Network analysis of 16S rRNA sequences suggests microbial keystone taxa contribute to marine N 2 O cycling.

The mechanisms by which large-scale microbial community function emerges from complex ecological interactions between individual taxa and functional groups remain obscure. We leveraged network analyses of 16S rRNA amplicon sequences obtained over a seven-month timeseries in seasonally anoxic Saanich Inlet (Vancouver Island, Canada) to investigate relationships between microbial community structure and water column N 2 O cycling. Taxa separately broadly into three discrete subnetworks with contrasting environmental distributions. Oxycline subnetworks were structured around keystone aerobic heterotrophs that correlated with nitrification rates and N 2 O supersaturations, linking N 2 O production and accumulation to taxa involved in organic matter remineralization. Keystone taxa implicated in anaerobic carbon, nitrogen, and sulfur cycling in anoxic environments clustered together in a low-oxygen subnetwork that correlated positively with nitrification N 2 O yields and N 2 O production from denitrification. Close coupling between N 2 O producers and consumers in the anoxic basin is indicated by strong correlations between the low-oxygen subnetwork, PICRUSt2-predicted nitrous oxide reductase (nosZ) gene abundances, and N 2 O undersaturation. This study implicates keystone taxa affiliated with common ODZ groups as a potential control on water column N 2 O cycling and provides a theoretical basis for further investigations into marine microbial interaction networks.