New Insights into the Persistent Shock Resistance of Anaerobic Granular Sludge Based on Quorum Sensing Regulation: A Novel Gene Regulatory Mechanism

Anaerobic granular sludge (AnGS) is valuable for the treatment of high concentration organic wastewater but is hampered from further development by poor stability. Quorum sensing (QS) has been shown as an effective strategy to enhance the stability of AnGS, whereas the long-term resistance and underlying mechanisms remain uncertain. This work investigates the reinforcing effect of the QS on AnGS and the internal regulation mechanisms. The chemical oxygen demand (COD) removal was maintained at preshock level (90-93%) after multiple temperature shocks in the N-acyl-homoserine lactones (AHLs)-induced system. AHLs-mediated QS led to an increase in gene abundance of the four hydrophobic amino acids with protein (PN) increasing by 33.1%, which optimized the construction of the protective barrier of extracellular polymeric substances (EPS). AHLs also reshaped the functional microbial community and enhanced metabolic activities, promoting both the hydrogenotrophic and methanotrophic methanogenic pathways. In addition, the abundance of Geobacter and Methanothrix was increased by 4.4% and 2.3% under the stimulation of exogenous AHLs, which enhanced the direct interspecies electron transfer (DIET) pathway. This study provides a strategy for enhancing the stability of AnGS in the face of environmental shocks and gives a comprehensive theoretical foundation for exogenous AHLs-mediated QS regulation of anaerobic biological treatment.