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Census of Deep Life

Abstract

The Haakon Mosby mud volcano (HMMV), located on the continental margin in the Barents Sea, has become one of the best studied mud volcanoes. Those geological formations are characterized by the transport of large amounts of fluids, gas and mud from several kilometers beneath the seafloor. These materials are available for sampling at the seafloor surface - the HMMV is a window to the deep biosphere. A stationary installation as part of the LOOME project detected recent rapid mud discharges, thus rendering the HMMV an ideal location for studying how typical deep-sea microbes may colonize sedimentary material that (presumably) was little in contact with surface microbial life. The v4v6 hyper variable region of the 16S rRNA gene from 16 samples (Archaea and Bacteria) collected at the HMMV has been pyrosequenced as a contribution to the Census of Deep Life (CoDL). The read numbers varied with orders of magnitude between the sites (between 102 -104 ), from the periphery to the center. In the central area, there were very few reads detected, also the samples were very low in species richness and evenness (few species dominating) - the opposite of the old and abundant in reads areas in the hydrate zone and outside of the volcano (many more niches available - less extreme environment). Typical subsurface groups such as Crenarchaeota and Anaerolinecaeae were detected in the central area, and typical surface ones, ANME-3, Methylococcales and SRB in the others. These results confirmed and expanded previous microbial diversity studies on HMMV samples. NMDS plots showed separation of the microbes based on environmental dissimilarity, also providing insights on colonization and the time scales of its occurrence . Archaea and Bacteria followed similar patterns. These results have shed light on a very unique environment, and on a topic of global importance - the deep biosphere, and have underscored the need for even more exhaustive and innovative studies.