An entirely new type of virus!

Viruses are the most abundant organisms on earth (if they can be called organisms). However we know little about their evolutionary history due to extremely high rates of genetic mutation. Viral metagenomic studies are becoming an increasingly frequent method for attempting to describe viral evolution. In this paper, the authors describe a completely new and unique viral genome that has never been seen before. The original aims of the paper were to investigate viral diversity in Boiling Springs Lake, Oregon, USA, which is a high temperature (52-92 degrees C), low pH (~2.5) extremophilic environment. In order to do this, metagenomic techniques, including inverse PCR, were used. 

To the authors’ apparent surprise, a unique viral genome was found. This consisted of a circular, single-stranded DNA virus encoding a major capsid protein which previously only had been seen in RNA virus’s. This was seen as confirmation that RNA virus may integrate into DNA virus’s and that this has happened at some point in the evolutionary timescale of virus’s. The genome is exceptionally large and roughly double the size of typical circoviruses, with an uncommon arrangement of open reading frames. The authors state that this type of virus may be widespread in the marine environment, but also can be potentially be widespread in freshwater environments as well. 

This is an exciting study that reports the discovery of an entirely novel entity, a cross breed (or chimera) between a ssDNA circovirus and a Tombusvirus-like RNA virus.

The study concludes that these results have huge implications on the early evolution of viruses and significantly extends the modular theory of virus evolution and I would agree with them, whilst metagenomic studies have their advantages and disadvantages (identification of anything, even if it at a low abundance, however the identification is rarely of a high standard) this paper crucially shows convincing evidence of the novel virus by inverse PCR of an independent environmental sample. However, the authors do not give any solid explanation as to how the proposed inter-viral recombination arose but do speculate that a DNA circovirus-like progenitor may have acquired a capsid protein gene from a ssRNA virus via reverse transcription and recombination. Nevertheless this is a very intriguing paper and just goes to show that there are still new organisms left for us, the next generation of microbiologists, to find!

REF: Diemer & Stedman (2012) A novel virus genome discovered in an extreme environment suggests recombination between unrelated groups of RNA and DNA viruses. Biology Direct, 7, 13.
ACCESSED FROM: http://www.biology-direct.com/content/7/1/13