N-Acyl-Homoserine Lactone (AHL)-Mediated Initial Adhesion Behaviors of Bacteria onto Plastics

The initial adhesion of microbes onto plastics is crucial for the subsequent formation of the plastisphere, which might be affected by signal molecules commonly present in bacteria-related environments that regulate cell-to-cell communication. Herein, the initial retention performance of E. coli onto six types of plastics, both without and with N-acyl-homoserine lactones (AHLs, a common signal molecule) at concentrations ranging from 10 ng/L to 100 μg/L in suspension, was determined to reveal the influence of signal molecules on the formation of the plastisphere. We found that AHLs coexisting in suspensions significantly enhanced bacterial adhesion performance onto plastics, regardless of plastic types and AHL types, with a more pronounced enhancement observed at higher AHL concentrations. This enhanced bacterial adhesion induced by AHLs also held true in solutions containing humic acid, in river water, and in sewage. AHLs stimulated the synthesis of EPS, enhanced EPS hydrophobicity by altering the protein/polysaccharide ratio and its secondary structures, and upregulated pathways related to flagellar assembly, quorum sensing, protein production, and biofilm formation, thereby enhancing bacterial adhesion capability onto plastics. Moreover, AHLs adsorbed onto plastic surfaces could induce chemoattraction effects, further promoting bacterial adhesion performance. Obviously, through various mechanisms, the signal molecules greatly influence the initial adhesion of bacteria onto plastics in aquatic systems.