Enrichment and Genomic Characterization of a N(2)O-Reducing Chemolithoautotroph From a Deep-Sea Hydrothermal Vent

Nitrous oxide (N(2)O) is a greenhouse gas and also leads to stratospheric ozone depletion. In natural environments, only a single N(2)O sink process is the microbial reduction of N(2)O to N(2), 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 N(2); however, little is known about their ability to grow on exogenous N(2)O 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 N(2)O reduction with H(2) 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 N(2)O-respiring microorganisms in a deep-sea hydrothermal vent and provides the opportunity to assess their capability to reduce N(2)O emission from the environments.