Effect of inhibition of acetoclastic methanogenesis on growth of archaeal populations in an anoxic model environment

Methyl fluoride is frequently used to specifically inhibit acetoclastic methanogenesis, thus allowing deter-mination of the relative contribution of acetate versus H2/CO2 to total CH4 production in natural environ-ments. However, the effect of the inhibitor on growth of the target archaeal population has not yet been studied. Therefore, we incubated rice roots as an environmental model system under anoxic conditions in the presence and absence of CH3F, measured the activity and Gibbs free energy (G) of CH4 production, and determined the abundance of individual archaeal populations by using a combination of quantitative (real-time) PCR and analysis of terminal restriction fragment length polymorphism targeting the 16S rRNA gene. It was shown that CH3F specifically inhibited not only acetoclastic methanogenic activity but also the proliferation of Methano-sarcina spp, which were the prevalent acetoclastic methanogens in our environmental model system. Therefore, inhibition experiments with CH3F seem to be a suitable method for quantifying acetoclastic CH4 production. It is furthermore shown that the growth and final population size of methanogens were consistent with energetic conditions that at least covered the maintenance requirements of the population. Atmospheric CH4 significantly contributes to global warm-ing (4, 35). Among the dominant sources of CH4 are wetlands and flooded rice fields, which are responsible for a third of th