Integration of the current delivered to the reactors in Fig. 3B and conversion of the values to concentrations of two-electron pairs gave 1.35 mM, 1.68 mM, and 2.86 mM two-electron pair equivalents delivered to nitrate- (8.5 h), DMSO- (15.5 h), and fumarate- (15.5 h) containing media, respectively. Quantification of metabolites using HPLC showed that 20 mM nitrate, 10 mM DMSO, and 15.1 mM fumarate were reduced by 8.5, 15.5, and 15.5 h, respectively. Thus, neutral red was the ITF 2357 source for 6.7% of the nitrate reduced, 16.8% of the DMSO reduced, and 18.9% of the fumarate reduced during the electrosynthesis. In all cases, the majority of the electrons that moved through menaquinol to a terminal reductase were derived from a source internal to the cell, most likely NADH via type I NADH dehydrogenase. When nitrate concentration dropped below our limit of detection (0.5 mM) at 8.5 h, the current remained at ∼−0.5 mA, most likely due to the commencement of nitrite reduction. E. coli is known to preferentially reduce nitrate with the stoichiometry 1MKH2 + 1NO3− → 1MK + 1NO2−, followed by a switch to nitrite reduction ( Lin and Iuchi, 1991), with the stoichiometry 3MKH2 + 1NO2− → 3MK + 1NH4 ( Abou-Jaoude et al., 1979).