The enhanced effect and mechanism of endogenous sigma factor RpoF on bioelectricity generation in Pseudomonas aeruginosa-inoculated Microbial fuel cells (MFCs)

Abstract

Microbial fuel cells (MFCs) has attracted tremendous attention due to integrating clean energy generation and wastewater treatment. Electricigens are in charge of electron transfer and energy conversion, and therefore strain improvement is crucial for MFCs performance. Herein, the overexpression of sigma factor RpoF and the combined manipulation with other regulators (PmpR and RpoS) reinforced electricity generation of a model strain Pseudomonas aeruginosa PAO1. Next, RpoF was introduced into an isolate P. aeruginosa P2-A-12 with higher electroactivity, which not only yielded 3.2-fold increase in the maximal power density under non stress, but also generated 21.4 % improvement under 1.5 % NaCl. The comprehensive analysis at the levels of cells, metabolites and genes transcription ascertained its global regulatory mechanism, mainly including the enhanced biofilm formation by promoting cell attachment and cell-to-cell adhesion on the anode, more c-di-GMP and quorum sensing (QS) signal molecules accumulation, and the increase in phenazine-1-carboxamide (PCN), pyocyanin (PYO) and 1-hydroxyphenazine (1-OHPHZ) by controlling the expression levels of multiple genes involved in core biosynthesis and QS system. It was the first time to demonstrate the direct activation of RpoF on phzH responsible for PCN production and rhlR regulating N-butanoyl-HSL (C₄-HSL) synthesis. Bioinformatic analysis indicated that the complex biological function of RpoF was closely linked with the conservation and diversity of sequences from various microorganisms. These findings strongly substantiated that RpoF acted as an efficient element to simultaneously optimize P. aeruginosa traits (such as electroactivity and stress tolerance) suitable for the practical MFCs, also broadened the theoretical recognition on its regulatory mechanism.