Enhanced rapid acclimation of nitrifying sludge to sulfamethoxazole stress via exogenous quorum-sensing signal molecules.

Nitrifying sludge is capable of simultaneous removal of high-concentration ammonia nitrogen and sulfamethoxazole (SMX). Quorum sensing mediated by acyl-homoserine lactones (AHLs) has emerged as a potential regulatory tool to modulate microbial community function and stress resistance. However, the effects of AHLs on nitrifying sludge under SMX stress remain unclear. This study aimed to investigate whether AHLs can facilitate the acclimation of nitrifying sludge under SMX exposure. Sequencing batch reactor experiment results demonstrated that under the shock loading of 500 μg/L SMX, the addition of 2 μM C6-HSL maintained significantly higher NH4+-N removal efficiency and nitrite accumulation rate, compared with the 2 μM 3-oxo-C6-HSL group, and the mixed addition group of C6-HSL and 3-oxo-C6-HSL. Meanwhile, under the action of C6-HSL, nitrifying sludge exhibited a steadily increasing SMX removal efficiency starting from Day 12, which was earlier than other groups. From a microscopic perspective, the individual addition of AHLs stimulated the secretion of EPS and the growth of functional bacteria, whereas the combined addition group resulted in the opposite effect. The combined addition of AHLs enhanced the capacity of converting nitrite to nitrate, while attenuating its denitrification ability. This study provides a theoretical basis for the rapid adaptation of biological processes to SMX-contaminated wastewater.