The feasibility of batch-wise polyester degradation and recycling using recombinant Escherichia coli expressing PHB depolymerase (PhaZ).

This study investigates the feasibility of PhaZ (PHB depolymerase derived from Caldimonas manganoxidans) in developing the PHB degradation and recycling process. PhaZ can be efficiently expressed and secreted at an OD of 0.5 and using 0.05 mM IPTG. Extracellular PhaZ exhibited enzyme activity within the range of 20-30 U/L, with a specific activity of ca. 0.5 U/mg-protein. The study shows robust enzyme stability, enduring at least five months without degradation. Due to PhaZ's sensitivity to 3HB reported in this study, a batch-wise PHB degradation and recycling process is recommended. The results indicate that the timing of PHB addition in the batch-wise degradation process should consider the PHB/PhaZ ratio, with a suggested threshold of 500 to ensure sufficient PHB adsorption sites for recycling PhaZ. Ultimately, the research highlights the feasibility of polyester degradation and recycling using extracellular PhaZ, as demonstrated by the conversion of recycled poly(lactic acid) (r-PLA) into lactic acid.