Production And Characterization Of Terpolyester Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) By Recombinant Aeromonas Hydrophila 4AK4 Harboring Genes PhaAB

Recombinant Aeromonas hydrophila 4AK4 harboring phbA and phbB (phaAB) genes encodingβ-ketothiolase and acetoacetyl-CoA reductase of Ralstonia eutropha produced a terpolyester of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 3-hydroxyhexanoate (3HHx) [P(3HB-co-3HV-co-3HHx)] from a mixtures of dodecanoic acid and propionic acid. Depending on the concentration of propionic acid in bacterial cultures, cell growth represented by cellular dry weight (CDW), P(3HB-co-3HV-co-3HHx) contents in dry cells and 3HV molar percentage in the terpolyester ranged from 0.43 to 3.29 g/L, 20.7% to 35.6%, 2.3 mol% to 7.1 mol%, respectively. Number average molecular (Mn) weights of the terpolyesters were 303,000 to 800,000, independent from monomer fraction content. This terpolyester was characterized by nuclear magnetic resonance (NMR), gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and stress-strain measurement studies. Results showed that the terpolyester had higher thermal stability and elongation at break compared with that of homopolymer poly(3-hydroxybutyrate) (PHB) and its copolymers P(3HB-co-5mol%3HV) and P(3HB-co-12mol%3HHx). In addition, the terpolyester had lower melting (T_m) temperatures and enthalpy of fusions (ΔH_m) than PHB did.