Co-Expression of ORFCma with PHB Depolymerase (PhaZCma) in Escherichia coli Induces Efficient Whole-Cell Biodegradation of Polyesters

Whole-cell degradation of polyesters not only avoids the tedious process of enzyme separation, but also allows the degraded product to be reused as a carbon source. In this study, Escherichia coli BL21(DE3) harboring phaZ(Cma), a gene encoding poly(3-hydroxybutyrate) (PHB) depolymerase from Caldimonas manganoxidans, is constructed. The extra-cellular fraction of E. coli/pPHAZ exhibits a fast PHB degradation rate where it only took 35h to completely degrade PHB films, while C. manganoxidans takes 81h to do the same. The co-expression of ORFCma (a putative periplasmic substrate binding protein that is within the same operon of phaZ(Cma)) further improves the PHB degradation. While 28h is needed for E. coli/pPHAZ to cause an 80% weight loss in PHB films, E. coli/pORFPHAZ needs only 21h. Furthermore, it is able to degrade at-least four different polyesters, PHB, poly(lactic acid) (PLA), polycaprolactone (PCL), and poly(butylene succinate-co-adipate) (PBSA). Testing of the time course of 3-hydroxybutyrate concentration and the turbidity of the degradation solutions over time shows that PhaZ(Cma) has both exo- and endo-enzymatic activity. The whole-cell E. coli/pORFPHAZ can be used for recycling various polyesters while ORFCma can potentially be a universal element for enhancing the secretion of recombinant protein.