PRODUCTION OF POLY(3-HYDROXYBUTYRIC ACID) BY RECOMBINANT ESCHERICHIA-COLI STRAINS - GENETIC AND FERMENTATION STUDIES

A number of Escherichia coli strains including K12, B, W, XL1-Blue, DH 5 alpha, HB101, JM109, and C600 were transformed with the stable high- copy-number plasmid pSYL105 containing the Alcaligenes eutrophus polyh ydroxyalkanoic acid biosynthesis genes, and were subsequently compared for their ability to synthesize and accumulate poly(3-hydroxybutyric acid) (PHB). The rate of PHB synthesis, the extent of PHB accumulation , and PHB yield from glucose varied considerably from one strain to an other. Strains XL1-Blue and B harboring pSYL105 synthesized PHB at the highest rate to a final concentration of ca. 7 g/L in complex medium containing 20 g glucose/L. With an aim to reduce the cost of the mediu m, the effect on PHB accumulation of supplementing a defined medium wi th complex nitrogen sources was examined. A PHB concentration of 81 g/ L could be obtained in 41 h from a pH-stat fed-batch culture of XL1-Bl ue(pSYL105) in a semidefined medium. When the availability of acetyl-C oA was increased by supplementing the medium with complex nitrogen sou rces, amino acids, or oleic acid, PHB synthesis by recombinant E. coli was enhanced.