Abstract
The soil microbial communities in two Japanese paddy fields were compared: site PA, which emits methane at the domestic average level, and site PX, which emits more than five times that amount. The transcription levels of methyl-coenzyme M reductase (mcrA) significantly increased during peak methane emissions at site PX, but not at site PA. The anaerobic methanotroph "Candidatus Methanoperedens" exhibited low activity and abundance exclusively at site PX. The genus Methanoregula was the most active methanogen at both sites; however, the dominant methanotrophs differed, with Methylocystis dominating at site PA and Methylomonas at site PX.