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 fre quently been used as methanogenic inhibitors in rice field soil and in othe r environments, but their effects on other microbial processes have not rec eived sufficient attention. Therefore, we comparatively determined the effe cts of CHCl3, BES and fluoroacetate on different microbial processes in ric e field soil slurry upon incubation under anoxic conditions: on the reducti on of the electron accepters nitrate, ferric iron, sulfate; on the producti on of CH4 and CO2; on the temporal change of the electron donors H-2, aceta te and propionate; and on the turnover of [2-C-14]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) CH Cl3 not only inhibited methanogenesis, but partially also acetate-dependent sulfate reduction, and perhaps H-2-dependent homoacetogenesis. The specifi city of the different inhibitors resulted in characteristic patterns of the temporal change of electron donors and accepters and of CH4. The pattern o f propionate change was consistent with production by fermenting bacteria a nd consumption by sulfate reducers either using sulfate or methanogens as e lectron acceptor. Sulfate reducers were also found to be important for acet ate consumption during the early phase of soil anoxia. Later on, however, m ethanogenic acetate consumption was much more pronounced. The application o f inhibitors with different specificity was helpful for elucidating the how of carbon and electrons during degradation of organic matter in anoxic ric e field soil. (C) 2000 Elsevier Science Ltd. All rights reserved.