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

This study investigates the feasibility of PhaZ_Cma (PHB depolymerase derived from Caldimonas manganoxidans) in developing the PHB degradation and recycling process. PhaZ_Cma can be efficiently expressed and secreted at an OD₆₀₀ of 0.5 and using 0.05 mM IPTG. Extracellular PhaZ_Cma 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_Cma'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_eff/PhaZ_Cma ratio, with a suggested threshold of 500 to ensure sufficient PHB adsorption sites for recycling PhaZ_Cma. Ultimately, the research highlights the feasibility of polyester degradation and recycling using extracellular PhaZ_Cma, as demonstrated by the conversion of recycled poly(lactic acid) (r-PLA) into lactic acid.