Chief Science Correspondent
When many people think of the profound effects of climate change in polar ecosystems, they will often voice concerns on the effects of warming on large, charismatic animals (think: penguins and polar bears).
But many will overlook the importance of microbes, such as bacteria and viruses. These organisms may not be visible to the naked eye, but they often play critical roles in nutrient cycling, animal physiology and decomposition. Viruses can impact microbial dynamics by causing bacterial mortality. However, the dynamics of Antarctic viruses are not yet fully understood.
Viruses replicate using one of two strategies: lysis, in which infection leads to immediate microbial death; or lysogeny, in which the viruses remains in the bactieral host as it continues to replicate. Southern Ocean microbes are active during the spring and summer, following the annual spring melt. As the Southern Ocean becomes warmer, however, the extent and duration of sea ice may decline.
Jennifer Brum, the first author of the paper, said in an interview that these results were striking, because the shift between replication strategies occurred within one week. This shift correlated with the annual phytoplankton bloom, which results in increased bacterial abundance.
Using metagenomic analyses, the team found that temperate viruses (that is, viruses capable of both lytic and lysogenic replication strategies) dominate the WAP ecosystem. Brum said the data indicate a "boom or bust" model.
Essentially, increased temperatures in the spring prompt sea ice melt, which results the formation of a phytoplankton bloom. Bacteria consume the bacterial matter and increase in abundance. Then, the viruses within the bacteria replicate lytically, killing the bacteria.
Brum explained these viruses employ lysogenic replication during the winter. By waiting until the spring to lyse their hosts, the viruses can increase in abundance alongside the increasing bacteria.
“It’s basically a way for viruses to ‘overwinter,'" Brum said. "Viruses reside in their hosts until they become more productive.”
Brum predicted that over time, as the water temperatures around the WAP increase, these dynamics may shift to resemble non-polar ecosystems. She said that Hugh Ducklow, another author on the paper, has demonstrated that the sea ice extent and duration has declined in recent years. The loss of sea ice promotes increased mixing of the water column and is thus likely to decrease bacterial productivity, Brum said the viruses may remain in the host, rather than switch to lytic replication.
"You wouldn't get tha 'boom and bust,'" Brum said. "I think the relationship between primary producers, bacterial production and viral infection may change dramatically."
To learn more about Brum's research, visit her website here.