In situ role of extracellular polymeric substances in microbial electron transfer by Methylomonas sp. LW13

Abstract

Extracellular polymeric substances (EPS), produced by microorganisms, establish the functional and structural integrity of microbial biofilms. In biological wastewater treatments, the transformation of pollutants largely relies on microbial electron transfer. As a bridge between the microbial cytomembrane/cytoderm and terminal electron acceptors, the role of EPS in microbial electron transfer cannot be ignored. However, due to the complexity of its composition, the in situ function of EPS in extracellular electron transfer is still unclear. In this work, we constructed an epsH gene knockout mutant of Methylomonas sp. LW13 with significantly reduced EPS formation. The content of protein and polysaccharide, two major components of EPS, of the ΔepsH mutant and wild-type during different growth stages were compared. The redox signal and in situ Au reduction of the ΔepsH mutant were obviously stronger than those of the wild-type, which suggested that EPS can hinder extracellular electron transfer in this system. Although redox activity was detected in EPS, high faradaic resistance of EPS was demonstrated. Our results enlighten the in situ role of EPS in extracellular electron transfer with the help of molecular manipulations and provide insights into how to regulate the microbial process of wastewater treatments.