Mechanism of electricigenic respiration mediated by electron transfer mediator of Klebsiella oxytoca d7

Abstract

Electricigenic respiration is a new microbial metabolism discovered recently in an anaerobic environment lacking common electron receptors such as oxygen and others, in which some bacteria utilize extracellular electron transfer system. One electricigen, Klebsiella oxytoca d7, was isolated and confirmed its ability of electricigenic respiration in previous study, but its process and mechanism from intracellular respiratory chain to extracellular electron acceptors were not clear. In this paper, a microbial fuel cell (MFC) of this pure bacterium was constructed, and the main mechanism of electron transfer via the electron transfer mediators (ETMs) during electricity generation process of the bacterium was explored. The results show the ETMs can only be generated with the circuit on, and its contribution to the total electricity generation was much greater than that when the carbon source was insufficient. The redox potential of the ETMs of the K. oxytoca d7 was about −250 mV. The electrons were intercepted during the transfer from NADH to coenzyme Q and flow to the extracellular electron acceptors. The site of electron interception in the ETMs was only dependent on the redox potential of the ETMs secreted by the electricigens. Electrons were transferred from carriers in intracellular respiratory chain and with slightly higher redox potential than ETMs to ETMs. Normally the contribution of extracellular electron transfer mediated by ETMs to the total electricity generation amounted to more than 60%, indicating the process directly affected the conversion of organic substance in anode chamber and the electricity generation performance of the MFC.