Electric field optimizes bacterium-phage interactions to enhance biofilm adaptation and microbial function in...

Despite the promising potential of bio-electrochemical systems integrated with constructed wetlands (BES-CWs) for wastewater treatment, bacterium-phage interactions under electric field stress have been largely overlooked. This study utilized microcosm BES-CWs fed with synthetic wastewater containing sulfamethoxazole (SMX) as a model antibiotic. It elucidated the synergistic regulatory mechanisms underlying the "phage-biofilm-function" interplay under three direct current voltages (0.4 V, 1.0 V, and 3.0 V), and further revealed the role of phage-mediated metabolic regulation in pollutant removal and microbial resistance attenuation in BES-CWs. Electric field stress significantly reshaped bacterial and phage diversity as well as community composition, with the strongest effects observed at 1.0 V. Compared with open-circuit BES-CWs, electric field application markedly enhanced lactic dehydrogenase activity (1.57-2.87-fold), extracellular polymeric substance production (3.52-11.25-fold), and biofilm thickness (1.33-2.23-fold), thereby promoting bacterial metabolic activity and optimizing biofilm structure. This structural adaptation improved substrate diffusion and electron transfer, alleviating mass transfer limitations typically associated with thick biofilms. Furthermore, electric fields activated bacterial antiviral defense systems and intensified bacterium-phage interactions. This increased predation pressure facilitated genetic exchange and nutrient recycling, thereby enhancing the functional resilience of the microbial community under environmental stress. In addition, electric field application selectively enriched auxiliary metabolic genes associated with metabolism and SMX degradation, promoting pollutant removal while reducing bacterial resistance potential. Overall, these findings provide mechanistic insights into how electric fields regulate biofilm development and bacterium-phage interactions, offering a potential strategy for enhancing the ecological stability and treatment performance of constructed wetlands.