Comparisons of Microbial Life in the Kermadec and Mariana Trenches

Hadal trenches, oceanic locations deeper than 6,000 m, are thought to have distinct microbial communities compared to those at shallower depths due to high hydrostatic pressures,topographical funneling of organic matter, and biogeographical isolation. In this presentation I will discuss the relationships among hadal microbial communities in the Mariana and Kermadec trenches, which are separated by more than 6,000 km. In the case of water column samples estimates of microbial protein production indicate active populations under in situ hydrostatic pressures and increasing adaptation to pressure with depth. Analyses of 16S rRNA gene Illumina tag sequence indicate that depth, trench of collection, and size fraction are important drivers of microbial community structure. Curiously most of the differences between the two trench microbiomes consists of taxa whose distributions are not specific to hadal depths and extend throughout the water column. Sediment consortia were also distinct between trenches, with higher relative sequence abundances of taxa implicated in organic matter degradation present in the more organic rich Kermadec Trench. The Mariana Trench, and deeper sediments in both trenches, were enriched in taxa predicted to break down recalcitrant material and novel lineages. The most sequence-abundant taxa were not trench-specific and were related to those found in other hadal and abyssal habitats. Binned metagenomes derived from hadal sediments indicate the presence of closely related sediment genomes between trenches, but with endemism evident at the strain level.