Size- and polymer-dependent toxicity of microplastics on Achromobacter-mediated polychlorinated biphenyl biodegradation: Gene suppression, oxidative stress, and morphological responses.

内容摘要

The ubiquitous presence of microplastics (MPs) in polychlorinated biphenyl (PCB)-contaminated environments may hinder microbial bioremediation through adsorption and toxicity effects; however, their specific effects on PCB-degrading bacteria remain unclear. In this study, the effects of polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), each at particle sizes of 25 μm and 250 μm, on the growth and Aroclor 1242-degrading capability of the resuscitated strain Achromobacter sp. HR2 were systematically evaluated. In addition, MP-induced alterations in the expression of functional genes, antioxidant enzyme activity, and morphological and physiological characteristics were assessed. The results revealed that MPs significantly inhibited microbial growth and PCB degradation in a size-dependent manner, with PS25 causing the greatest inhibition. Transcriptional analysis showed significant downregulation of key degradation genes (bphB, bphD, pobA, pcaGH, and pcaB) in MP-amended groups, with PS25 eliciting the most pronounced repression. MPs also induced elevated levels of intracellular reactive oxygen species and malondialdehyde, accompanied by enhanced activities of superoxide dismutase and catalase, indicating activation of the bacterial antioxidant defense system. Morphological and physiological disturbances were more pronounced with smaller (25 μm) MPs. This study provides valuable insights into the evaluation of microbial bioremediation performance in environments co-contaminated with MPs and PCBs.