In this study, phaZCma (1355-2842, accession No. AB038647) and an open reading frame (ORFCma, 1-1233, AB038647) from Caldimonas manganoxidans were co-expressed in E. coli BL21(DE3). ORFCma is proposed as a periplasmic substrate binding protein (PSBP) and may non-specifically assist the secretion of the PHB depolymerase PhaZCma. The in vivo function of ORFCma can be perceived by the enhanced growth of E. coli by the supplemental of Mg2+. The degradation rate and the substrate specificity of whole-cell E. coli/pORFPHAZ were investigated. The results showed that while PHB films can be completely degraded by an extra-cellular fraction of C. manganoxidans in 81 h, only 35 h was required for an extra-cellular fraction of E. coli BL21(DE3)/pPHAZ to do the same. Further improvement was achieved when 80% of the film was found to be degraded by E. coli BL21(DE3)/pORFPHAZ in 28 h while only 21 h was needed by co-expressing ORFCma with PhaZCma. Testing of the time course of 3-hydroxybutyrate concentration and the turbidity of degradation solutions showed that PhaZCma had both exo- and endo-enzymatic activity and has been demonstrated that recombinant PhaZCma can degrade at-least four different polyesters, poly(3-hydroxybutyrate) (PHB), poly(lactic acid) (PLA), polycaprolactone (PCL), and poly(butylene succinate-co-adipate) (PBSA).

生物降解, 大腸桿菌, 聚酯材料

Bio-degradation; Escherichia coli; Polyesters