Lake Washington sediment enrichments. sediment metagenome

In this study, we addressed the role that provided nitrogen plays in determining the composition of methane-consuming communities and the methane oxidation potential in a well-studied model system. We applied a multi-phase approach combining microcosm enrichments and pure culture studies with methane oxidation potential measurements and high throughput sequencing. We focused on incubation conditions with a limited O2 availability as observed in the natural environment. 16S rRNA gene profiling showed that with N2 as the only available nitrogen source, communities were dominated by Methylomonas species as the major methane-oxidizing bacteria (MOB). In the presence of added nitrate however, Methylobacter species were the dominant MOB. Pure culture studies of Methylomonas and Methylobacter isolated from the same environment and incubated in the same way confirmed that the growth of a Methylomonas strain was not significantly affected when N2 was the only provided nitrogen source, while growth of a Methylobacter strain was negatively impacted. By further exposing long-term methane fed microbial communities to different nitrogen sources, intraspecific dynamics of non-methanotrophic community members were observed, suggesting nitrate as an additional selective factor for co-occurring species. Our results show that provided nitrogen source is an important factor determining specific responses of individual community members and consequently affecting community composition and overall methane consumption.