Giant viruses found in Austrian sewage fuel debate over potential fourth domain of life

Frederik Schulz, a postdoc at the Department of Energy Joint Genome Institute in Walnut Creek, California, and colleagues weren't planning to test the fourth domain scenario when they teamed up with Austrian scientists to investigate the microbes residing in sludge from the Klosterneuburg plant. They used a method known as metagenomics, which involves sequencing all the DNA in a sample to identify the genomic fingerprints of new organisms, rather than directly isolating cells or viruses. Viral DNA fragments kept turning up. When the team assembled some of these fragments into a genome, they concluded that it belongs to a new giant virus, which they named Klosneuvirus. By applying the same techniques to samples from other locales, the team pieced together genomes of three kindred viruses.

These Klosneuviruses stood out because their genomes are more cell-like than those of any previous giant viruses. For example, cells stitch together proteins from 20 types of amino acids, and each has a different enzyme that affixes it to a carrier molecule for delivery to sites of protein synthesis. Other giant viruses carry genes for seven varieties of the attachment enzymes, but between them the Klosneuviruses have genes for all 20.

[link to www.sciencemag.org]