Modulation of methyl-coenzyme M reductase expression alters the isotopic composition of microbial methane.

The stable isotopic composition of microbial methane varies substantially, and the underlying causes are debated. In this work, we experimentally controlled the abundance of the central enzyme in methanogenesis, methyl-coenzyme M reductase (MCR), in and tested whether its cellular concentration alters methane isotopic compositions. We found that during growth on methanol and acetate, lowering the expression of increases the degree of hydrogen isotope exchange between methane and water.

Controls on the isotopic composition of microbial methane.

Microbial methane production (methanogenesis) is responsible for more than half of the annual emissions of this major greenhouse gas to the atmosphere. Although the stable isotopic composition of methane is often used to characterize its sources and sinks, strictly empirical descriptions of the isotopic signature of methanogenesis currently limit these attempts. We developed a metabolic-isotopic model of methanogenesis by carbon dioxide reduction, which predicts carbon and hydrogen isotopic fractionations, and clumped isotopologue distributions, as functions of the cell's environment.

Sulfate-dependent reversibility of intracellular reactions explains the opposing isotope effects in the anaerobic oxidation of methane.

The anaerobic oxidation of methane (AOM) is performed by methanotrophic archaea (ANME) in distinct sulfate-methane interfaces of marine sediments. In these interfaces, AOM often appears to deplete methane in the heavy isotopes toward isotopic compositions similar to methanogenesis. Here, we shed light on this effect and its physiological underpinnings using a thermophilic ANME-1-dominated culture.

Cost-effective density functional theory (DFT) calculations of equilibrium isotopic fractionation in large organic molecules.

The application of stable isotopes to address a wide range of biochemical, microbiological and environmental problems is hindered by the experimental difficulty and the computational cost of determining equilibrium isotopic fractionations (EIF) of large organic molecules. Here, we evaluate the factors that impact the accuracy of computed EIFs and develop a framework for cost-effective and accurate computation of EIFs by density functional theory (DFT). We generated two benchmark databases of experimentally determined EIFs, one for H isotopes and another for the isotopes of the heavy atoms C, N and O.