Specificity of chloroform, 2-bromoethanesulfonate and fluoroacetate to inhibit methanogenesis and other anaerobic processes in anoxic rice field soil

Chloroform (CHCl3), 2-bromoethanesulfonate (BES) and fluoroacetate have frequently been used as methanogenic inhibitors in rice field soil and in other environments, but their effects on other microbial processes have not received sufficient attention. Therefore, we comparatively determined the effects of CHCl3, BES and fluoroacetate on different microbial processes in rice field soil slurry upon incubation under anoxic conditions: on the reduction of the electron acceptors nitrate, ferric iron, sulfate; on the production of CH4 and CO2; on the temporal change of the electron donors H2, acetate and propionate; and on the turnover of [2-14C]acetate during the early reduction phase (day 7), and during the later methanogenic phase (day 30). The results demonstrate: (1) fluoroacetate inhibited acetate consumption by all microorganisms, (2) BES generally inhibited CH4 production, and (3) CHCl3 not only inhibited methanogenesis, but partially also acetate-dependent sulfate reduction, and perhaps H2-dependent homoacetogenesis. The specificity of the different inhibitors resulted in characteristic patterns of the temporal change of electron donors and acceptors and of CH4. The pattern of propionate change was consistent with production by fermenting bacteria and consumption by sulfate reducers either using sulfate or methanogens as electron acceptor. Sulfate reducers were also found to be important for acetate consumption during the early phase of soil anoxia. Later on, however, methanogenic acetate consumption was much more pronounced. The application of inhibitors with different specificity was helpful for elucidating the flow of carbon and electrons during degradation of organic matter in anoxic rice field soil.