Microbial diversity in the deep sea and the underexplored “rare biosphere”

TLDR

Marine microbial evolution predicts that seawater communities contain far more taxa than the few thousand species currently catalogued, with an ancient rare biosphere that may be a vast source of genomic innovation. The study aims to demonstrate that bacterial communities in deep North Atlantic waters and diffuse hydrothermal vents are 10–100 times more diverse than previously reported. This was achieved by applying massively parallel tag sequencing to analyze microbial populations in these environments. The analyses revealed that a handful of dominant populations coexist with thousands of low‑abundance, highly divergent taxa that together constitute the majority of phylogenetic diversity and may have historically influenced planetary processes.

Abstract

The evolution of marine microbes over billions of years predicts that the composition of microbial communities should be much greater than the published estimates of a few thousand distinct kinds of microbes per liter of seawater. By adopting a massively parallel tag sequencing strategy, we show that bacterial communities of deep water masses of the North Atlantic and diffuse flow hydrothermal vents are one to two orders of magnitude more complex than previously reported for any microbial environment. A relatively small number of different populations dominate all samples, but thousands of low-abundance populations account for most of the observed phylogenetic diversity. This "rare biosphere" is very ancient and may represent a nearly inexhaustible source of genomic innovation. Members of the rare biosphere are highly divergent from each other and, at different times in earth's history, may have had a profound impact on shaping planetary processes.