Anaerobic Degradation\nof Aromatic and Aliphatic Biodegradable\nPlastics: Potential Mechanisms and Pathways

Biodegradable plastics (BDPs) have been widely used as\nsubstitutes\nfor traditional plastics, and their environmental fate is a subject\nof intense research interest. Compared with the aerobic degradation\nof BDPs, their biodegradability under anaerobic conditions in environmental\nengineering systems remains poorly understood. This study aimed to\ninvestigate the degradability of BDPs composed of poly(butylene adipate-<i>co</i>-terephthalate) (PBAT), poly(lactide acid) (PLA), and\ntheir blends, and explore the mechanism underlying their microbial\ndegradation under conditions of anaerobic digestion (AD). The BDPs\nreadily depolymerized under thermophilic conditions but were hydrolyzed\nat a slow rate under conditions of mesophilic AD. After 45 days of\nthermophilic AD, a decrease in the molecular weight and significant\nincrease in the production of methane and carbon dioxide production\nwere observed. Network and metagenomics analyses identified AD as\nreservoirs of plastic-degrading bacteria that produce multiple plastic-degrading\nenzymes. PETase was identified as the most abundant plastic-degrading\nenzyme. A potential pathway for the anaerobic biodegradation of BDPs\nwas proposed herein. The polymers of high molecular weight were subjected\nto abiotic hydrolysis to form oligomers and monomers, enabling subsequent\nmicrobial hydrolysis and acetogenesis. Ultimately, complete degradation\nwas achieved predominantly via the pathway involved in the conversion\nof acetic acid to methane. These findings provide novel insight into\nthe mechanism underlying the anaerobic degradation of BDPs and the\nmicrobial resources crucial for the efficient degradation of BDPs.