Nanoplastics pre-exposure to microbial consortium influencing their ability to degrade pollutants: “Stagnation effect” and “Self-recovery”

Nanoplastics (NPs) coexist with microorganisms in global water environmental systems, showing spatial-temporal differentiation. Therefore, studying the behavior of microorganisms previously exposed to NPs is particularly important. With 2,4-dichlorophenol (DCP)-degrading microflora as model microorganisms, this study found that higher dose (10, 100 mg/L) of polystyrene NPs pre-exposure inhibited bacterial DCP degradation prolonging the stagnation period, while lower dose (1 mg/L) of NPs on the contrary stimulated their degradation ability. The degradation delay coefficients (μ) showed a significant positive correlation with the duration of pre-exposure. Specifically, the μ values observed after 1 day, 3 days, and 9 days of pre-exposure to 10 mg/L NPs were 2.5, 2.9, and 3.8, respectively, while those for 100 mg/L NPs were 3.2, 4.0, and 5.1. In contrast, the control group without NPs exhibited a μ value of only 1.9. Pre-exposure caused NPs to enter bacterial cells, leading to oxidative damage, membrane impairment, and potential DNA damage. This carry-over toxicity suppressed the consortium's degradation efficiency of DCP. During the stagnation period, microorganisms were striving to redeem themselves, recovering their abilities of biofilm formation, chemotaxis and motility by upregulating the expression of wspA, mcp, and pilJ gene families, thus reinforcing inter-population regulatory cooperation, thereby restarting the DCP degradation. With the duration of pre-exposure to PS NPs increased, the recovery time required for bacterial communities also lengthened. It is crucial to pay attention to the biological responses to subsequent pollutants triggered by pre-exposure.