Physiological responses and proteomic reprogramming of resuscitated Achromobacter sp. HR2 under polystyrene...

Microplastics (MPs) commonly co-occur with polychlorinated biphenyls (PCBs) in contaminated environments, yet their combined impacts on PCB-degrading microorganisms remain insufficiently understood. In this study, the responses of the resuscitated PCB degrader Achromobacter sp. HR2 to polystyrene MPs (25 μm; PS25), PCBs (Aroclor 1242), and low temperature were examined. PS25 exposure under PCB stress markedly reduced the culturability and viability of strain HR2 and intensified oxidative stress, as indicated by elevated lactate dehydrogenase release, reactive oxygen species production, and malondialdehyde accumulation, accompanied by decreased Na⁺/K⁺-ATPase activity. Pronounced morphological deformation and alterations in cellular biochemical composition were also observed. Although low temperature (4 °C) further exacerbated membrane damage, its effects on ATPase activity, oxidative stress responses, and cellular biochemical profiles were minimal relative to those observed at 30 °C under combined PS25-PCB stress after 20 days. Quantitative proteomic analysis revealed extensive cellular reprogramming under both PS25 exposure and combined PS25-PCB stress, characterized by upregulation of proteins associated with ATP-binding cassette transporters, quorum sensing, biofilm formation, and antioxidant defense, together with suppression of carbohydrate, energy, amino acid, and xenobiotic metabolism. Relative to PS25 exposure, combined PS25-PCB stress induced broader and more pronounced proteomic responses, indicating the deployment of condition-specific adaptive strategies. These findings provide mechanistic insights into how functional degraders cope with complex environmental stressors and underscore the potential of resuscitated bacteria as effective bioinoculants for remediating PCB-contaminated sites affected by MP pollution.