Science journalist Jane Qiu has now reached the Palmer ecological research station on the Antarctic Peninsula, joining researchers investigating how climate change has affected the region in recent decades. Please check back for her dispatches from the bottom of the world.
Cold rooms seem redundant in the Antarctic. But that’s where Christopher Schvarcz spends most of his working hours at the Palmer ecological research station in western Antarctic Peninsula. Looking into a microscope, he is transferring individual phytoplankton – single-celled plants that are the starting point of the marine food chain – into a flat plate with 96 wells, each about seven millimetres in diameter.
A second-year PhD student at the University of Hawaii in Manoa, Schvarcz will let the isolated phytoplankton proliferate for a few weeks, to create cell cultures that originate from single cells. He will then infect the cultures with viruses collected from sea water around the station. Ultimately, Schvarcz and his colleagues want to identify virus strains that infect known types of phytoplankton.
“There are about one billion viruses in one litre of sea water,” says Alex Culley, a marine virologist also at University of Hawaii at Manoa. “They infect all organisms, from bacteria to whales, but we know almost nothing about them.” To date, scientists have identified only four virus strains that infect diatoms, the predominant type of phytoplankton in the region, and two that infect dinoflagellates – one of several types of microscopic, floating plants that take over after diatom blooms end.
Viruses affect how carbon is transferred through the marine food chain and are important for nutrient recycling and the global carbon cycle, says Culley. Viral infection, for instance, can destroy phytoplankton cells and terminate the blooms. This could produce a large amount of dissolved organic matter that can be consumed only by bacteria, shortcutting the flow of nutrients from phytoplankton to the animals that graze on them.
Bacteria convert a quarter of ingested organic carbon into their biomass and pump the rest back to the atmosphere in form of carbon dioxide – a byproduct of respiration, in which nutrients are turned into useful energy in the cell.
The boost in bacterial growth and carbon emission, however, is countered by viral infection and by microscopic marine animals that graze on bacteria.
Culley came to the station also to solve a puzzle that has been confounding Palmer researchers. Samplings and research at the station in the past decade show that bacterial production in the region’s coastal waters constitutes only 5% of the primary production – the light-driven process of converting carbon dioxide into organic matter by plants, the starting point of the food web. This compares to 15-30% elsewhere in the global ocean – making western Antarctic Peninsula an important region of carbon storage.
Culley suspects that viral infection may be one of the reasons why levels of bacteria in the region are so low. To investigate, the team will measure the viral production rate in bacteria and phytoplankton in sea water samples. Using transmission electron microscopy, they will count the percentage of visibly infected cells and the average burst size – the number of viruses released by the cell when it lyses. These data should give the researchers a rough estimate of the percentage of bacteria and phytoplankton hosts that are infected by viruses.
Meanwhile, Jennifer Brum, a marine virologist of the University of Arizona at Tuscon, is interested in how the viruses make it through the winter. In the dark, prolonged Antarctic winter, it is extremely cold and the primary production is at its minimum. Viruses can enter a dormant phase called lysogeny, in which they integrate their genetic material into the host genome, and Brum wants to know how the proportion of viruses in this phase varies with season and changing environment.
The studies carried out at Palmer will be complemented by a project to sequence the genetic material of the entire viral community sampled at Palmer and brought back to the US. “This will allow us to identify the most abundant viruses and their roles in the ecosystem,” says Culley.
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This is my last blog during this once-of-the-lifetime research trip in the Antarctic. Tomorrow, I will board the R/V Laurence M. Gould and head back to Punta Arenas in Chile. Thank you for coming along.
Previous posts:
Probing ocean acidification
Images:
Christopher Schvarcz collects sea water samples for virus studies / Jane Qiu
Alex Culley prepares for experiments to measure viral production / Jane Qiu