Aerobic methane production in oxygenated water column of lake ecosystems

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We conducted the field and laboratory studies to identify the aerobic methane production pathways in lake ecosystems. The field studies revealed that dissolved CH4 concentrations often exhibit a subsurface maximum during the stratified period in many lakes. In particular, large, oligotrophic lakes tended to form large CH4 maximum. Moreover, seasonal occurrence of the CH4 maximum was closely related to the abundance of planktonic microbes (Synechococcus), suggesting CH4 production by microbes even in the presence of O2. Furthermore, the microcosm experiments showed the aerobic CH4 production when methylphosphonic acid (MPn) was added to the P-deficient lake water, suggesting the expression of a carbon-phosphorus lyase for P utilization and producing CH4 from MPn. The present study revealed the causal relationships between aerobic microorganisms, their phosphonate metabolism, and CH4 production, which clarify the novel methane production pathway observed in many oligotrophic lakes.