Metagenomic analysis of hadopelagic microbial assemblages thriving at the deepest part of Mediterranean Sea, Matapan-Vavilov Deep

The marine pelagic zone situated >200m below the sea level (bls) is the largest marine subsystem, comprising more than two-thirds of the oceanic volume. At the same time, it is one of the least explored ecosystems on Earth. Few large-scale environmental genomics studies have been undertaken to examine the phylogenetic diversity and functional gene repertoire of planktonic microbes present in mesopelagic and bathypelagic environments. Here, we present the description of the deep-sea microbial community thriving at >4900m depth in Matapan-Vavilov Deep (MVD). This canyon is the deepest site of Mediterranean Sea, with a deepest point located at approximately 5270m, 56km SW of city Pylos (Greece) in the Ionian Sea (36°34.00N, 21°07.44E). Comparative analysis of whole-metagenomic data revealed that unlike other deep-sea metagenomes, the prokaryotic diversity in MVD was extremely poor. The decline in the dark primary production rates, measured at 4908m depth, was coincident with overwhelming dominance of copiotrophic Alteromonas macleodii'deep-ecotype' AltDE at the expense of other prokaryotes including those potentially involved in both autotrophic and anaplerotic CO2 fixation. We also demonstrate the occurrence in deep-sea metagenomes of several clustered regularly interspaced short palindromic repeats systems. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.