The bacterial sulfur cycle in expanding dysoxic and euxinic marine waters.

Daan M Van Vliet,Bas E Dutilh,Jaap S Sinninghe Damsté,Irene Sánchez-Andrea,Alfons J M Stams,Laura Villanueva,F.A Bastiaan Von Meijenfeldt

doi:10.1111/1462-2920.15265

Abstract

Dysoxic marine waters (DMW, < 1 μM oxygen) are currently expanding in volume in the oceans, which has biogeochemical, ecological and societal consequences on a global scale. In these environments, distinct bacteria drive an active sulfur cycle, which has only recently been recognized for open‐ocean DMW. This review summarizes the current knowledge on these sulfur‐cycling bacteria. Critical bottlenecks and questions for future research are specifically addressed. Sulfate‐reducing bacteria (SRB) are core members of DMW. However, their roles are not entirely clear, and they remain largely uncultured. We found support for their remarkable diversity and taxonomic novelty by mining metagenome‐assembled genomes from the Black Sea as model ecosystem. We highlight recent insights into the metabolism of key sulfur‐oxidizing SUP05 and Sulfurimonas bacteria, and discuss the probable involvement of uncultivated SAR324 and BS‐GSO2 bacteria in sulfur oxidation. Uncultivated Marinimicrobia bacteria with a presumed organoheterotrophic metabolism are abundant in DMW. Like SRB, they may use specific molybdoenzymes to conserve energy from the oxidation, reduction or disproportionation of sulfur cycle intermediates such as S0 and thiosulfate, produced from the oxidation of sulfide. We expect that tailored sampling methods and a renewed focus on cultivation will yield deeper insight into sulfur‐cycling bacteria in DMW.

Highlights

Oxygen deficiency is a rather common phenomenon in marine waters caused by microbial aerobic respiration coupled to the degradation of organic matter, combined with insufficient supply of oxygen through water circulation or diffusion (Canfield et al, 2005)
The largest Oxygen-minimum zones (OMZs) are found in the Eastern Tropical North Pacific (ETNP), the Eastern Tropical South Pacific (ETSP) and the Arabian Sea (Fig. 1, Table S1)
Based on 16S rRNA gene surveys, specific gammaproteobacterial bacteria belonging to the SUP05 clade and closely related to known sulfur-oxidizing symbionts have been identified as abundant putative sulfur-oxidizing bacteria (SOB) in DMW

Summary

Introduction

Oxygen deficiency is a rather common phenomenon in marine waters caused by microbial aerobic respiration coupled to the degradation of organic matter, combined with insufficient supply of oxygen through water circulation or diffusion (Canfield et al, 2005). We mined metagenome data to obtain 13 MAGs of putative SRB from the Black Sea, encoding complete or incomplete reductive Dsr pathways (Figs 3A, B and 5, Table S2, Supporting Information Methods).

Results

Conclusion