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Arctic giant viruses offer climate change clues

Viruses are key to understanding polar aquatic ecosystems.

Mt Herschel (3335m asl) from Cape Hallet with Seabee Hook penguin colony in Foreground. Antarctica. Credit - Andrew Mandemaker. (CC BY-SA 2.5)
Mt Herschel (3335m asl) from Cape Hallet with Seabee Hook penguin colony in Foreground. Antarctica. Credit - Andrew Mandemaker. (CC BY-SA 2.5)

Microbiologists from Université Laval, Québec, have been studying giant viruses in climate-endangered Arctic Epishelf Lake. There is an abundance of the viruses in the Milne Fiord Epishelf Lake near the North Pole. The lake is located some 500 miles from the North Pole.

An interesting fact about the lake is that it is a rare freshwater lake, floating atop the Arctic Ocean. The lake is held in place by a coating of ice. The lake contains a mixture of marine, freshwater, and brackish Zooplankton taxa.

Microbiologically, what is of interest is that the lake is dominated by single-celled organisms like cyanobacteria. These bacteria are infected by atypical “giant viruses”. These viruses are important for understanding polar aquatic ecosystems. Most of its viruses remain unknown and they are traceable only from fragments of their sequences, having large, pseudo-icosahedral capsids (200 to 400 nanometers in diameter).

By charting the diversity and distribution of these giant viruses provides insights into the lake’s ecology. However, the researchers are racing against time since quickly rising temperatures are limiting the period available to fully understand the biodiversity and biogeochemical cycles of the ice-dependent environments.

The increasing temperature is causing the ice shelf that holds the lake in place to deteriorate and at one stage the lake will drain into the Arctic Ocean and be lost. Mixing seawater with freshwater lake will mean a loss of biodiversity.

The lake is classed as a halocline (a strong, vertical salinity gradient within a body of water). This is an area where salinity falls quickly providing niches for viruses that are found neither in freshwater nor marine layers of uniform salinity.

In the meantime the researchers are sequencing DNA recovered from within the lake water, enabling them to identify the viruses and microorganisms within it. This provides insights into the viral ecology in diverse global environments. This includes understanding the lytic lifestyle, which refers to the release of daughter virus particles as host microbial cells are destroyed.

The data gathered to date indicates a multiyear decline in the abundance of cyanobacteria. This is the product of increasing marine influence in the freshwater lake, something that arises because cyanobacteria have very low abundance in the Arctic Ocean.

The research appears in the journal Applied and Environmental Microbiology, titled “Climate-Endangered Arctic Epishelf Lake Harbors Viral Assemblages with Distinct Genetic Repertoires.”

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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