Co-cultivation of the strictly anaerobic methanogen Methanosarcina barkeri with aerobic methanotrophs in an oxygen-limited membrane bioreactor.

Wetlands contribute to 30% of global methane emissions due to an imbalance between microbial methane production and consumption. Methanogenesis and methanotrophy have mainly been studied separately, and little is known about their potential interactions in aquatic environments. To mimic the interaction between methane producers and oxidizers in the environment, we co-cultivated the methanogenic archaeon Methanosarcina barkeri with aerobic Methylocystaceae methanotrophs in an oxygen-limited bioreactor using acetate as methanogenic substrate. Methane, acetate, dissolved oxygen, available nitrogen, pH, temperature, and cell density were monitored to follow system stability and activity. Stable reactor operation was achieved for two consecutive periods of 2 months. Fluorescence in situ hybridization micrographs indicated close association between both groups of microorganisms. This association suggests that the methanotrophs profit from direct access to the methane that is produced from acetate, while methanogens are protected by the concomitant oxygen consumption of the methanotrophs. This proof of principle study can be used to set up systems to study their responses to environmental changes.