The reduction of selenite (Se(IV)) and tellurite (Te(IV)) by Escherichia coli was significantly enhanced by various quinone redox mediators (lawsone, menadione, anthraquinone-2-sulfonate, and anthraquinone-2,6-disulfonate). In the presence of 0.2 mM lawsone, over 99.1% Se(IV) and around 96.4% Te(IV) were reduced in 8 h, at average reduction rates of 9.1 and 7.6 mM g cell(-1) h(-1), respectively. Better mediated reduction of Se(IV) and Te(IV) were observed when lawsone concentration increased from 0.1 to 0.4 mM and cell concentration increased from 0.1 to 0.6 g l(-1), respectively. Transmission electron microscopy analysis revealed the formation of both intracellular and extracellular Se(0) nanospheres or Te(0) nanorods, and the presence of lawsone increased the formation and accumulation of extracellular precipitates. The efficient mediated microbial reduction of Se(IV)/Te(IV) may be exploited for pollution removal and biological nanomaterials production. (C) 2010 Elsevier Ltd. All rights reserved.