Diversity and Biogeography of Bathyal and Abyssal Seafloor Bacteria.

Alban Ramette,Antje Boetius,Christina A Kellogg,Lucie Zinger,Christina Bienhold

doi:10.1371/journal.pone.0148016

Abstract

The deep ocean floor covers more than 60% of the Earth’s surface, and hosts diverse bacterial communities with important functions in carbon and nutrient cycles. The identification of key bacterial members remains a challenge and their patterns of distribution in seafloor sediment yet remain poorly described. Previous studies were either regionally restricted or included few deep-sea sediments, and did not specifically test biogeographic patterns across the vast oligotrophic bathyal and abyssal seafloor. Here we define the composition of this deep seafloor microbiome by describing those bacterial operational taxonomic units (OTU) that are specifically associated with deep-sea surface sediments at water depths ranging from 1000–5300 m. We show that the microbiome of the surface seafloor is distinct from the subsurface seafloor. The cosmopolitan bacterial OTU were affiliated with the clades JTB255 (class Gammaproteobacteria, order Xanthomonadales) and OM1 (Actinobacteria, order Acidimicrobiales), comprising 21% and 7% of their respective clades, and about 1% of all sequences in the study. Overall, few sequence-abundant bacterial types were globally dispersed and displayed positive range-abundance relationships. Most bacterial populations were rare and exhibited a high degree of endemism, explaining the substantial differences in community composition observed over large spatial scales. Despite the relative physicochemical uniformity of deep-sea sediments, we identified indicators of productivity regimes, especially sediment organic matter content, as factors significantly associated with changes in bacterial community structure across the globe.

Highlights

The deep ocean floor comprising the lower continental margin and abyssal plains at >1000 m water depth covers about half of Earth’s surface
Accumulation curves (S3 Fig) indicated that at coarse taxonomic resolution, the diversity of most taxa was captured with this global sample set, but a considerable part of the global bacterial diversity in deep-sea sediments at the OTU0.03 level was still missing
By investigating the composition and distribution of benthic deep-sea bacterial communities at the global scale, we show that bacterial communities of deep-sea surface sediments are distinct from those of the pelagic or the subsurface seafloor biosphere, and this already at the class level

Summary

Introduction

The deep ocean floor comprising the lower continental margin and abyssal plains at >1000 m water depth covers about half of Earth’s surface. Deep-sea surface sediments of the top 2 cm consist mostly of clay minerals, shells of planktonic organisms and organic matter; the benthic communities inhabiting the deep-sea floor are dominated by bacteria in terms of total. Sloan Foundation) to AB and AR, the Helmholtz Association and the Max Planck Society. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Methods

Results

Conclusion