BACKGROUNDThe incorporation of 4HB units into P(3HB) improves the material application potential as the copolymer exhibits a wide range of physical properties ranging from crystalline plastic to elastic rubber depending on the copolymer composition. Thus, the prospects of synthesizing P(3HB-co-4HB) copolymer with various compositions of 4HB would increase its effectiveness as biomaterial. RESULTSThe residual cell dry weight (RCDW) and PHA concentration obtained under optimized conditions, namely C/N ratio 30, K2HPO4 6.1 g L-1, incubation period 66 h, temperature 32 degrees C and volume-to-flask ratio 47/250 mL increased from 2.9 g L-1 to 4.9 g L-1 and 4.2 g L-1 to 7.6 g L-1, respectively. P(3HB-co-4HB) with varied M-n between 26 kDa and 270 kDa were successfully synthesized using combinations of oleic acid, 1,6-hexanediol and/or 1,4-butanediol. The tensile strength and Young's modulus of the copolymers varied from 2 MPa to 24 MPa and 13 MPa to 192 MPa, respectively. T-m and T-g decreased with increasing 4HB molar fractions from 170 degrees C to 68 degrees C and 2.5 degrees C to -31 degrees C, respectively. CONCLUSIONOleic acid and (NH4)(2)SO4 was the best carbon and nitrogen source for PHA biosynthesis. P(3HB-co-4HB) copolymer with targeted 4HB molar fractions ranged from 0-65 mol% were synthesized using combinations of two or more carbon substrates by Cupriavidus sp. USMAA2-4 (DSM 19379) using mixture design. (c) 2013 Society of Chemical Industry