A study published in BioMed Central's Biology Direct journal reports the existence of a previously undetected group of viruses and, more importantly, a new type of viral genome that could have huge implications for theories of viral emergence and evolution.
Viruses are the most abundant organisms on earth, yet little is known about their evolutionary history since they have exceptionally high rates of genetic mutation which are difficult to track. Viral metagenomics, however, is becoming an increasingly useful tool with which to glimpse virus evolution, as it makes available vast amounts of new sequence data for analysis.
Kenneth M Stedman's team from Portland State University in Oregon, USA, used a metagenomics approach to investigate virus diversity in Boiling Springs Lake in Lassen Volcanic National Park, USA, an acidic, high temperature lake (ranging from 52-95°C, with a pH of ~2.5) that sustains a purely microbial ecosystem.
Astonishingly, they found a unique viral genome that has never before been reported -- a circular, single-stranded DNA virus encoding a major capsid protein seen previously only in RNA viruses. This unusual genome provides proof that integration of an RNA virus into a DNA virus may have occurred between two unrelated virus groups at some point in evolution -- something that has not been observed before. Moreover, this suggests that entirely new virus types may emerge via recombination of functional and structural modules between vastly different viruses, using mechanisms that are as-yet unknown
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