Biodegradation of diethyl terephthalate and polyethylene terephthalate by a novel identified degrader Delftia sp. WL-3 and its proposed metabolic pathway

Polyethylene terephthalate (PET), a synthetic polyester material made of diethyl terephthalate (DET) monomers, is widely used in plastic products of daily life and caused serious pollution to the global environment. Microbial metabolism is the major degradation pathway responsible for DET degradation in natural soil; however, the microbial DET degradation mechanism remains unclear. In this study, the newly isolated strain WL-3, identified as belonging to the genus Delftia, was found to be able to degrade 94% of 5 g l^-1 of DET and utilize it as the sole carbon source for growth within 7 days. Furthermore, strain WL-3 was capable of stable DET degradation under a wide range of pH values (6·0-9·0) and temperatures (20-42°C) with the optimal pH and temperature of 7·0 and 30°C respectively. Furthermore, the biochemical pathway of DET degradation by strain WL-3 was proposed based on the identified degradation intermediates. DET is first transformed into terephthalic acid (TPA) by the hydrolysis of two ester bonds, which is subsequently converted to protocatechuic acid (PCA) and further mineralized. SEM observations revealed obvious cracks on the surface of PET film after inoculation of 2 months with strain WL-3, indicating the strain's potential for the bioremediation of PET-contaminated environments.

Significance and impact of the study: This study demonstrates that Delftia sp. WL-3 can mineralize completely diethyl terephthalate by biochemical processes. The study reveals the metabolic mechanism of diethyl terephthalate biodegradation. Furthermore, the cracks on the surface of Polyethylene terephthalate film that form upon inoculation with strain WL-3 were observed using SEM. These results highlight the potential of the strain WL-3 in the bioremediation of environments contaminated with Polyethylene terephthalate or diethyl terephthalate.

Delftia sp.; biodegradation; bioremediation; diethyl terephthalate; metabolic pathway; polyethylene terephthalate.