Factors influencing viral distribution and abundance along a latitudinal transect of the North Atlantic Ocean at different depths.

It is estimated that there are 10³⁰ viruses in the ocean (approximately 10 times as many as bacteria). Viruses are not just abundant in number they are also genetically diverse.  They influence the composition of marine communities and play an important role in biochemical cycles. Moreover viruses control microbial mortality and may help maintain diversity.

The study by De Corte et al. (2012) looked at the factors controlling viral distribution, abundance and production to assess the potential variations in the relationship between viruses and prokaryotes across a latitudinal transect in the North Atlantic Ocean.

This study is important because currently most published material on virus-prokaryote interactions in marine environments focus on near shore waters whereas in this case a wider area over 4 North Atlantic provinces in different pelagic zones are used.  

Many factors may influence distribution of viruses throughout the ocean but in the end viral distribution depends on the availability of suitable host therefore both prokaryote production and abundance were measured as well as viral production and abundance. The aforementioned factors were assessed throughout the water column and at different depth to determine the potential variations in interactions. Samples were obtained from 24 depths at 33 stations from 5 different pelagic zones. Prokaryote and viral abundance was measured using flow cytometry standard procedure. Samples were stained with SBYR Green I (a fluorescent dye) after being shock frozen with N₂. Viral production was measured using the dilution approach. Prokaryote production was measured using an assay for radioactively labelled leucine incorporation. Radio activity of the samples and a blank were measured and after basic calculations the results were converted into the incorporation rate.

Results showed a significant decrease in abundance of viruses and prokaryotes with depth over all stations (abundance was negatively related to depth) Prokaryote production also decreased with depth. Lytic viral production decreased and lysogenic production stayed the same. Multivariate regression analysis was used to predict the factors explaining the variability of viral abundance between the different depths. Taking the whole data set into consideration the variation was mainly explained by prokaryote abundance, temperature and latitude which together accounted for 73% of total variation. Prokatyote abundance alone accounted for 46% of the variation in abundance.  Temperature and prokaryotic abundance were seen to be the main factors influencing the differences in viral abundance between the 4 provinces, 2 mainly influenced by temperature and 2 by viral abundance. Based on the above results by De Corte et al. (2012) concluded that virus-host interactions significantly change in different oceanic provinces in response to biological factors i.e. host availability but also to chemical and physical factors in the environment.

De Corte, Daniele Sintes, Eva Yokokawa, Taichi Reinthaler, Thomas Herndl, Gerhard J (2012) Links between viruses and prokaryotes throughout the water column along a North Atlantic latitudinal transect. The ISME Journal (2012) 6, 1566–1577.

http://www.nature.com/ismej/journal/v6/n8/full/ismej2011214a.html