Fig. P1.

Stoichiometry and fluxes during the AOM with sulfate by marine microbial consortia. The mode of coupling between methane oxidation and sulfate reduction is insufficiently understood. AOM has one of the lowest energy yields among reactions that fuel microbial life in natural habitats. The enzymatic reactions in AOM must, therefore, operate not far from equilibrium, favoring product back flux. This finding is illustrated (Lower) by means of reaction vectors (⇀, forward flux; ↽, back flux; →, sum or net reaction; lengths indicate rates, the figure is not drawn with proportionality, and exact values are shown). The net rates (v; same for carbon and sulfur because of stoichiometry) are composed of forward and back fluxes (respective symbols: f_+C, f_−C for carbon and f_+S, f_−S for sulfur). In contrast to the net rates of methane oxidation and sulfate reduction, the respective forward and back fluxes can be independent of each other.