Quorum sensing responses of activated sludge to free nitrous acid: Zoogloea deformation, AHL redistribution, and microbiota acclimatization.

Free nitrous acid (FNA) has been widely employed for improvement of wastewater management by altering sludge characteristic and function based on its polymer lysing and biocidal capacity. Sludge characteristic and function are commonly considered as the joint consequence of microbial individual behaviors and quorum sensing (QS) involved collective behaviours, but the role of the latter in FNA treatment was still as-yet-unidentified and addressed in this research. The results of sludge morphology and component characterized FNA-induced zoogloea deformation, including inner cell exposure, half of extracellular polymeric substances (EPS) reduction and adsorption site depletion. During zoogloea deformation, four acyl-homoserine lactones (AHLs), including C4-HSL, C8-HSL, C10-HSL and C12-HSL, transferred inward of microbiota, and their total contents reduced by 66% because of depressed signal production, augmented decomposer and recognition. Transcriptome analysis revealed that differentially expressed QS driven by AHL redistribution facilitated microbiota acclimatization including cellular motility and hydrolase synthesis for EPS consumption. Boosted motility may favor escaping from stress spot and moderating intercellular acidity based on cell motility test. Feasible EPS consumption provided nutrition for heterotrophic metabolisms testified by pure culture with EPS as sole nutrition. Our work thus comprehensively revealed QS behaviours responding to FNA and deepened the understanding to FNA treatment performance in wastewater management.