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Migrate on Vapors among Yellowstone Hot Springs

Viruses in acidic hot springs at Yellowstone National Park appear to migrate on steam droplets, sometimes traveling up to 20 miles between pools. The unexpected finding helps to explain how such viruses spread far and wide, according to molecular microbiologist Frank Roberto of the Idaho National Laboratory (INL), Idaho Falls, virologist Mark Young at Montana State University (MSU), Bozeman, and their collaborators. These findings emerged during a twoyear survey of microbial diversity in those hot springs, part of the National Science Foundation Microbial Observatories Program. The researchers were investigating how changes in water geochemistry and host populations affect viral populations. “We thought viruses would be a quick sensor of the environment,” says Young. Members of the research team collected samples of water about every 30 days for two years from the Crater Hills, Ragged Hills, and Rabbit Creek hot springs, each of which is situated in distinct geological regions within Yellowstone. “There’s a lack of awareness that viruses exist in Yellowstone thermal pools,” says Roberto of INL. Members of his laboratory sequenced the genomes of various Sulfolobus spindle-shaped viruses (SSV) and Sulfolobus islandicus rod-shaped viruses (SIRV). These DNA-containing viruses infect Sulfolobus, one of the best characterized of the archaea microbial species discovered in Yellowstone 35 years ago. From 2,165 independent SIRV clones, the researchers identified 722 unique sequences representing 12 distinct clades, five of which were common to all three hot springs. Meanwhile, 300 unique sequences of SSV formed six distinct clades, with three of them common to all three hot springs. In surveys of viral abundance at the three hot springs, some clades proved to be in rapid flux. Thus, seemingly dominant SIRV and SSV clades seemed to disappear and then reappear within days. These viral fluctuations did not correlate with any visible changes in geochemistry, and were too extreme and rapid to attribute to mutations. “We didn’t know what to make of the surprising data,” Young says. However, when ecological models were applied to those data sets, the patterns suggested that viruses were migrating from one hot spring to another, according to their collaborator Matthew Lavin, a botanist who studies biodiversity at MSU. Although Yellowstone has plenty of underground waterways, the researchers ruled them out as potential conduits for viruses because the temperatures in the waterways can exceed 400°C, which would be lethal even for the hardiest thermophiles. That left steam as the likely means for transporting viral particles between hot springs. Indeed, the researchers detected viruses in air columns above hot springs. Additional details are described the November 19, 2007 Proceedings of the National Academy of Sciences. “Few virologists have combined phylogeny with ecological models,” Young says, and virologists would be more inclined to attribute fluctuating