Metabolic shift of Klebsiella pneumoniae L17 by electrode-based electron transfer using glycerol in a microbial fuel cell

Abstract

Klebsiella pneumoniae is used widely for the production of value-added chemicals from glycerol, and is known as an exoelectrogen with an externally provided electron shuttle. In this study, the metabolic shift in K. pneumoniae L17 by the activation of electrode-based respiration was examined using microbial fuel cells (MFCs). The mRNA expression levels of the related enzymes for glycerol conversion were compared under electrode-driven anaerobic respirational conditions (i.e., MFC) and fermentative conditions (i.e., non-MFC). mRNA expression clearly responded to the electrode-based electron transfer with simultaneous current generation and changes in metabolite production. The NAD+-dependent pathways were activated and more acetate (21.7 vs. 14.6 mM), 3-HP (7.6 vs. 5.3 mM) and 1,3-PDO (45.5 vs. 38.1 mM) and less ethanol production were observed under MFC conditions than under non-MFC (39.6 vs 66.7 mM). Stoichiometric metabolic flux analysis was examined in MFC condition. These results suggest that electron excretion to the carbon electrode drives the metabolic pathway shift of K. pneumoniae L17, and can provide an active control strategy for the fermentative pathway of glycerol.