AHL-Mediated Quorum Sensing Drives Aerobic Granular Sludge Formation and Stability under Quinoline Stress

Aerobic granular sludge (AGS) is promising for refractory pollutant removal, whereas its application is constrained by long start-up periods and insufficient structural stability. Quorum sensing (QS) modulates bacterial community behaviors and plays a pivotal role in AGS formation and stabilization. Using quinoline as the target pollutant, this study successfully cultivated AGS. Moreover, we linked acyl-homoserine lactones (AHL)-based QS dynamics to EPS quantity/composition shifts during quinoline-stressed granulation. During granulation, the concentration of AHLs (C4-HSL and C8-HSL) increased with a significant upregulation of AHL-associated synthesis genes (mainly rhlI ) and sensing genes (especially cciR, sdiA and aphA ). Quinoline-triggered QS altered the composition of EPS, raising EPS content from 12.5 mg/g VSS to 97.5 mg/g VSS and the PN/PS ratio to 2.3, indicating enhanced granulation and improved particle stability. Further analysis revealed that the enriched hydrophobic amino acids and monosaccharides in EPS enhanced relative hydrophobicity of AGS, reduced surface negative charge, and eliminated the energy barrier, ultimately strengthening microbial aggregation. Furthermore, exogenous addition of 1 μM C8-HSL effectively improved granule stability by regulating EPS biosynthesis. This work provides the first mechanistic evidence that AHL-mediated QS can be harnessed to improve AGS formation and resilience under toxic stress, by modulating EPS composition and microbial community.