Mobile microbes: viruses living in Yellowstone’s hot springs travel near and far

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Date:26 November 2007 Tags:,

Viruses living in the hot springs of Yellowstone National Park (YNP) are surprisingly mobile – migrating between Yellowstone hot springs and possibly even reaching worldwide locations, according to a new study. The discovery of the mobility of these extremophiles adds an important new dimension to a growing body of evidence of the ability of viruses, which are the largest reservoir of genetic material on Earth, to move independently of their hosts.

The study of the YNP hot spring viruses, which was funded by the National Science Foundation (NSF), “is helping to blow out of the water the concept that viruses always have an intimate relationship with their hosts,” says Lita Proctor, an NSF programme director.

According to Proctor, the study shows that even some viruses that live in the extreme and specific conditions of YNP hot springs, where the temperature and pH are comparable to those of boiling battery acid, may travel far from their host cells and maintain their viability outside of host cells for significant periods of time.

Because viruses are the largest reservoir of genetic material on earth and because their life’s work is to transfer genes from one population to another, their mobility has important implications for evolution and ecology.

The study of the YNP hot spring viruses was conducted by researchers from Montana State University and Idaho National Laboratory and was published in the online edition of the Proceedings of the National Academy of Sciences during the week of 12 November 2007. The study involved sampling the geochemistry, microbial host populations and diversity of the populations of two virus families in three YNP hot springs every 30 days for two years.

“No one had ever before looked at the dynamics of a viral type – how it changes over time,” says Mark Young, the study’s principle investigator. “Because each hot spring acts like a geographically isolated island, we could study how the populations of viruses in these hot spring changed over time.”

Results from the study showed that the geochemistry and microbial host populations of the hot springs remained relatively stable throughout the study period. But “the viruses moved between the hot springs in a very random way,” says Young. Analyses of the DNA sequences of these viruses together with ecological modelling indicated that these population changes resulted from the migration of viruses between hot springs, not from in-situ genetic mutations of the viruses. These results show that virus immigration rather than mutation can determine the structure of communities of viruses.

How can the viruses move between hot springs that are kilometres apart from one another? The researchers detected the presence of the viruses in the air column above the hot springs – a finding that implies that the viruses travel in droplets of steam. (However, some migration via subterranean streams in YNP is also possible.)

It is unknown how far YNP’s hot spring viruses travel. But the researchers did discover that these viruses are included in a huge catalogue of microbes found in the Sargasso Sea off Bermuda that was published in 2004. Because these YNP viruses are currently only known to replicate in hosts requiring the extreme conditions of hot springs, the scientists believe that these wayward viruses were probably immigrants – not permanent, replicating residents of the Sargasso Sea. Therefore, their presence in the Sargasso provides evidence of their long-distance mobility.

Young says that viruses are the most common biological entity on Earth, but only about 0,001 per cent to 0,1 per cent of those that exist on Earth have, so far, been identified. “There is a huge pool of viruses out there that can move in and out of an environment.”

And as Young’s study shows, today’s dominant member of a viral community can be tomorrow’s viral has-been.

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