Metagenomics of the Ocean's Viral Species

The ocean is full of life—large, small, and microscopic. Bacteriophage (phage) viruses are minute, self-replicating bundles that alter microorganisms’ genetic material and moderate their communities through predation and parasitism. Despite their small size, they are astoundingly abundant with about as many of them in a bucket full of seawater as there are humans on the planet. As a result, they can have a huge impact ecologically.

In a new study published online this week in the open access journal PLoS Biology, Florent Angly, Forest Rohwer, and colleagues detail their metagenomic study of the diversity of bacteriophage present in water samples collected from 68 sites over 10 years from four oceanic regions (the Sargasso Sea, the Gulf of Mexico, British Columbia coastal waters, and the Arctic Ocean). They use pyrosequencing (a technique that enables collection of many DNA sequence reads for less cost than conventional sequencing) to large samples, rather than individual organisms to gain insights into diversity, geography, taxonomy, and ecosystem functioning. This approach identified tremendous viral diversity with greater than 91% of DNA sequences not present in existing databases.

Angly and colleagues analyzed the distribution of marine phages among the sampling sites and found a correlation between geographic distance and genetic distance of viral species, supporting the idea that the marine virome varies from region to region. They also investigated how similar the viromes from each location were—in fact, the differences were mostly explained by variations in relative abundance of the viral species, and supports the notion that although everything is everywhere, the environment selects.

Overall, they saw that samples from the British Columbia coast were the most genetically diverse (consistent with its nutrient-rich environment). The other three samples showed increasing diversity with decreasing latitude, a trend that parallels previous findings from terrestrial ecosystems. In fact, the researchers predict that the world’s oceans hold a few hundred thousand broadly distributed viral species, with some species-rich regions likely harboring the majority of these species.

Citation: Angly F, Felts B, Breitbart M, Salamon P, Edwards R, et al. (2006) The marine viromes of four oceanic regions. PLoS Biol 4(11): e368. DOI: 10.1371/journal.pbio.