Quinoline is a typical polycyclic aromatic nitrogen heterocyclic compound, that is widely found in pharmaceutical, agricultural and coking wastewaters, with good solubility and low biodegradability (Wang et al., 2020). With its widespread availability, it has become a common contaminants in groundwater and soil, and is acutely toxic to aquatic organisms such as fish, Daphnia and green algae (Zhang et al., 2022). It can have a serious impact on human health through the food chain. Therefore, the effective removal of quinoline from wastewater has become a challenge.

To date, the main methods for treating wastewater containing quinoline are biodegradation (Zhang et al., 2020); and physicochemical degradation, as well as the use of advanced oxidation or biocatalysts (Luo et al., 2020). Among them, biodegradation has problems such as low efficiency and complexity; physicochemical degradation has high degradation efficiency, but its cost is high, and it easily causes secondary pollution; and biocatalysts are stable and can adapt to various extreme environments, but, it is difficult to achieve successful breeding and batch industrial applications (Zhu et al., 2021).

Quorum sensing (QS) is a cell density-dependent communication-sensing system among microorganisms that can regulate the expression of a range of target genes in response to changes in population density and their interactions with transcription factors (Priya et al., 2022). Wang et al. investigated the effects of 12 AHLs on pure culture biofilms and wastewater biofilms during initial biofilm formation and showed that bacterial adhesion was enhanced by the addition of AHL reagents and that biofilms showed a faster QS response to most AHLs (Wang et al., 2021a). Inaba et al. tested the effect of indole and four types of indole, 2-hydroxyindole (2-HI), 4-HI, 6-HI and isatin on biofilm formation in Streptococcus pyogenes and obtained results indicating that the addition of 4-HI and indole increased the biofilm formation of Streptococcus pyogenes (Inaba et al., 2020). Fu et al. promoted the stable operation of the biofilm formation process by immobilising and incorporating the QS strain Aeromonas erythropolis into the Moving-Bed Biofilm Reactor (MBBR) reactor system, where its incorporation resulted in increased levels of acyl-homoserine lactones (AHLs), EPS production and biofilm adherence (Fu et al., 2022). Thus, understanding the relationship between QS and biofilm formation is a complex issue.

Biofilms are involved in all aspects of our lives and are surface-adherent microbial communities themselves surrounded by and attached to inert or biological surfaces impregnated with liquid (Sahreen et al., 2022). Their main components are polysaccharides and proteins, and the biofilm method plays a crucial role in the treatment of wastewater. However, the biofilm formation process based on the induction of signal molecules by microbial communities has not been studied in depth; in particular, its regulatory mechanism is not yet understood. Therefore, this paper conducted an in-depth study by investigating the biofilm formation mechanism of the signal molecules C4-HSL and C6-HSL in the degradation process of quinoline by quinoline-degrading bacterial strains and clarified that C4-HSL and C6-HSL have an enhanced effect on the biofilm formation process during the degradation of quinoline, which lays a theoretical foundation for large-scale practical application.