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

Terpolyester consisting of 3-hydroxybutyrate (3HB), 4-hydroxybutyrate (4HB) and3-hydroxyhexanoate (3HHx) abbreviated as P(3HB-co-4HB-co-3HHx), was produced byrecombinant Aeromonas hydrophila 4AK4 harboring polyhydroxyalkanoate (PHA) synthesisgenes phaPCJ. The monomer content of 4HB in the terpolyesters was dependent on theconcentration of 1,4-butanediol, ranging from 4.3 to 8.5 mol% in the presence of 5 to 25 g/L1,4-butanediol, respectively, accompanying by a decreasing 3HHx content from 22 to 17.6 mol%and a constant 3HB content of 74 mol% during growth in lauric acid containing mineral medium.Number average molecular weights of the terpolyesters were 440,000 to 550,000, much higherthan 220,000 of the copolyester consisting of 3HB and 12 mol% 3HHx commonly produced bywild type A. hydroxphila 4AK4. Thermal and mechanical properties of the above terpolyesterswere better than those of homopolyester poly(3-hydroxybutyrate)(PHB) and its copolymersP(3HB-co-7mol%4HB), P(3HB-co-12mol%3HHx). Moreover, physical properties of theterpolyesters changed with variations of monomer composition. The terpolyesters werecharacterized using nuclear magnetic resonance (NMR), gas chromatography (GC),gel-permeation chromatography (GPC), differential scanning calorimetry (DSC),thermogravimetric analysis (TGA) and stress-strain measurements. The introduction of 4HB and3HHx monomers into PHB enhanced the thermal stability , changed its crystallinity andflexibility compared with homopolyester PHB and their two monomer containing copolyesters.