Scientists Look to Antarctic Lakes for Answers About Marine Viruses

As the last glacial period came to an end about 10,000 years ago, the ice sheet covering Antarctica retreated and uncovered the coastal Vestfold Hills. Freed from the crushing weight of the ice, the land rose and the sea retreated. Valleys and depressions in the newly exposed land isolated some of the draining seawater. Today, more than 300 marine-derived lakes still dot this rocky region.

These lakes offer scientists a unique opportunity, as water was not the only thing left behind. Marine phytoplankton, bacteria, and viruses became landlocked as well, imprisoned in conditions they were not equipped to handle. And yet, they survived. Recent samples taken from the lakes have revealed communities of these organisms still living together in isolation after thousands of years.

Most of these lakes are ice covered; all are exposed to months of darkness. The phytoplankton that live there are trapped along with viruses that scientists know affect them. So, how have they survived in such a harsh environment? Why haven’t the viruses eventually wiped them out?

“We think that the viruses and phytoplankton in the lakes have evolved together, developing a mutually beneficial relationship that has helped them adapt to the extreme conditions,” said Senior Research Scientist Joaquίn Martίnez Martίnez. “We want to understand what organisms were trapped there, how they have changed, and how they differ from what currently lives in the open ocean.”

Martίnez will be analyzing samples that were previously collected from the Vestfold Hills by his collaborator Rick Cavicchioli from the University of New South Wales. The physical and chemical properties of each lake have evolved over time as well, and he will focus on three lakes that represent the varieties of water chemistry, salinity, and stratification in the region. One targeted lake is ice-free for four months of the year; one is ice-free for six weeks; and one is so salty it never freezes.

The lakes’ physical isolation and captive communities offer a level of simplicity and control that scientists can carefully create in a lab but rarely find in the field. This provides an opportunity to study the very complex interaction between viruses and phytoplankton, which can be difficult to characterize in most environments.

“We’re using these lakes like natural laboratories,” Martίnez said. “When you study samples from the ocean, there are so many viruses and plankton that it can be very difficult to identify the players, let alone tease apart who is infecting whom. The insights we gain into the role of viruses in these lakes may allow us to then understand what is happening in more complex environments.”

Marine viruses are incredibly abundant and play important roles in maintaining balance and recycling nutrients throughout the ocean. However, scientists know relatively little about the mechanisms through which they influence organisms’ evolution and help shape life on our planet.

Three types of viruses that infect phytoplankton have already been identified in samples from the lakes. As viruses can transfer genes between hosts, Martίnez plans to investigate the role this may have played in the algae’s long-term adaptations. He also aims to understand how interactions between the three viruses may be helping the phytoplankton to survive.

To answer these questions, he plans to genetically sequence samples that were collected from the lakes over a period of three years. He will use metagenomics to look at the genetic makeup of the community as a whole, and he will also isolate single viruses from some of the samples and sequence their individual genomes. He is currently hiring a postdoc to help generate and analyze the data, all of which will be made publically available to other researchers through the U.S. Department of Energy’s Joint Genome Institute.

“We hypothesize that interactions between the viruses trigger a persistent infection of the host that actually protects it from being killed,” Martίnez said. “While viruses are commonly viewed as a challenge to a community, I think we will find that they are a key reason the phytoplankton in these lakes have survived and thrived for thousands of years.”