Methane Cycle in a Littoral Site of a Temperate Freshwater Lake

-Eutrophication of lakes results in the intensification of anaerobic processes, including methanogenesis, and therefore in enhanced emission of methane. A littoral area with its variable oxygen regime is the first to react to eutrophication. The diversity of microbial communities in littoral areas is insufficiently studied, and little data are available concerning the methane cycle microorganisms. In this work, the methanogenesis and methane oxidation were investigated in the littoral site of a freshwater temperate Lake Senezh (Russia). A combination of analytical, microbiological and molecular techniques was used, including physicochemical analyses, high-throughput sequencing, potential activity measurements, and cultivation on selective media. The littoral site was found to be an extremely labile ecological niche, which harbors a diverse community containing aerobic, facultative anaerobic and anaerobic microorganisms, both autotrophs and heterotrophs, which may perform all reactions of the N, S, and CH4 cycles. Methane formation was carried out via hydrogenotrophic, acetoclastic, methylotrophic, and methyl-reducing pathways. Among methanotrophs, type I organisms predominated; type II, nitrate- and nitrite-dependent methanotrophs were also revealed. Comparison of the average rates of methanogenesis and aerobic methane oxidation suggests that all methane, which may potentially be formed in the littoral site of the lake, could simultaneously be oxidized.

Automated summary

Eutrophication of lakes leads to increased methane emission, especially in littoral areas where the oxygen levels vary. The microbial communities in littoral areas, as well as the microorganisms involved in the methane cycle, are not well-studied. This study investigated methanogenesis and methane oxidation in a littoral site of Lake Senezh, Russia, using a combination of analytical, microbiological, and molecular techniques. The results revealed a diverse community of aerobic, facultative anaerobic, and anaerobic microorganisms capable of performing all reactions of the N, S, and CH4 cycles. Methane formation occurred through various pathways, and methane oxidation was predominantly carried out by type I methanotrophs, with type II nitrate- and nitrite-dependent methanotrophs also present. The study suggests that all potential methane formation in the littoral site of the lake could be simultaneously oxidized.