Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics.

Polar marine ecosystems are very sensitive to effects of warming and temperature change because of the significant influence of sea ice on ecosystem dynamics. Rapid warming in the highly productive area of the Western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels ranging from ecosystem foundational microbes to high-level consumers such as krill and penguins. Microorganisms, especially in these locations are known to play significant roles in polar ecosystem changes and the abundance of key microorganisms are suggested to predict carbon cycling and climate feed backs on global-scale models. However, viruses are also known to play a substantial role in marine ecosystems through their alteration of microbial communities by causing bacterial mortality through viral infection and altering the biogeochemical cycling through the release of cellular contents via lysis. Recently published studies from a global-scale analysis of viromes suggest that viral diversity in this region is lower than that observed at lower-latitude locations. (Brum et al., 2015).

Despite the role these organism play, viral influences on microbial processes and ecosystem function remain highly unstudied in the Southern Ocean compared to other marine environments. Most studies focus on the spatial and temporal variability of community viral abundance via microscopy.

Quantitative examinations of these viral roles in nature is challenging, however, recent methodological advances through optimized sample-to-sequence pipeline are being used to generate quantitative double-stranded DNA (dsDNA) viral metagenomes (viromes). These new methods increase the knowledge of viral genomic diversity, niche differentiation and ecological drivers of variability.

Viral infections can either be lytic, where viral takeover of cellular machinery results in new viral progeny and lysis of the host or may involve a lysogenic stage in the case of temperate viruses where in viral DNA is maintained within the host as a prophage until induced to replicate lytically. Viruses in polar systems are thought to have diverse replication strategies that aid in the survival of the species in low temperature environments. The current paradigm based on cultivated temperate virus-host systems, is that they primarily utilise lysogeny when bacterial production is low (such as winter conditions) and switch to lytic replication when bacterial production increases (such as spring phytoplankton blooms), therefore temperate viral dominance offers a mechanism for survival in harsh winter conditions.

The data from this study compliments the long-term ecological research in the WAP (Ducklow et al, 2012) suggesting that temperate viruses play a very important role in modulating microbial driven processes in the biogeochemical cycle for this region.

Brum JR, Ignacio-Espinoza JC, Roux S, Doulcier G, Acinas SG, Alberti A et al. (2015). Patterns and ecological drivers of ocean viral communities. Science 348: 1261498.

Brum, J., Hurwitz, B. l., Schofield, O., Ducklow, H.W. & Sullivan, M.B (2016). Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics. The International Society for Microbiology Journal. 10, 437-449.