The deep sea is the largest ecosystem on Earth, but despite its size it is one of the least explored. While benthic systems such as hydrothermal vents, cold seeps, and sediments have received attention, the deep pelagic biome is less understood. Viruses have repeatedly been recognized to play a bigger role in ecosystems than previously assumed, e.g. in their impact on biogeochemical cycles and on community structures by ending bloom events and facilitating nutrient availability through lysis. Giant viruses have been studied intensively in the surface ocean. However, deep sea pelagic systems remain understudied in terms of viruses. Here, we used a unique in-situ incubation system to introduce detrital phytoplankton material to the natural microbial community in the pelagic deep sea, 1040 m below sea level. Over the course of the experiment, taxonomic composition of the resident microbes shifted, in particular by the 4-month time point. Metagenomic sequencing and assembly recovered multiple giant virus genomes. Phylogenetic reconstructions indicate that several of these viruses represent new viruses that are relatively distant within known giant viruses. Similarly, initial analyses indicate presence of auxiliary metabolic genes encoding functions not yet known in giant viruses.

Primary Presenter: Theo Krüger, GEOMAR Helmholtz Centre for Ocean Research Kiel (tkrueger@geomar.de)

Authors:

Theo Krueger,   ()

Yu-Chen Ling,   ()

Fabian Wittmers,   ()

Rachel Harbeitner,   ()

Alexandra Worden,   ()