Enhancement of environmental microplastics (MPs) degradation via bacteria under stress conditions: key enzymes, pathways, and mechanisms

Microplastics (MPs) are an emerging pollutant that needs effective bioremediation strategies. Strategies, including microbial implementation, enzymes, and insect-mediated degradation, have been effectively deployed and reviewed for the biodegradation of MPs. Thus, this review focused on utilizing multiple stressors (biotic and abiotic) to enhance MPs biodegradation. MPs degradation mechanism, major enzymes involved, and stress-mediated bacterial responses are highlighted. The key routes for MPs biodegradation under various stress are covered. Furthermore, the applications of stresses on wastewater treatment plants (WWTPs) for real-world application are also considered. Thermus sp. is reported to remediate polystyrene (PS) by 43.7% at 40-80 °C stress, whereas pH stress showed enhanced low-density polyethylene (LDPE) biodegradation (9.9%) under B. krulwichiae. Salinity up to 3 M NaCl, when applied to Bacillus sp., showed 48 times higher protease content. Radiation UV-C on P. aeruginosa increased polyethylene/polystyrene (PE/PS) protease activity by 75.47%. The bacterial response to stress was reported to be mediated by enzyme upregulation, biofilm formation, and metabolic shifts. Targeted stress enhanced MPs biodegradation through specific bacterial adaptations and enzymatic activity. Particular stress requires a specific mechanism to accelerate bacterial MPs degradation. Future research should aim to explore the synergistic effects of combined stressors, conduct comprehensive ecological risk assessments, and implement large-scale field trials to ensure the sustainability and ecosystem compatibility of stress-mediated MPs bioremediation.