Viral impact on microbiology and geochemistry of extremely nutrient-depleted sediments

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Extremely oligotrophic mid-ocean gyres represent large parts of the world´s oceans, but were hardly explored, so far. The largest of these oceanic provinces, the South Pacific Gyre, was investigated during IODP Exp. 329. In this project, we will study the viral impact on the microbial communities and activities. Virus particles and total cell counts will be determined to estimate their global distribution within the subsurface. We will isolate aerobic and anaerobic prokaryotes and identify the prophages residing in their genomes. The morphologic and phylogenetic diversity of the phages will be analysed in detail. It will be studied whether viral lysis could provide limiting compounds to this extremely nutrient-depleted ecosystem. Thus, it should be clarified whether viruses might be the main controlling factor of the abundance and diversity of the deep biosphere communities. The results will be compared to our previous studies on benthic viruses from continental margin sites, and finally provide a more realistic estimate of the viral impact on the deep biosphere.