Abstract
Nitrous oxide (N2O) is a greenhouse gas and also leads to stratospheric ozone depletion. In natural environments, only a single N2O sink process is the microbial reduction of N2O to N2, which is mediated by nitrous oxide reductase (NosZ) encoded by nosZ gene. The nosZ phylogeny has two distinct clades, clade I and formerly overlooked clade II. In deep-sea hydrothermal environments, several members of the class Campylobacteria are shown to harbor clade II nosZ gene and perform the complete denitrification of nitrate to N2; however, little is known about their ability to grow on exogenous N2O as the sole electron acceptor. Here, we obtained an enrichment culture from a deep-sea hydrothermal vent in the Southern Mariana Trough, which showed a respiratory N2O reduction with H2 as an electron donor. The single amplicon sequence variant (ASV) presenting 90% similarity to Hydrogenimonas species within the class Campylobacteria was predominant throughout the cultivation period. Metagenomic analyses using a combination of short-read and long-read sequence data succeeded in reconstructing a complete genome of the dominant ASV, which encoded clade II nosZ gene. This study represents the first cultivation analysis that shows the occurrence of N2O-respiring microorganisms in a deep-sea hydrothermal vent and provides the opportunity to assess their capability to reduce N2O emission from the environments.
Highlights
Nitrous oxide (N2O) is a stable greenhouse gas and a major stratospheric ozone layer-depleting substance of the 21th century (Ravishankara et al, 2009)
The abundance of microorganisms possessing the clade II NosZ outnumbers that of microorganisms possessing the clade I NosZ in the diverse environments (Jones et al, 2013, 2014), and clade II organisms have been reported with the higher affinity to N2O than clade I organisms (Yoon et al, 2016), suggesting that microorganisms possessing the clade II NosZ play a crucial role in attenuating N2O emission in the various natural environments
Dereplicate 421,406 Illumina reads resulted in 11 bacterial amplicon sequence variant (ASV)
Summary
Nitrous oxide (N2O) is a stable greenhouse gas and a major stratospheric ozone layer-depleting substance of the 21th century (Ravishankara et al, 2009). Nitrous oxide (N2O) can be reduced at the final step of the microbial denitrification pathway, which consists of the sequential reduction of NO−3 to NO−2 , NO, N2O, and N2. Described clade II NosZ (Sanford et al, 2012; Jones et al, 2013) is often identified within non-denitrifying N2O-reducing microorganisms that lack other denitrification genes or perform dissimilatory nitrate reduction to ammonium. The abundance of microorganisms possessing the clade II NosZ outnumbers that of microorganisms possessing the clade I NosZ in the diverse environments (Jones et al, 2013, 2014), and clade II organisms have been reported with the higher affinity to N2O than clade I organisms (Yoon et al, 2016), suggesting that microorganisms possessing the clade II NosZ play a crucial role in attenuating N2O emission in the various natural environments
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