PET degradation by Acinetobacter sp. W107 from plastic-polluted Tanggou River, mediated by the key esterase EstZ

Polyethylene terephthalate (PET) microplastic pollution poses significant threats to organisms and ecological health, and microbial degradation has emerged as a promising bioremediation strategy. This study isolated 85 bacterial strains from plastic-contaminated sludge and wastewater, and screened them for growth on PET granules as the sole carbon source. Three positive strains W106, W107, and SG211 were obtained; W107, identified as Acinetobacter sp. based on phenotypic and biochemical characteristics, showed the highest degradation efficiency. FTIR and HPLC confirmed the depolymerization of PET with the detection of terephthalic acid (TPA), while SEM verified the physical erosion of PET granules. The esterase gene estZ with 100% amino acid identity to Acinetobacter soli strain M3-1-68 EstB was cloned from Acinetobacter sp.W107 and recombinantly expressed in Escherichia coli BL21 (pET-28a). The recombinant strain (Rm-W107) enhanced PET degradation, with 6.87-fold higher TPA release over 5 days than cell-free controls, verifying EstZ's role in PET hydrolysis. Recombinant Estz (Rm-EstZ) had optimal activity at 40°C and pH 6.5, activated by 1 mM Fe³ ⁺ and 5 mM Fe²⁺ but inhibited by Zn²⁺ and Ca²⁺. Kinetic analysis showed moderate p-NPA substrate affinity (K_m = 4.917 ± 1.001 mM). These findings expand the repertoire of PET-degrading microorganisms, provide new insights into enzymatic bioremediation mechanisms, and highlight the whole-cell biocatalyst's potential for industrial plastic waste management.