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New findings on the genetic diversity of a virus community in an Antarctic lake


A multidisciplinary group of researchers from the Severo Ochoa Molecular Biology Centre (CSIC-UAM), the Universidad Autónoma de Madrid and the University of Valencia has described for the first time the genetic makeup of the community of viruses present in a lake in the Antarctic, which has been found to be one of the most diverse on Earth.


In this study, entirely funded by Spain and published in the journal Science, the researchers have identified the complex diversity of viruses of Limnopolar Lake, on the Byers peninsula (Livingston Island, Antarctic), a region in which the lakes are covered by ice during most of the year and there is very little influence from marine animals. According to the CSIC researcher who directed the study, Antonio Alcami: ‘These are very simple ecosystems, dominated by micro-organisms which have adapted to extreme environmental conditions: low temperatures, almost total darkness for most of the year, and very low levels of nutrients. They are biological systems living on the limit. Our description of the virus community present in an Antarctic lake is a first step to understanding better the part which viruses play in these extreme ecosystems, and if they have evolved independently during millions of years.’ The authors of this work have also identified new, small viruses which comprise the most abundant population when the lake is iced over, and have not been described in other natural settings. Evidence has also been found showing how the community of viruses present in this ecosystem varies over the course of the polar summer. Its composition is different when the lake is covered in ice and when the ice melts, indicating the ecological importance of the viruses in the ecosystem.

The Antarctic has been isolated for millions of years, with minimal impact by humans, and is considered one of the last pristine ecosystems on Earth. Recent studies show that viruses are the most abundant biological entities on the planet, and control the composition of communities of microbes. It has been estimated that there are billions of viral particles in every litre of seawater. However, the composition of the virus community in Antarctic ecosystems is completely unknown.

The researchers have obtained images of these viruses by electronic microscopy and have used new mass sequencing systems (Roche) to generate some 90,000 sequences of Antarctic viruses, offering us an overview of the genetic variety of viruses in these ecosystems (viral metagenome or viroma). ‘The results of the study are full of surprises. Although one would expect the biological diversity of polar environments to be low, in Limnopolar Lake we found an enormous diversity of viral genomes with about 10,000 species, distributed in the largest number of viral families found to date in natural environments’, explains Alberto López-Bueno, the first signatory to the article. While the aquatic systems described until now have been dominated by bacteriophages which infect bacteria, the Limnopolar lake contains a high proportion of viruses which infect eukaryotic organisms.

For the first time, the researchers used a metagenomic approach to describe how the viral population changes in different seasons. The drastic transition from an iced-over lake in spring to an open lake in summer gives rise to notable changes in the viral community, which goes from being mostly made up of small viruses with single DNA chains to being dominated by large viruses with double DNA chains, a phenomenon which the researchers believe coincides with a seasonal change in the hosts.

The Byers peninsula on Livingston Island is one of the few areas of the Antarctic which thaws in summer, and has been designated one of the Antarctic Specially Protected Area due to the great ecological value of its lakes and rivers. This project forms part of a multidisciplinary project called LIMNOPOLAR, which is studying the freshwater systems of the Byers peninsula. ‘The main aim of the LIMNOPOLAR project is to research the sensitivity of these non-marine aquatic ecosystems to climate change. The multidisciplinary research being carried out by Spanish and foreign scientists is making the Byers peninsula a landmark area for environmental studies in the Antarctic,’ says Antonio Quesada, a lecturer at the Universidad Autónoma de Madrid and the co-ordinator of the LIMNOPOLAR project.

This project was funded by the Spanish Polar Programme and the Antarctic expedition was made possible by the logistical support of the Marine Technology Unit (CSIC) and the Spanish navy's oceanographic research ship Las Palmas.

López-Bueno, Javier Tamames, David Velázquez, Andrés Moya, Antonio Quesada and Antonio Alcami. High diversity of the viral community from an Antarctic lake. Science 6 Nov 2009.

Fotos: Manuel Toro