title: SAR11 bacteria linked to ocean anoxia and nitrogen loss.
abstract: 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 N2 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.
authors.forename: Despina
authors.initials: D
authors.lastname: Tsementzi
authors.forename: Jieying
authors.initials: J
authors.lastname: Wu
authors.forename: Samuel
authors.initials: S
authors.lastname: Deutsch
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Nath
authors.forename: Luis M
authors.initials: LM
authors.lastname: Rodriguez-R
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Burns
authors.forename: Piyush
authors.initials: P
authors.lastname: Ranjan
authors.forename: Neha
authors.initials: N
authors.lastname: Sarode
authors.forename: Rex R
authors.initials: RR
authors.lastname: Malmstrom
authors.forename: Cory C
authors.initials: CC
authors.lastname: Padilla
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Stone
authors.forename: Laura A
authors.initials: LA
authors.lastname: Bristow
authors.forename: Morten
authors.initials: M
authors.lastname: Larsen
authors.forename: Jennifer B
authors.initials: JB
authors.lastname: Glass
authors.forename: Bo
authors.initials: B
authors.lastname: Thamdrup
authors.forename: Tanja
authors.initials: T
authors.lastname: Woyke
authors.forename: Konstantinos T
authors.initials: KT
authors.lastname: Konstantinidis
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Stewart
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D020561:Alphaproteobacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000693:Anaerobiosis / Q000235:genetics; D059001:Aquatic Organisms / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D058440:Denitrification; D020869:Gene Expression Profiling; D005798:Genes, Bacterial; D016680:Genome, Bacterial / Q000235:genetics; D009565:Nitrate Reductases / Q000235:genetics / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009792:Oceans and Seas; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis* / Q000378:metabolism; D010802:Phylogeny; D012623:Seawater / Q000737:chemistry*; D059010:Single-Cell Analysis; D014158:Transcription, Genetic
chemical_list: D009566:Nitrates; D009573:Nitrites; D009565:Nitrate Reductases; D009584:Nitrogen; D010100:Oxygen