sea microbes at hydrothermal vent sites. These samples were collected on trips to the Eastern Lau Spreading Centre in the Western Pacific and the Guaymas Basin in the Gulf of California.

Having obtained the samples, the research team set about reconstructing the viral and bacterial genomes by combining information from DNA snippets retrieved at six sites. As well as confirming the presence of the common sulphur-consuming bacterium SUP05, they discovered genes from five viruses that had never been previously identified. The most surprising result was that the viral DNA contained genes closely related to the bacterial SUP05 genes that are responsible for energy extraction from sulphur.

Co-author on the study, Dr Melissa Duhaime explains the viral strategy: "We hypothesize that the viruses enhance bacterial consumption of this elemental sulphur, to the benefit of the viruses.” First author Karthik Anantharaman continues: “We suspect that these viruses are essentially hijacking bacterial cells and getting them to consume elemental sulphur so the viruses can propagate themselves." It is not known for sure how the SUP05-like genes ended up in the viruses. However, the researchers hypothesise that the exchange occurred during an ancient microbial interaction. Senior author Gregory J. Dick says: "There seems to have been an exchange of genes, which implicates the viruses as an agent of evolution. That's interesting from an evolutionary biology standpoint."

The findings are important as oxygen-starved zones are growing in the world’s oceans due to global environmental changes. This means that bacteria such as SUP05 and the viruses that prey on them are likely to expand their range. These bacteria may generate nitrous oxide, a greenhouse gas. It is important to gain a full understanding of the sulphur cycle and the bacterial-viral relationships.

Sources
Anantharaman, K., Duhaime, M. B., Breier, J. A., Wendt, K., Toner, B. M., and Dick, G. J. (2014). Sulfur oxidation genes in diverse Deep-Sea viruses. Science. http://dx.doi.org/10.1126/science.1252229 [Accessed 2 May 2014]

Press release: University of Michigan; available at http://www.eurekalert.org/pub_releases/2...042814.php [Accessed 2 May 2014]
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Hijack! Viruses plunder sulphur from deep-sea bacteria at hydrothermal vents00