The capability of Anaeromyxobacter dehalogenans to reduce Se(IV) to Se(0) as a detoxification mechanism suggests a potential role of these ecologically important microorganisms in the biogeochemical cycling of selenium and the control of selenium contamination. However, the reduction of Se(IV) by the energetically versatile A. dehalogenans could be hindered by its ability to use alternative electron acceptors, particularly Fe(III) and humic substances which are ubiquitous in the environment. Indeed, the presence of Fe(III) partially inhibited Se(IV)-reducing activity. Nonetheless, reduction of both Se(IV) and Fe(III) proceeded simultaneously, a characteristic desirable for bioremediation efforts in many environments abundant with Fe(III). The enhancement of Se(IV) reduction by anthraquinone-2,6-disulfonate, a humic substance analog, is advantageous for microbial selenium biotransformation given the broad distribution of humic substances in natural environments, which could be exploited for the design of improved control strategies for selenium pollution. (C) 2010 Elsevier Ltd. All rights reserved.