Fig. 3

Comparison of intracellular metabolite concentrations related to the TCA cycle in microbial cells growing on the MFC anode (pH 7.0: black bars, pH 5.5: gray bars, and pH 4.0: white bars). The metabolite concentrations (µmol g-cell⁻¹) were measured after 30 days’ operation. Error bars indicate ± standard deviation. The metabolic flow of organic acids (formate, acetate, propionate, butyrate and lactate) are shown. Acetyl-CoA and pyruvate relate to the metabolism of acetate by the TCA cycle in G. sulfurreducens (Mahadevan et al. 2006). Glutamate is one of the important metabolite in microbial nitrogen metabolism (Reitzer 2003). AMP adenosine-monophosphate, CoA coenzyme A, FAD flavin adenine dinucleotide, PYR pyruvate, Fd ferredoxin, MQ menaquinone, Pi phosphoric acid