Methanotrophic bacteria in cold seeps of the floodplains of northern rivers

Small mud volcanoes (cold seeps), which are common in the floodplains of northern rivers, are potentially important (although poorly studied) sources of atmospheric methane. Field research on the cold seeps of the Mukhrina River (Khanty-Mansiysk Autonomous okrug, Russia) revealed methane fluxes from these structures to be orders of magnitude higher than from equivalent areas of the mid-taiga bogs. Microbial communities developing around the seeps were formed under conditions of high methane concentrations, low temperatures (3–5°C), and near-neutral pH. Molecular identification of methane-oxidizing bacteria from this community by analysis of the pmoA gene encoding particulate methane monooxygenase revealed both type I and type II methanotrophs (classes Gammaproteobacteria and Alphaproteobacteria, respectively), with prevalence of type I methanotrophs. Among the latter, microorganisms related to Methylobacter psychrophilus and Methylobacter tundripaludum, Crenothrix polyspora (a stagnant water dweller), and a number of methanotrophs belonging to unknown taxa were detected. Growth characteristics of two methanotrophic isolates were determined. Methylobacter sp. CMS7 exhibited active growth at 4–10°C, while Methylocystis sp. SB12 grew better at 20°C. Experimental results confirmed the major role of methanotrophic gammaproteobacteria in controlling the methane emission from cold river seeps.