EFFECT OF ACETIC-ACID ON POLY-(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) SYNTHESIS IN RECOMBINANT ESCHERICHIA-COLI

The synthesis of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB- co-3HV)] copolymer by recombinant Escherichia coli was studied in the medium containing glucose and valeric acid as carbon sources. A recomb inant E. coli strain (fadR atoC) harboring a stable high-copy number p lasmid containing the Alcaligenes eutrophus polyhydroxy-alkanoate (PHA ) biosynthesis genes was constructed for the production of the copolym er P(3HB-co-3HV). Accumulation of acetic acid not only had a detriment al effect on cell growth but also decreased the flux of acetyl-CoA int o the P(3HB-co-3HV) biosynthetic pathway. Reducing specific growth rat e by increasing the initial acetic acid concentration resulted in enha nced copolymer synthesis due to less accumulation of acetic acid. Init ial acetic acid concentration of 50 mM was found to be optimal at 20 g /l glucose and 20 mM valeric acid concentration. The fraction of 3-hyd roxyvalerate (3HV) increased with decreasing growth temperature. The r atios of 3HV to 3HB in the copolymer could be controlled by altering t he concentrations of valeric acid and glucose in the medium. Catabolit e repression was in part responsible for the inefficient copolymer syn thesis. Various nutritional components were examined for their ability to relieve catabolite repression. An addition of oleic acid resulted in threefold increase of the 3HV fraction in the copolymer. An additio n of a small amount of tryptone and peptone considerably promoted P(3H B-co-3HV) synthesis.