Antarctic sea is loaded with unknown viruses

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A small inflatable boat carrying researchers moves through icy water scattered with floes, heading toward a towering, snow-covered mountain with dark rock faces under a cloudy Antarctic sky.

Out of thousands of marine viruses that were discovered in Antarctic waters in the past two years, 75 percent was new to science. That is shown in a paper that was published in Nature Communications on 24 October 2024, by NIOZ PhD candidate Gonçalo Piedade and colleagues. “This project has identified an enormous number of pieces in the important jigsaw of viral ecology and, therefore, in the circle of carbon in the oceans and the climate system”, says Professor Corina Brussaard of NIOZ and the University of Amsterdam.

A person in an orange cold-weather survival suit sits on a small boat surrounded by floating sea ice, smiling and giving two thumbs up during a sample-collection outing on an overcast polar morning.

Out on the boat in another morning of sample collection. (photo: Ella Wesdorp)

For his research, Piedade and colleagues sampled the Antarctic waters near the British Research Station Rothera. After filtering the tiny virus particles out of the water, they performed genetic analyses in the Dutch ‘Dirk Gerritszlab’, that is hosted by the British station. Many of the viruses they found in the Antarctic seawater (about 200 million per glass of seawater) were different from already known marine viruses.  “Out of approximately 8.000 virus genome sequences, 75 % at the species level were not present in the databases, highlighting just how unique and unexplored the Antarctic environment truly is”, says Piedade.

Key role

Based on their differences and similarities to known viruses, Piedade also tried to link the viruses to potential hosts. “These host are often single celled algae and bacteria”, he explains. “We also found a strong seasonality in the viruses. The algal bloom at the start of  the Antarctic summer ‘kick-starts’ a whole lot of microbiological activity. Following the algal hosts over time, we saw the levels of their specific viruses rise as well, showing how these viruses play a key role in controlling the microbial population.”

Giant viruses

With thousands of different viruses present, Piedade and colleagues found that a specific group of viruses appeared key in the circle of algal life in the ocean. Piedade was particularly thrilled by the relatively high number of so-called ‘giant viruses’. “They show a very strong seasonality and were often linked to eukaryotic algae.”

Flow of carbon and nutrients

Professor Brussaard, the supervisor of the research by Piedade, is very content with the pieces he added to the puzzle. “Antarctica is particularly sensitive to climate change. The food web here also starts with algae, the primary producers, and ends with fish and fish-eating birds and marine mammals. So, the viruses controlling the bloom or decay of algae, play a pivotal role here.”

By killing the single-celled algae and bacteria, viruses redirect the flow of carbon and nutrients, Brussaard explains. “They determine whether the carbon that is captured by algae may sink to the bottom of the ocean, stay in the food chain through grazing, or end up as dissolved organic matter by viral infection which stimulates microbial degradation and recycling. If we want to understand what global warming does to that system, we need to know who the players are in the first place.”

A researcher in a white lab coat works at a computer beside flow-cytometry equipment, with snowy Antarctic mountains and the red research vessel RV Laurence M. Gould visible through the window behind them.

Quantifying microbial abundances using flow cytometry with a view of the RV Laurence M. Gould. (photo: Ella Wesdorp)