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

Area of Science:

• Biotechnology
• Polymer Science
• Environmental Science

Background:

• Polyhydroxybutyrate (PHB) is a biodegradable polymer with potential applications but faces challenges in efficient degradation and recycling.
• Developing robust enzymatic processes is crucial for sustainable PHB management.

Purpose of the Study:

• To investigate the feasibility of using PhaZ_Cma (PHB depolymerase from Caldimonas manganoxidans) for PHB degradation and recycling.
• To characterize the enzyme's activity, stability, and optimal conditions for a recycling process.

Main Methods:

• Efficient expression and secretion of extracellular PhaZ_Cma were achieved under specific conditions (OD₆₀₀ of 0.5, 0.05 mM IPTG).
• Enzyme activity and stability were measured, and a batch-wise degradation process was designed considering enzyme sensitivity to 3-hydroxybutyrate (3HB).
• The PHB_eff/PhaZ_Cma ratio was optimized to ensure efficient PHB adsorption for recycling.

Main Results:

• Extracellular PhaZ_Cma demonstrated enzyme activity (20-30 U/L) and high specific activity (ca. 0.5 U/mg-protein).
• The enzyme exhibited remarkable stability, remaining active for over five months.
• A batch-wise process was recommended due to PhaZ_Cma's sensitivity to 3HB, with an optimal PHB_eff/PhaZ_Cma ratio of 500 for effective PHB adsorption.
• Recycled poly(lactic acid) (r-PLA) was successfully converted into lactic acid, demonstrating the process's utility.

Conclusions:

• Extracellular PhaZ_Cma is a feasible and stable enzyme for PHB degradation and recycling.
• The developed batch-wise process, considering enzyme sensitivity and optimal ratios, enables efficient polyester recycling.
• This research contributes to sustainable polymer management through enzymatic degradation and recovery.