Competition between methanogenesis and quinone respiration for ecologically important substrates in anaerobic consortia

Anaerobic consortia obtained from a wide variety of environments were teste d for oxidizing several ecologically significant substrates with the humic model compound, anthraquinone-2,6-disulfonate (AQDS), as terminal electron acceptor. All the substrates, including hydrogen, acetate, propionate, meth anol and lactate, were completely or partially converted to methane when bi carbonate was the only electron acceptor available. Addition of AQDS (20 mM ) to the cultures prevented methanogenesis in most cases and AQDS reduction became the preferred pathway. AQDS was shown to be toxic for methanogenesi s and this effect played an important role in enabling quinone-respiring ba cteria to outcompete methanogens. Furthermore, AQDS respiration is thermody namically more favorable than methanogenesis. All the consortia evaluated w ere capable of oxidizing hydrogen linked to the reduction of AQDS. Most ino cula tested were also able to oxidize acetate and lactate in the same way. When methanol was provided as an electron donor competition between methano genesis and acetogenesis occurred. Acetate accumulated from the latter proc ess was responsible for quinone respiration. These results suggest that qui none-respiring bacteria are ubiquitous and that quinones in humus may signi ficantly contribute to carbon cycling process by serving as a terminal elec tron acceptor for the anaerobic microbial oxidation of a wide variety of ec ologically important substrates. (C) 2000 Federation of European Microbiolo gical Societies. Published by Elsevier Science B.V. All rights reserved.