16S rRNA gene amplicon sequencing of the hypolimnion of a methane-rich freshwater lake

Aerobic methanotrophs are bacteria that limit methane emissions from natural sources, oxidizing methane to produce biomass and capture energy. These bacteria can form syntrophies with nonmethanotrophic methylotrophs, transferring to them some of the carbon captured via aerobic methane oxidation (MOx). This syntrophy has been observed to increase the MOx rate in co-culture, so understanding how it plays out in natural settings is critical to fully understanding the global methane cycle. To that end, we examined how natural methane-oxidizing communities correlate with environmental conditions in a methane-rich freshwater lake in situ. We determined the microbial compositions of each sample using 16S rRNA gene amplicon sequencing and measured the corresponding methane concentrations, oxygen concentrations, temperature, and in situ first-order rate constants of MOx. We then assessed 1) which families correlate with the first-order rate constant of MOx, 2) how the abiotic factors of oxygen, methane, and temperature affect the populations of both aerobic methanotrophs and nonmethanotrophic methylotrophs, 3) how the populations of aerobic methanotrophs and nonmethanotrophic methylotrophs change during a typical MOx determination experiment, and 4) if the addition of external nitrogen or carbon sources can disrupt any observed syntrophy.