Links between viral and prokaryotic communities throughout the water column in the (sub)tropical Atlantic Ocean

Viral and prokaryotic abundance, production and diversity were determined throughout the water column of the subtropical Atlantic Ocean to assess potential variations in the relation between viruses and prokaryotes. Prokaryotic abundance and heterotrophic activity decreased by one and three orders of magnitude, respectively, from the epi- to the abyssopelagic layer. Although the lytic viral production (VP) decreased with depth, lysogenic VP was variable throughout the water column and did not show any trend with depth. The bacterial, archaeal and viral community composition were depth-stratified as determined by the automated ribosomal intergenic spacer analysis, terminal-restriction fragment length polymorphism and randomly amplified polymorphic DNA-PCR, respectively. Generally, the number of operational taxonomic units (OTUs) did not reveal consistent trends throughout the water column. Viral and prokaryotic abundance were strongly related to heterotrophic prokaryotic production, suggesting similar linkage strength between the viral and prokaryotic communities from the lower epi- to the abyssopelagic layer in the Atlantic Ocean. Strikingly, the prokaryotic and viral parameters exhibited a similar variability throughout the water column down to the abyssopelagic layers, suggesting that the dark ocean is as dynamic a system as is the lower epipelagic layer. It also indicates that viruses are apparently having a similar role for prokaryotic mortality in the dark oceanic realm as in surface waters. The more than twofold increase in bacterial OTUs from 2750 m depth to >5000 m depth and the concurrent decrease in viral OTUs, however, suggests that viruses might exhibit a wider host range in deep waters than in surface waters.