Production of poly(3-hydroxybutyrate) by recombinant bacteria

摘要

In order to improve the production of poly(3-hydroxybutyrate) [P(3HB)], two different recombinant bacteria, Escherichia coli and Alcaligenes eutrophus were investigated. Firstly, recombinant E. coli harboring a stable high copy number plasmid pSYL107 containing the A. eutrophus polyhydroxyalkanoate (PHA) synthesis genes and E. coli ftsZ gene was employed for the production of P(3HB) by fed-batch culture in a defined medium. Suppression of filamentation by overexpressing the cell division protein FtsZ allowed the production of P(3HB) to a high concentration of 104 g/L, and P(3HB) content of 70percent with high productivity of 2 g P(3HB)/L-h in a defined medium, which was the highest value reported to date by employing recombinant E. coli. Secondly, wild P(3HB) producer A. eutrophus was metabolically engineered to amplify the activities of the three enzymes, PHA synthase, beta-ketothiolase, and NADPH-dependent reductase, involved in the synthesis of P(3HB). The A. eutrophus PHa synthesis genes were cloned into a broad-host-range plasmid pVK101 and the constructed vector system was transferred into A. eutrophus by electroporation. In flask culture, the final cell concentration of recombinant A. eutrophus increased with decreasing carbon/nitrogen (C/N) molar ratio. For the fixed C/N molar ratio, the concentrations of cell and P(3HB) were increased with increasing glucose concentration. Comparison of cell growth and P(3HB) production by recombinant and wild type A. eutrophus in batch cultures showed that the final P(3HB) concentration, P(3HB) content, P(3HB) synthesis rate were all higher in the recombinant strain compared with the wild type.