Quorum-sensing-mediated optimization of cathodic biofilms for enhanced chlorobenzene removal in microbial electrolysis cells.

Microbial electrolysis cells (MECs) exhibit notable potential for treating refractory chlorinated organic pollutants by creating favorable redox conditions for microbial activity. However, the high sensitivity of biofilm properties to environmental fluctuations limits practical MEC applications. In this study, we investigated the effects of N-acyl-homoserine lactone (AHL)-mediated quorum sensing on MEC performance for chlorobenzene (CB) biodegradation and elucidated the underlying mechanisms. N-butyryl homoserine lactone (C4-HSL) and N-hexanoyl homoserine lactone (C6-HSL) enhanced CB removal during the start-up and operation phases. The reaction rate constants of AHL-treated groups (0.0937-0.5672 h-1) were significantly higher than those of the control group (0.0830-0.3906 h-1), accompanied by 23%-35% improvements in average dechlorination efficiencies. Of the tested AHLs, C4-HSL showed a more pronounced enhancement in biofilm characteristics. It promoted extracellular polymeric substance production and modulated its composition, thus strengthening biofilm resistance to CB stress and facilitating the formation of a robust biofilm with high cell viability. In addition to enriching Achromobacter (7.06%) and Thermomonas (8.75%), C4-HSL induced greater functional potential for cathodic electron uptake than C6-HSL, with a 2.85-fold increase in ccmG(dsbE) abundance and 1.79-4.38-fold enrichment of type IV pilus assembly genes, while also elevating the abundance of electron transport chain genes (237.51-3876.86 versus 42.26-1298.89 RPKM). Moreover, benzoate degradation and citrate cycle pathways were identified as key processes involved in CB elimination. Our findings provide mechanistic insights into how AHLs influence MEC efficacy based on biofilm structural and functional analyses, thereby advancing the deployment of MECs for efficient groundwater purification.