As a CDEBI postdoctoral researcher I had the opportunity to analyze metagenomes
from Tonga Trench water and sediments. The motivation stemmed from the need to understand the microbial community composition and metabolic potential of the
deepest sites on Earth, oceanic trenches, for which little is known. Samples were
collected at 9100m water column depth. Metagenomes were prepped from water column depths of 400m, 3000m, 5000m and ~9100m, and sediment samples at 0, 1, and 2 meter below the seafloor (mbsf). The analysis of the sediment samples provided a new perspective of life in the deep ocean. The data for microbial community composition and metabolic profiles at 0 mbsf suggest that microbes are present and taxonomically similar to the deep water column microbes, and perform varied aerobic as well as anaerobic metabolisms, including degradation of organic carbon, oxidative phosphorylation, fermentation, nitrate reduction and sulfur oxidation. On the other hand, at 1 and 2 mbsf, the microbial community has diminished richness and diversity when compared to 0 mbsf and is potentially environmentally degraded due to rapid sedimentary deposition. The water samples varied from Archaea dominated at 400m, to over 90% Bacteria at 9000m. The 400m sample displays low oxygen metabolic signatures, while the mid water samples are the most similar to each other and possess aerobic metabolic signatures including archaeal ammonia oxidation. To our knowledge these are the deepest metagenomes analyzed to date, allowing for an unprecedented look of an understudied section of our planet.