Abstract
The aim of this study was to compare the composition of two deep-sea viral communities obtained from the Romanche Fracture Zone in the Atlantic Ocean (collected at 5200 m depth) and the southwest Mediterranean Sea (from 2400 m depth) using a pyro-sequencing approach. The results are based on 18.7% and 6.9% of the sequences obtained from the Atlantic Ocean and the Mediterranean Sea, respectively, with hits to genomes in the non-redundant viral RefSeq database. The identifiable richness and relative abundance in both viromes were dominated by archaeal and bacterial viruses accounting for 92.3% of the relative abundance in the Atlantic Ocean and for 83.6% in the Mediterranean Sea. Despite characteristic differences in hydrographic features between the sampling sites in the Atlantic Ocean and the Mediterranean Sea, 440 virus genomes were found in both viromes. An additional 431 virus genomes were identified in the Atlantic Ocean and 75 virus genomes were only found in the Mediterranean Sea. The results indicate that the rather contrasting deep-sea environments of the Atlantic Ocean and the Mediterranean Sea share a common core set of virus types constituting the majority of both virus communities in terms of relative abundance (Atlantic Ocean: 81.4%; Mediterranean Sea: 88.7%).
Highlights
The deep ocean is characterized by the absence of light, high pressure, low temperature, high inorganic nutrient concentrations, and a dominance of recalcitrant organic matter [1]
The number of virus types uniquely found in the Atlantic Ocean (431 unique virus genomes) was much higher compared to the Mediterranean Sea (75 unique virus genomes), their contribution to the overall relative abundance was small and comparable in both viromes (Fig. 3)
Methodological considerations the sample volume for the Mediterranean Sea virome was 3.8-times larger and viral abundance was twice as high compared to the Atlantic Ocean (Table 1), we found 1.8-times more distinct archaeal and bacterial virus genomes in the Atlantic Ocean (786 archaeal and bacterial virus genomes) compared to the Mediterranean Sea virome (432 archaeal and bacterial virus genomes)
Summary
The deep ocean is characterized by the absence of light, high pressure, low temperature, high inorganic nutrient concentrations, and a dominance of recalcitrant organic matter [1]. Prokaryotic and viral communities in deep waters of the Mediterranean Sea display seasonality and are as dynamic as in the surface waters [4,5,6]. Viruses, especially those infecting prokaryotes, are the most abundant biological entities in marine environments and enhance dissolved organic matter cycling due to lysis of their prokaryotic host cells [7,8,9]. Metagenomic studies have revealed that viruses carry a high proportion of unknown open reading frames [18]
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