The deep ocean is one of the more elusive environments on the planet, and yet one of the most important in terms of understanding the intricate biogeochemical cycles and oceanographic patterns shaping our world.

It is an environment that takes up the greatest fraction of the ocean at depths greater than 200m and harbors an estimated 55% of all prokaryotes in aquatic habitats. The deep ocean is characteristically dark, cold, and food-limited, with high hydrostatic pressure as the most unique physical parameter.

It has been hypothesized that the evolution of autochthonous deep-sea microbes has been significantly affected by hydrostatic pressure at depths greater than 2,000 m. Piezophilic (“pressure-loving”) microorganisms harbor unique adaptations to cope with deep-sea high pressure conditions. Cultivation efforts have thus far only yielded piezophilic isolates from a narrow phylogenetic grouping.

In recent years to tools of Illumina tag sequencing, environmental genomics and single-cell genomics has begun to reveal a new world of microbial life in this portion of the dark biosphere.  This suggests that it is extremely important to study this distant habitat to obtain a complete view of the Earth microbiome.