Lipid biomarkers reveal dominance of aerobic methanotrophy in a continental serpentinizing system

Sources and sinks of methane within an advanced serpentinization-influenced system were investigated at the Coast Range Ophiolite Microbial Observatory (CROMO) in Lower Lake, California. Subsurface water-rock reactions at CROMO contribute to unique, high pH groundwaters and substantial methane emissions. We performed lipid analysis on biomass and measured radiocarbon and stable carbon isotopic composition of groundwater to trace the origins and fate of methane. Specific groups of microorganisms involved in methane cycling were identified through analysis of membrane lipid components. Aerobic methanotrophs dominated the samples, with evidence of heterotrophic bacteria but no detection of anaerobic methanotrophy or methanogens. Following these data, microbial activity may be a significant sink but not a major source of methane at this site.