Resistance of Microbial Community in Activated Sludge to Nano‐Ag Stress Through Regulation of <i>N</i> ‐Acyl Homoserine Lactones‐Mediated Quorum Sensing

Nano-Ag is increasingly detected in WWTP due to its widespread application, posing a significant threat to microbial communities responsible for wastewater treatment efficiency. Prior studies have demonstrated that quorum sensing (QS) can modulate bacterial tolerance to various environmental stressors in sludge systems. However, the feasibility and mechanisms of N-acyl homoserine lactones (AHLs)-mediated QS regulation to improve the resistance of microorganisms in WWTPs to nano-Ag shocks have been unexplored. Hence, we conducted sequencing batch reactor experiments, and as expected, nano-Ag significantly reduced the treatment performance of bioreactors. However, with the addition of AHLs (C6-HSL, C10-HSL, and C14-HSL) in the bioreactors, the microbial resistance in activated sludge to nano-Ag stress had been evidently enhanced, including the restoration of the sludge morphology, settleability, biomass and extracellular polymeric substances (EPS), as well as the treatment performance of bioreactors on removals of ammonium nitrogen (NH₄ ⁺-N), chemical oxygen demand (COD), and suspended solids. The joint analysis of metagenomics, metatranscriptomics, and metametabolomics indicated the multifunctional bacteria (e.g., Amaricoccus, Hydrogenophaga, and Brevundimonas) played a very important role during the regulation of AHLs-mediated QS, which harbored functional genes associated with nitrogen metabolism, carbon metabolism, silver resistance, and AHLs response. The upregulation on glutathione-dependent metabolisms (e.g., glutathione-oxidized glutathione redox cycle) and biosynthesis of EPS (e.g., poly-N-acetylglucosamine) were beneficial for the enhancement of microbial resistance to nano-Ag. This study provided a potentially feasible strategy and important theoretical basis to enhance the robustness and restore the function of microorganisms in wastewater treatment systems by using AHLs-mediated QS regulation.