Dual Roles of Gram-Positive Bacteria in Biofilm Structure and Functionality in Microbial Electrochemical Systems

Gram-positive bacteria are essential for the structural stability and functionality of biofilms in microbial electrochemical systems (MESs). This study evaluated the effects of lysozyme-induced disruption of Gram-positive bacteria on the microbial electrolysis cell (MEC) performance and biofilm composition. Lysozyme treatment reduced biofilm thickness by 37.7% and biomass by 80% due to the peptidoglycan hydrolysis and increased cell lysis, leading to higher proportions of dead cells in both the anode (18.02 to 57.7%) and the cathode (21.9 to 55.2%) biofilms. However, the metabolic capacity of anodic microorganisms (59 to 360 Coulomb produced by 10¹⁰ microorganisms) was enhanced due to enhanced cell permeability and a looser biofilm structure that facilitated electron transfer. Conversely, the cathodic performance of the electron recovery efficiency decreased (from 81.97 to 70.92%), and the H₂ and CH₄ productions were reduced by 43 and 11%, respectively. This was attributed to the loss of key Gram-positive species and weakened microbial network connectivity. Network analysis revealed enhanced modularity at the anode with stabilized performance, whereas the cathode network was sparse and had impaired microbial interactions. These findings have accentuated the dual roles of Gram-positive bacteria in maintaining biofilm stability and microbial interactions, influencing discrete anode and cathode processes.