Journal Article

SAR11 bacteria linked to ocean anoxia and nitrogen loss

Thamdrup, Bo, Woyke, Tanja, Bristow, Laura A., Ranjan, Piyush, Deutsch, Samuel, Larsen, Morten, Burns, Andrew S., Stone, Benjamin K., Konstantinidis, Konstantinos T., Wu, Jieying, Nath, Sangeeta, Stewart, Frank J., Padilla, Cory C., Tsementzi, Despina, Sarode, Neha, Glass, Jennifer B., Malmstrom, Rex R., Rodriguez-R, Luis M.

2016

Overview

Bacteria of the SAR11 clade constitute up to one half of all microbial cells in the oxygen-rich surface ocean. SAR11 bacteria are also abundant in oxygen minimum zones (OMZs), where oxygen falls below detection and anaerobic microbes have vital roles in converting bioavailable nitrogen to N 2 gas. Anaerobic metabolism has not yet been observed in SAR11, and it remains unknown how these bacteria contribute to OMZ biogeochemical cycling. Here, genomic analysis of single cells from the world’s largest OMZ revealed previously uncharacterized SAR11 lineages with adaptations for life without oxygen, including genes for respiratory nitrate reductases (Nar). SAR11 nar genes were experimentally verified to encode proteins catalysing the nitrite-producing first step of denitrification and constituted ~40% of OMZ nar transcripts, with transcription peaking in the anoxic zone of maximum nitrate reduction activity. These results link SAR11 to pathways of ocean nitrogen loss, redefining the ecological niche of Earth’s most abundant organismal group. Bacteria of the SAR11 clade constitute up to one half of all marine microbes and are thought to require oxygen for growth; here, a subgroup of SAR11 bacteria are shown to thrive in ocean oxygen minimum zones and to encode abundant respiratory nitrate reductases. An anoxic niche for SAR11 bacteria SAR11 bacteria, the most abundant type of microbe in the world's oceans, are thought to require oxygen for growth, yet they are also abundant in waters where oxygen levels are low. Frank Stewart and colleagues show here that a subgroup of SAR11 bacteria that thrives in ocean oxygen minimum zones have adapted to the microaerobic/anaerobic conditions there, and they encode abundant respiratory nitrate reductases that perform the first step in denitrification. These results redefine the ecological niche of Earth's most abundant organismal group and suggest that they are substantial contributors to nitrogen loss in oxygen minimum zones.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 38/43 / 38/44 / 38/47 / 631/326/171/1878 / 631/326/47/4112 / 704/829/826 / 82/80 / Adaptation, Physiological - genetics / Alphaproteobacteria - classification / Alphaproteobacteria - genetics / Alphaproteobacteria - isolation & purification / Alphaproteobacteria - metabolism / Anaerobiosis - genetics / Aquatic Organisms - enzymology / Aquatic Organisms - genetics / Aquatic Organisms - isolation & purification / Aquatic Organisms - metabolism / BASIC BIOLOGICAL SCIENCES / Denitrification / Ecological research / Element cycles / Environmental aspects / ENVIRONMENTAL SCIENCES / Gene Expression Profiling / Genes, Bacterial / Genome, Bacterial - genetics / Humanities and Social Sciences / Hypoxia (Aquatic ecology) / Marine biology / multidisciplinary / Nitrate Reductases - genetics / Nitrate Reductases - metabolism / Nitrates - metabolism / Nitrites - metabolism / Nitrogen - analysis / Nitrogen - metabolism / Oceans and Seas / Oxidation-Reduction / Oxygen - analysis / Oxygen - metabolism / Phylogeny / Proteobacteria / Science / Seawater - chemistry / Single-Cell Analysis / Transcription, Genetic / Water microbiology