Pluripotency of endogenous AHL-mediated quorum sensing in adaptation and recovery of biological nitrogen removal system under ZnO nanoparticle long-term exposure.

The impacts of quorum sensing (QS) on nanoparticle (NP)-stressed biological nitrogen removal (BNR) system have seldom been addressed yet. In this study, the contributions of endogenous N-acyl-homoserine lactone (AHL)-based QS regulation to the BNR system's adaptation to the zinc oxide (ZnO) NP stress and its recovery potential were systematically investigated. Although 1 mg/L ZnO NPs exerted little impact on the BNR system, chronic exposure to 10 mg/L ones depressed the system's BNR performance which irreversibly impaired the nitrification process even when the system entered the recovery period with no NP added anymore. Meanwhile, ZnO NPs exhibited hormesis effects on the production of AHLs and extracellular polymeric substance (EPS), and activities of superoxide dismutase and catalase. During the ZnO NP exposure period, C-HSL, C-HSL, and C-HSL were discovered to be positively associated with nitrogen removal efficiency, tightly-bound EPS production, and antioxidase activities. Besides, the shifts of Nitrospira, Dechloromonas, Aeromonas, Acinetobacter, Delftia, and Bosea were expected to determine the AHL's dynamic distribution. During the system's recovery stage, Dechloromonas replaced Candidatus_Competibacter as the dominant denitrification-related genus. Dechloromonas abundance elevated with the increased contents of C-HSL in the aqueous and EPS phases and C-HSL in EPS and sludge phases, and were expected to promote the activities of BNR-related and antioxidant enzymes, and the EPS production to assist in the recovery of the impaired system's BNR performance. The QS-related BNR genera exhibited higher resilience to ZnO NPs than quorum quenching-related ones, indicating their critical role in nitrogen removal in the restored system. This work provided an insight into the potential pluripotency of AHL-based QS regulation on the ZnO NP-stressed BNR system's adaptation and recovery.