13c Pathway Analysis for the Role of Formate in Electricity Generation By Shewanella Oneidensis MR-1 Using Lactate in Microbial Fuel Cells

Microbial fuel cell (MFC) is a promising technology for wastewater treatment. Basically, the microorganisms sticking on the anode of the MFC utilize various organic compounds from the wastewater as the electron donors to generate electricity, while in the meantime removing the organic compounds in the wastewater. The type of electron donors fed into MFCs affects the electrical performance, and mechanistic understanding of such effects is important to optimize the MFC performance. In this study, we used a model organism in MFCs, Shewanella oneidensis MR-1, and ¹³C pathway analysis to investigate the role of formate in electricity generation and the related microbial metabolism. Our results indicated a synergistic effect of formate and lactate on electricity generation, and extra formate addition on the original lactate resulted in more electrical output than using formate or lactate as a sole electron donor. Based on the ¹³C tracer analysis, we discovered decoupled cell growth and electricity generation in S. oneidensis MR-1 during co-utilization of lactate and formate (i.e., while the lactate was mainly metabolized to support the cell growth, the formate was oxidized to release electrons for higher electricity generation). To our best knowledge, this is the first time that ¹³C tracer analysis was applied to study microbial metabolism in MFCs and it was demonstrated to be a valuable tool to understand the metabolic pathways affected by electron donors in the selected electrochemically-active microorganisms.