Composition of aquatic microbial communities and their relation to water-column methane cycling among Mackenzie Delta lakes, western Canadian Arctic

Seasonal dynamics of water-column microbial communities and methanotrophs were monitored in six lakes of the Mackenzie River Delta using gene sequencing of 16S rRNA gene and qPCR of the 16S rRNA and methane monooxygenase (pmoA) genes. Selected lakes varied in biogeochemistry based on annual river-to-lake connection times, which we hypothesized would impact bacterial community composition and methanotroph relative abundance. River-to-lake and seasonal influences on carbon bioavailability and quantity, nutrients, temperature and flooding correlated with seasonal changes in microbial composition. Methanotroph groups including Methylobacter and methylotrophs Candidatus Methylopumilus and Candidatus Methylophilaceae were detected in all lakes but at higher relative abundance in the winter and spring when lake-water methane concentrations were highest. Open-water methanotroph abundance was highest in spring. In experimental enclosures, methanogenesis was detected in oxygenated lake-water and rates varied by lake type. Nutrient enhancements altered microbial composition and increased rates of methane oxidation with increasing lake isolation.