title: Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27.
abstract: N2O-reducing organisms with nitrous oxide reductases (NosZ) are known as the only biological sink of N2O in the environment. Among the most abundantnosZgenes found in the environment arenosZgenes affiliated with the understudiedGemmatimonadetesphylum. In this study, a unique regulatory mechanism of N2O reduction inGemmatimonas aurantiacastrain T-27, an isolate affiliated with theGemmatimonadetesphylum, was examined. Strain T-27 was incubated with N2O and/or O2as the electron acceptor. Significant N2O reduction was observed only when O2was initially present. When batch cultures of strain T-27 were amended with O2and N2O, N2O reduction commenced after O2was depleted. In a long-term incubation with the addition of N2O upon depletion, the N2O reduction rate decreased over time and came to an eventual stop. Spiking of the culture with O2resulted in the resuscitation of N2O reduction activity, supporting the hypothesis that N2O reduction by strain T-27 required the transient presence of O2The highest level ofnosZtranscription (8.97nosZtranscripts/recAtranscript) was observed immediately after O2depletion, and transcription decreased ∼25-fold within 85 h, supporting the observed phenotype. The observed difference between responses of strain T-27 cultures amended with and without N2O to O2starvation suggested that N2O helped sustain the viability of strain T-27 during temporary anoxia, although N2O reduction was not coupled to growth. The findings in this study suggest that obligate aerobic microorganisms withnosZgenes may utilize N2O as a temporary surrogate for O2to survive periodic anoxia.IMPORTANCEEmission of N2O, a potent greenhouse gas and ozone depletion agent, from the soil environment is largely determined by microbial sources and sinks. N2O reduction by organisms with N2O reductases (NosZ) is the only known biological sink of N2O at environmentally relevant concentrations (up to ∼1,000 parts per million by volume [ppmv]). Although a large fraction ofnosZgenes recovered from soil is affiliated withnosZfound in the genomes of the obligate aerobic phylumGemmatimonadetes, N2O reduction has not yet been confirmed in any of these organisms. This study demonstrates that N2O is reduced by an obligate aerobic bacterium,Gemmatimonas aurantiacastrain T-27, and suggests a novel regulation mechanism for N2O reduction in this organism, which may also be applicable to other obligate aerobic organisms possessingnosZgenes. We expect that these findings will significantly advance the understanding of N2O dynamics in environments with frequent transitions between oxic and anoxic conditions.
authors.affiliation: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.
authors.forename: Doyoung
authors.initials: D
authors.lastname: Park
authors.affiliation: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.
authors.forename: Hayeon
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, South Korea syoon80@kaist.ac.kr.
authors.forename: Sukhwan
authors.initials: S
authors.lastname: Yoon
mesh_terms: D001420:Bacteria, Aerobic / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D009609:Nitrous Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D010088:Oxidoreductases; C022763:nitrous oxide reductase; D009609:Nitrous Oxide; D010100:Oxygen
keywords: Gemmatimonadetes; RT-qPCR; nitrous oxide; nitrous oxide reduction