Distinct impact of polystyrene microplastics on six species of common pathogenic and probiotic bacteria and their boosting support to <i>Vibrio cholerae</i> 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 <i>Vibrio cholerae</i> proliferation. The results revealed that PS-MPs (100 nm to 5 μm, 0.1-100 mg L^-1) promoted the reproduction of <i>V. cholerae</i>, but blocked the growth of <i>Vibrio parahaemolyticus</i>, <i>Klebsiella pneumoniae</i>, <i>Klebsiella oxytoca</i>, <i>Staphylococcus aureus</i>, and <i>Lactobacillus plantarum</i>, 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 <i>V. cholerae</i> and consequently increased the bacterial cell surface hydrophobicity and membrane fluidity, biofilm formation and self-aggregation capacity (<i>p</i> < 0.05). Comparative transcriptome analysis uncovered significantly up-regulated metabolic pathways in <i>V. cholerae</i> 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. <i>In vitro</i> cell model experiments showed that the pre-exposure significantly increased the adhesion and invasion percentages of <i>V. cholerae</i> on human Caco-2 cells (<i>p</i> < 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 <i>V. cholerae</i>, a leading waterborne pathogen worldwide.