Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with co-expressed propionate permease (prpP), beta-ketothiolase B (bktB), and propionate-CoA synthase (prpE) in Escherichia coli

Abstract

Poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) are biopolymers produced by microorganisms and have commercial potential as bioplastics. The compositions of polymers influence their physical and mechanical properties. PHBV polymers with high composition of 3-hydroxybutyrate (3HB) are brittle. Increasing the fraction of 3-hydroxyvalerate (3HV) monomer in the PHBV can reduce the crystallinity, resulting in more flexibility. To increase the fraction of 3HV in PHBV and reduce the antibiotic supplementation to maintain the recombinant plasmid, we cloned the prpE gene encoding propionyl-CoA synthase, the vgb gene encoding bacterial hemoglobin (VHb), and the polyhydroxyalkanoates (PHAs) synthesis operon (phaCAB) in one recombinant plasmid transformed into Escherichia coli XL1-blue, termed CT-2E. The prpP gene encoding propionate permease and the bktB gene encoding beta-ketothiolase were also cloned to evaluate their effects on PHBV accumulated in E. coli containing phaCAB-vgb, termed CT-2-BP. The results showed that the 3HV fraction in PHBV and the molecular weight of PHBV increased when prpE was expressed in CT-2E, compared with E. coli containing phaCAB-vgb (termed CT-2). The polydispersity index (PDI) of the PHBV derived from CT-2-BP was 1.33, indicating that polymer uniformity was greater than that from CT-2, which had a PDI of 1.68. Compared with CT-2, the enthalpies and melting temperature of PHBV from CT-2E and CT-2-BP decreased, indicating the advantages of processing.