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• NPs entered the intracellular region and caused plasmolysis and cytoplasm outflow. • NPs stimulated the initial cell attachment and aggravated NF membrane biofouling. • Low NPs exposure promoted cell secretion, quorum sensing and homologous recombination. • High NPs condition induced cell lysis, metabolic inactivation and genomic DNA damage. The release of nanoplastics (NPs) into the environment is growing due to the extensive use of plastic products. Numerous studies have confirmed the negative effects of NPs on microorganisms, which poses uncertainties concerning their impact on nanofiltration (NF) membrane biofouling. This study investigated the initial cell adhesion process, NF membrane biofouling kinetic processes and bacterial responses of Pseudomonas aeruginosa (P. aeruginosa) exposed to varied NPs concentrations (0–50 mg·L−1). Transcriptome analysis demonstrated that low concentration of NPs (0.1 mg·L−1) promoted bacterial quorum sensing, energy metabolism, exopolysaccharide biosynthesis and bacterial secretion systems. Correspondingly, the polysaccharide content increased remarkably to 2.77 times the unexposed control, which served as a protective barrier for bacteria to avoid the impact of NPs-induced stress. Suppressed homologous recombination, microbial metabolic potentials and flagellar assembly were detected in bacteria exposed to a high concentration (50 mg·L−1) of NPs, mainly due to the triggered reactive oxygen species (ROS) generation, genomic DNA damage, and decreased energy production. Overall, enhanced formation of the extracellular polymeric substances (EPS) and aggravated membrane flux decline were observed when NPs interacted with the membrane surface by cell secretions (low NPs levels) or cell lysis (high NPs levels). These findings shed light on understanding the microbial metabolism mechanism and membrane biofouling propensity with NPs stress at both the molecular and gene levels. [Display omitted] [ABSTRACT FROM AUTHOR]

Biofilm formation is a complex and time-consuming process, especially the attachment and growth of anaerobic biofilm, which fundamentally determines the start-up of biofilm reactor. In this study, biosurfactant, rhamnolipid, was introduced into an anaerobic moving bed biofilm reactor (AnMBBR) to promote its start-up, and the results showed that AnMBBR with rhamnolipid (RMBBR) could be successfully started within 25 days. Compared to the control AnMBBR without rhamnolipid, the start-up time was shortened by about half, the attached biomass on biocarriers was increased to 1.5 times, and the pollutants removal efficiencies were all greatly improved in the start-up phase, especially NO 3 − increased from 86.76 ± 1.04% to 96.93 ± 0.73%, and then these gaps were reduced in the steady-state phase. Under the action of rhamnolipid, the adhesion force of the biofilm increased from 18.9 nN to 27.4 nN eventually, and the interfacial energy between biofilm and biocarriers was transformed from repulsion (6200 KT) to weak attraction (−100 KT) by the evaluation of the extended Derjaguin–Landau–Verwey–Overbeek theory, which significantly promoted the initial attachment of biofilm. The increased metabolic activity, key enzyme activity, extracellular polymeric substances (EPS) and quorum sensing behaviors evidenced that rhamnolipid stimulated microbial internal activities and then regulated biofilm growth process. Moreover, rhamnolipid also significantly enhanced the abundance of functional bacteria in terms of metabolism or quorum sensing, including Thauera , Methylomonas , Desulfomicrobium , Azoarcus , Leptonema. Rhamnolipid would also stimulate the expression of genes that related to membrane transport, biofilm formation and nitrogen metabolism. This work provided a promising strategy for the rapid start-up of anaerobic biofilm reactor. [Display omitted] •Rhamnolipid accelerated the start-up of anaerobic MBBR by promoting biofilm formation. •Multiple regulatory mechanisms of rhamnolipid on biofilm formation were first proposed. •Rhamnolipid changed functional and structural characteristics of cell membrane. •The interfacial energy between biofilm and biocarriers was reduced by rhamnolipid. [ABSTRACT FROM AUTHOR]