Clumped isotopes as fingerprints of microbial methane production pathways in marine sediments

Abstract

Microbial methanogenesis in marine sediments produces significant amounts of methane from various substrates; however, identifying the active pathways in situ remains challenging. While the bulk and clumped isotopic signatures of methane from different pathways have been studied in pure cultures, these are difficult to compare with complex natural settings. Previously, we linked clumped isotope signatures to the methanogenic pathway in marine sediment incubations with complete substrate conversion. Here, we investigated the temporal kinetics of microbial methane formation. Sediments were incubated with hydrogen, methanol and acetate to monitor the temporal evolution of bulk and clumped methane isotopic signatures and changes in the methanogenic community. The isotopic composition of methane exhibited a clear, substrate-specific temporal evolution, correlating with the expected methanogenic taxa enriched by each substrate. Our results contribute to understanding the kinetics and isotopic signatures of different methanogenic processes, supporting bottom-up estimations of methane emission sources from various natural environments with diverse methanogenic communities.