Distinct impact of polystyrene microplastics on six species of common pathogenic and probiotic bacteria and their boosting support to Vibrio cholerae proliferation

Along with the widespread application of plastics, the release of polystyrene microplastics (PS-MPs) into the environment raises concerns about the risks of PS-MPs to human health. Hence, in this study, we investigated for the first time the impact of PS-MPs with different diameters on six species of common pathogenic and probiotic bacteria and further deciphered molecular mechanisms underlying the boosting support of PS-MPs for Vibrio cholerae proliferation. The results revealed that PS-MPs (100 nm to 5 μm, 0.1-100 mg L^-1) promoted the reproduction of V. cholerae, but blocked the growth of Vibrio parahaemolyticus, Klebsiella pneumoniae, Klebsiella oxytoca, Staphylococcus aureus, and Lactobacillus plantarum, showing different size- and concentration-dependent action modes. The PS-MPs (100 nm to 5 μm, 100 mg L^-1) significantly reduced the negative charge on the cell surface of V. cholerae and consequently increased the bacterial cell surface hydrophobicity and membrane fluidity, biofilm formation and self-aggregation capacity (p < 0.05). Comparative transcriptome analysis uncovered significantly up-regulated metabolic pathways in V. cholerae after exposure to the PS-MPs (100 nm, 100 mg L^-1) for 8 h, leading to enhanced chemotaxis, flagellar motility, biofilm formation, energy metabolism and antioxidant defense. In vitro cell model experiments showed that the pre-exposure significantly increased the adhesion and invasion percentages of V. cholerae on human Caco-2 cells (p < 0.05). Overall, the results of this study not only fill the gaps in the interaction between the PS-MPs and common bacteria, but also highlight the amplified hazard of co-pollution by PS-MPs and V. cholerae, a leading waterborne pathogen worldwide.