Improving cell permeability and stimulating biofilm to release extracellular polymeric substances with lysozyme for enhanced acetate production in microbial electrosynthesis

Microbial electrosynthesis (MES) is a promising microbial electrochemical process based on biocatalysts for converting CO2 into chemical energy. However, Gram-positive electrochemically active bacteria with a thick nonconductive peptidoglycan layer can reduce extracellular electron transport (EET) efficiency for restraining MES performance. Here, we report a regulation method for reducing the peptidoglycan content via lysozyme treatment in MES with mixed culture, significantly enhancing cell permeability in biofilm. Furthermore, lysozyme treatment stimulates the cathodic biofilm to release extracellular polymeric substances (EPS), particularly an increase in the protein content of all EPS fractions for enhancing EET. The MES with 2 g L-1 of lysozyme treatment achieved the best cell permeability. The corresponding exoprotein content in EPS was also the highest (1.12 ± 0.04 mg L-1), improving the electron transfer efficiency of the biofilm in the MES and resulting in the highest acetate yield (0.16 g L-1 d-1), which was two times that of the control. Furthermore, the total amount of biocatalyst and the cathodic microbial community can be improved with lysozyme treatment. This study provides a new direction for altering the characterization of cathodic biofilms through lysozyme treatment to improve MES efficiency.