Enrichment and genomic characterization of a N 2 O-reducing chemolithoautotroph from a deep-sea hydrothermal vent

Abstract

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.