I ran across an interesting paper in PloS One published last month while looking up work done at the Venter Institute (see my post earlier this week).

It’s another paper describing some fascinating results obtained from the Sorcerer II Global Ocean Sampling Expedition (see their website here ). The project, which seeks to provide a glimpse into the vast microbial abundance and diversity in the oceans, has been publishing papers in open access journals and allowing the information collected on the voyage to being freely accessible in online databases. The results so far [1] have sent shockwaves throughout many scientific disciplines because we have drastically underestimated the microbial diversity on the planet.

The paper that I ran across actually examined the viral diversity in the ocean [2]. The reason it caught my eye was because I thought viruses couldn’t be that important in the ocean, let alone any ecosystem, when compared with microorganisms. They’re much smaller and aren’t technically alive (although that debate is for another post). After reading the first few lines of the abstract, this quote stood out to me:

“Interactions between viruses and their hosts impact several important biological processes in the world’s oceans such as horizontal gene transfer, microbial diversity and biogeochemical cycling.”

I thought for sure that this was just scientific ‘fluff,’ attempting to overemphasize the importance of the work. However, my naivety soon became apparent as I did some further reading in the paper and explored a few other papers in the literature.

As it turns out, viruses are indeed extremely important in many biogeochemical cycles. Among other things, They often control carbon cycling (due to cell lysis) and microbial diversity (by selecting for various hosts). Considering just their abundance alone (there are an estimated 10³⁰ viruses in the oceans and roughly 10⁷ viruses in one milliliter of ocean water), viruses account for a significant portion of biomass. And based on the latest results from the Sorcerer II, they are much more diverse than we ever thought (see figure above).

So, I was wrong. Nothing too surprising there. But, as someone who is interested in ‘the critical zone’ of our planet, I was curious for more information about the environmental impacts of viruses on other parts of the planet. What I found was circumstantial, but intriguing: According to some, there are a higher abundance of viruses in freshwater than marine water, and more associated with sediment than water [3]. That means that as amazing as the statistics are for marine systems, they could be even more impressive for subsurface ecosystems.

Unfortunately, however, there is no magic Sorcerer II sailing the underground seas collecting samples along the way. But I wonder how long it will be for a major genomic effort, such as that by the Sorcerer II in the oceans, directed towards identifying the microbial and viral diversity of the soils, sediment, and groundwater. Studies exist on smaller scales, for sure, but as the Sorcerer II is proving, we really have no idea what’s out there until we scale up dramatically. But who wants to play in the mud when they can sail the seas on a boat like this:

References:
[1] Rusch DB et al. (2007) The Sorcerer II Global Ocean Sampling Expedition: Northwest Atlantic through Eastern Tropical Pacific. PLoS Biol 5, e77. DOI: 10.1371/journal.pbio.0050077

[2] Williamson SJ, et al. (2008) The Sorcerer II Global Ocean Sampling Expedition: Metagenomic Characterization of Viruses within Aquatic Microbial Samples. PLoS ONE 3, e1456. DOI: 10.1371/journal.pone.0001456

[3] Filippini M, et al. (2007) Viral abundance and genome size distribution in the sediment and water column of marine and freshwater ecosystems. FEMS Microbiol. Ecol. 60, pg. 397-410. DOI: 10.1111/j.1574-6941.2007.00298.x

Further reading:
Weinbauer MG (2004) Ecology of prokaryotic viruses. FEMS Microbiol. Rev. 28, pg. 127-181. DOI: 10.1016/j.femsre.2003.08.001

Breitbart M, and Rohwer F (2005) Here a virus, there a virus, everywhere the same virus? Trends Microbiol. 13, pg. 278-284. DOI: 10.1016/j.tim.2005.04.003

Suttle CA (2005) Viruses in the sea. Nature 437, pg. 356-361. DOI: 10.1038/nature04160

Suttle CA (2007) Marine Viruses – major players in the global ecosystem. Nat. Rev. Microbiol. 5, pg. 801-812. DOI: 10.1038/nrmicro1750