Hydrogen and carbon isotope fractionation during experimental production of bacterial methane

This paper presents C and H isotope compositions of compounds involved in methane production by pure cultures of Methanobacterium formicicum. The C isotope compositions of the methane produced and of the residual CO 2 are compared to data observed in natural conditions in marine sediments. This comparison leads to further evidence that CO 2 reduction is an important mechanism for microbial generation of methane in deep marine sediments. The H isotope compositions show involvment of the water hydrogen into methane as well as hydrogen exchange between water and molecular hydrogen in the course of CO 2 reduction. A mechanism is proposed as a possible explanation for the data obtained involving conjugated reactions of CO 2-reduction and enzymatic reduction of water.