Electrochemical Monitoring of Metabolic Activity of Methane/Methanol Conversing Methylococcus Capsulatus (Bath) Cells Based on Extracellular Electron Transfer

Abstract

Bioconversion of methane to methanol by methanotrophs under mild conditions is a promising approach for efficiently utilizing methane. Here, we present an electrochemical technique based on open-circuit potential (OCP) measurements to monitor the metabolic activity of Methylococcus capsulatus (Bath), a representative methanotrophic model. This technique is based on the extracellular electron transfer (EET) mechanism, in which intracellular electrons in living cells are exchanged across the cell membrane with an extracellular electrode. Without using artificial electron mediators in our study, we observed that OCP shifted to negative when methane metabolism was activated. By manipulating the culture conditions with the absence or presence of copper supplement to regulate the expression of outer membrane cytochromes (OMCs), the cells with a high OMC expression level, known to serve as conduits for EET, responded with increased sensitivity to stimulation with excess NADH compared to the cells with a low OMC expression level. We, therefore, used the instinctive EET capacity of M. capsulatus (Bath) for real-time OCP measurement to monitor the bioconversion of methane to methanol. Our measurements showed that the OCP levels change with intracellular redox variations and reflect methanol production rates. Our findings may facilitate the development of a methanotrophic bioprocess that allows more effective and efficient control of intracellular redox status using OCP monitoring based on EET.

Keywords

• methane-oxidizing bacteria
• outer membrane cytochromes
• intracellular redox
• open-circuit potential