Signal competition versus metabolic inhibition: Divergent fates of antibiotic resistance genes under N-acyl-L-homoserine lactone-targeted quorum quenching in composting.

Quorum sensing (QS) mediates biofilm formation and antibiotic resistance gene (ARG) transfer via signaling molecules, yet whether disrupting QS via quorum quenching restrains ARG dissemination during composting remains unclear. Here, vanillin and eugenol were supplemented at the beginning and mature stages to regulate ARG dynamics. Initial vanillin application effectively disrupted QS pathways and enhanced the removal of ARGs and MGEs by over 20% and 40%, respectively. Mechanistically, vanillin and eugenol competitively bound to acyl-homoserine lactone (AHL) receptors, triggering transient AHL accumulation and enhancing the functional potential for extracellular polymeric substance (EPS) production and type IV secretion system. Vanillin subsequently suppressed bacterial adhesion and conjugation by reducing genes related to EPS secretion (e.g. wacL), conjugation pilus assembly (e.g. trbC), and flagellar motility (e.g. fliE). This suppression reduced the number of mobile high-risk ARGs and attenuated horizontal gene transfer dominated by Pseudomonadota and Bacillota. Additionally, vanillin suppressed vertical gene transfer at the mature stage via inhibiting the growth of Gram-negative ARG hosts. Conversely, eugenol inhibited respiratory complexes IV/V, blocked ATP synthesis and temperature elevation, weakening thermal inactivation of ARG hosts (e.g. Pseudomonadota) and elevating ARG abundance. These findings provide a targeted approach for source control of ARGs in organic waste valorization.