Theoretical estimates of equilibrium carbon and hydrogen isotope effects in microbial methane production and anaerobic oxidation of methane

Microbial production and consumption of methane are widespread in natural artificial environments, with important economic climatic implications. Attempts to use the isotopic composition identify its sources complicated by incomplete understanding mechanisms variation methane’s composition. Knowledge equilibrium isotope fractionations among large organic intracellular intermediates microbial pathways must form basis any exploration variation, but estimates these currently unavailable. To address this gap, we calculated fractionation carbon (13C/12C) hydrogen (D/H) isotopes compounds anaerobic metabolisms, as well abundance double substitutions (“clumping,” i.e., a single 13C–D bond or two 12C–D bonds) compounds. The factors were using density functional theory at M06-L/def2-TZVP level SMD implicit solvation model, which recently tested against measured fractionations. computed 13? 2? values decrease decreasing oxidation state atom molecules, resulting preference for enrichment 13C D molecules more oxidized carbon. Using ? values, prominent methanogenesis (hydrogenotrophic, methylotrophic acetoclastic) pathway (AOM) over temperature range 0–700 °C. Our compare favorably experimental constraints, where available, then used investigate relation between apparent during AOM thermodynamic drive reactions. We show that detailed map along metabolic allows an evaluation contribution kinetic effects observed laboratory, settings. comprehensive set study provides firm future explorations metabolism.