Biodegradation and metabolic assimilation of poly (butylene adipate-co-terephthalate) (PBAT) by Gordonia sp. CN2K

The increasing environmental burden of biodegradable plastics such as poly (butylene adipate-co-terephthalate) (PBAT) necessitates a detailed understanding of their microbial degradation mechanisms. In this study, Gordonia sp. CN2K utilized PBAT as the sole carbon and energy source, with cell density increasing from 1.26 × 10⁸ to 6.26 × 10⁸ CFU mL⁻¹ over 90 days. PBAT degradation, determined by weight loss measurements, reached 52.8% within 45 days. ATR-FTIR analysis indicated ester bond cleavage and polymer backbone disruption, demonstrating chemical modifications in the PBAT polymer. SEM analysis revealed progressive surface erosion, confirming morphological deterioration during biodegradation. Metabolite profiling identified terephthalic acid (TPA), adipic acid (AA), and oligomeric intermediates, all of which supported bacterial growth as individual substrates. Notably, 1,4-butanediol was not detected in the medium, suggesting rapid uptake and metabolism. Enzyme assays revealed that esterase activity was induced exclusively in PBAT-grown cultures, with higher activity in the extracellular fraction, indicating surface-associated depolymerization. Intracellular enzyme analysis showed the presence of protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase, supporting the involvement of ortho-cleavage pathways in aromatic intermediate metabolism. Overall, the results demonstrate a coordinated degradation mechanism involving extracellular depolymerization and intracellular assimilation under substrate-dependent enzyme regulation. These findings highlight Gordonia sp. CN2K as a promising candidate for the biodegradation of PBAT and related copolyesters.