The development of methane clumped Isotopologues as a tool in tracing microbial methane sources and sinks

Methane (CH4) is an important energy source, a potent greenhouse gas, and a potential biosignature in extraterrestrial environments. Quantifying the sources and sinks of CH4 through isotopic analysis is crucial to calculating the methane budget on both Earth and other planetary bodies. To date, this has remained a challenge, due to the non-unique signatures given by the traditional ‘bulk’ isotope signatures (ẟ13C and ẟD). Tools to measure the distributions of doubly-substituted (a.k.a. ‘clumped’) isotopologues of methane (∆13CH3D and ∆12CH2D2) have been developed and applied in the last decade to track methane sources and sinks. The clumped isotope signatures of methane related to microbial processes (microbial methanogenesis and oxidation) have been extensively studied, but the controlling factors of the clumped isotopologues fractionations of microbial methane are still poorly understood. This talk focuses on the research projects I have been working on, with the aim to resolve some controlling factors on both microbial methanogenesis and methane oxidation. The first project is a compilation of ∆13CH3D and ∆12CH2D2 data in various methanogenesis pathways, including hydrogenotrophic, methylotrophic, acetotrophic, and methoxydotrophic methanogenesis. We found pathway-dependent isotope fractionation in different methanogenesis processes, characterized by the exogenous combinatorial effect in methylotrophic methanogenesis versus endogenous combinatorial effect in hydrogenotrophic methanogenesis. The second project is the clumped isotope signatures in a closed-system microbial aerobic methane oxidation, where the cross-membrane methane transport limitation caused deviation from the canonical Rayleigh fractionation. My work expands the available isotopic data on microbial methanotrophy and methanogenesis, and contributes to the development of clumped isotopes as a tool to better estimate methane sources and sinks across the Earth, and beyond.