A new study by University of British Columbia and US Department of Energy Joint Genome Institute researchers sheds light on the ecological role played by marine viruses in oxygen starved regions of the worlds' oceans.
It's the first time researchers have used single cell genomics to explore interactions between SUP05—a sulfur-oxidizing bacteria that will play an increasingly important role in ocean carbon and nutrient cycling—and the viruses that infect the bacteria at deeper depths.
The take away: Marine viruses appear to be much more important to microbial ecology below sunlit surface waters than researchers previously suspected.
"What we’re ultimately interested in understanding is how different microbial groups interact to drive carbon, nitrogen and sulfur cycling in oxygen minimum zones," says UBC microbiologist Steven Hallam, co-author of the paper published in the journal eLife.
"SUP05 is a hub for metabolic coupling in OMZs. By studying viruses that infect SUP05, we’re beginning to recognize that viruses can alter the network properties of microbial communities with resulting feedback on nutrient and energy conversion processes, including the production and consumption of climate active gases. Given that a third of SUP05 cells may be infected at any given time, to what extent is carbon fixation and energy metabolism modulated by viral lysis or reprogramming?"
The study isolated 69 viruses representing five new genera in bacterial samples from Saanich Inlet. The inlet, a seasonally oxygen deficient fjord on the coast of Vancouver Island, British Columbia, is a natural laboratory for studying OMZs.
"This study represents the first of its kind, exploiting the unique strength of single-cell genomics to explore virus-host dynamics, including viral co-infections, in a completely cultivation-independent manner,” says US Department of Energy researcher Tanja Woyke, co-author of the study. “The resulting data provide a very robust foundation for future experimental work.”
In the study, the team collected several thousand individual bacterial cells from three depths spanning the Saanich Inlet oxygen gradient (at 100, 150 and 185 meters). Nearly 130 SUP05 single amplified genomes (SAGs) were recovered from this collection by the Bigelow Laboratory for Ocean Sciences and sequenced at the Genome Sciences Centre in Vancouver British Columbia. The sequences were then assembled, quality checked and annotated at the DOE JGI.
For multicellular life—plants and animals—to thrive in the oceans, there must be enough dissolved oxygen in the water. In certain coastal areas, extreme oxygen-starvation produces 'dead zones' that decimate marine fisheries and destroy food web structure. As dissolved oxygen levels decline, energy is increasingly diverted away from multicellular life into microbial community metabolism resulting in impacts on the ecology and biogeochemistry of the ocean.
Over the past 50 years, oxygen minimum zones (OMZs) have expanded due to climate change and increased waste run-off from farms and cities. There are currently more than 500 OMZs worldwide, encompassing roughly eight percent of ocean volume that is considered oxygen-starved. Microbial community metabolism in these oxygen-starved waters directly impacts nutrient and energy conversion processes, including the production and consumption of the greenhouse gases carbon dioxide, methane, and nitrous oxide. Knowing how microbial interactions change in response to OMZ expansion is crucial to understanding the organizing principles underlying coupled nutrient and biogeochemical cycling in the ocean and the balance of greenhouse gases in the atmosphere.
Ecology and evolution of viruses infecting uncultivated SUP05 bacteria http://elifesciences.org/content/early/2014/08/29/eLife.03125