Metabolic flux change in <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> L17 by anaerobic respiration in microbial fuel cell

The metabolic flux in microbial fuel cells (MFCs) is significantly different from conventional fermentation because the electrode in MFCs acts as a terminal electron acceptor. In this study, the difference in the carbon metabolism of Klebsiella pnuemoniae L17 (Kp L17) during growth in MFCs and conventional bioreactors was studied using glucose as the sole carbon and energy source. For metabolic flux analysis (MFA), the in silico metabolic flux model of Kp L17 was also constructed. The MFC bioreactor operated in oxidative mode, where electrons are removed by the anode electrode, generated a smaller quantity of reductive metabolites (e.g., lactate, 2,3-butanediol and ethanol) compared to the conventional fermentative bioreactor (non-MFC). Stoichiometric analysis indicated that the cellular metabolism in MFC had partially (or significantly) shifted to anaerobic respiration from fermentation, the former of which was similar to that often observed under micro-aerobic conditions. Electron balance analysis suggested that 30% of the electrons generated from glucose oxidation were extracted from the microbe and transferred to the electrode. These results highlight the potential use of MFCs in regulating the carbon metabolic flux in a bioprocess.