Hydrogenophilic dechlorinating bacteria were shown to catalyze H(2) production by proton reduction, with electrodes serving as electron donors, either in the presence or in the absence of a redox mediator. In the presence of methyl viologen, Desulfitobacterium- and Dehalococcoides-enriched cultures produced H(2) at rates as high as 12.4 mu eq/mgVSS (volatile suspended solids)/d, with the cathode set at -450 mV vs. the standard hydrogen electrode (SHE), hence very close to the reversible H(+)/H(2) potential value of -414 mV at pH 7. Notably, the Desulfitobacterium-enriched culture was capable of catalyzing H(2) production without mediators at cathode potentials lower than -700 mV. At -750 mV, the H(2) production rate with Desulfitobacterium spp. was 13.5 mu eq/mgVSS/d (or 16 mu eq/cm(2)/d), nearly four times higher than that of the abiotic controls. Overall, this study suggests the possibility of employing dechlorinating bacteria as hydrogen catalysts in new energy technologies such as microbial electrolysis cells. (C) 2010 Elsevier Ltd. All rights reserved.