H.-M. Yu1,*, Z.-L. Tian1, Z.-Y. Shen1, M. Duan-Mu2, and Y.-S. Mao2
1 Department of Chemical Engineering, Institute of Biochemical Engineering, Tsinghua University, Beijing, 100084, P. R. China
2 Nan-Tian Group Company, Jiangsu Provance, 226511, P. R. China
Key words: poly-β-hydroxyburyrate (PHB), recombinant E.coli, yeast autolysis solution, organic nitrogen
Genetic manipulation can be used to solve some traditional chemical engineering problems in biochemical engineering such as in poly (β- hydroxybutyrate) (PHB) production. For reducing the high production costs of PHB, usually due to expensive raw materials, low productivity of process and complexity of recovery steps, PHB biosynthetic genes (phbCAB), Vitreoscilla globin gene (vgb) and lytic genes of phage λ with a S amber mutation (S-RRz) were simultaneously introduced into a same recombinant Escherichia coli by three different strategies, correspondingly because of the advantages of phbCAB in utilization of cheap raw materials and accumulation of high content PHB, the ability of vgb to enable a higher specific oxygen uptake rate by the cells, and the characteristics of S-RRz to realize the controllable cell lysis. A superior novel strain, VG1 (pTU14), was successfully constructed and selected, which contained vgb in the chromosomal DNA and S-RRz and phbCAB in the plasmid pTU14.
For further decrease the production cost of PHB, starch hydrolysate was used in place of glucose as a cheaper carbon source. At the same time, yeast autolysis solution was used to substitue the commercial yeast extract as organic nitrogen source. The producing conditions of yeast autolysis solution were focused. Some important factors during the autolysis, such as temperature, pH, stirring speed and water ratio, were optimized, and the mechanism of yeast autolysis was also discussed. Then, a set of shaking flask experiments were designed and completed for comparing the growth-results of VG1 (pTU14) between the using yeast autolysis solution and commercial yeast extract. Satisfactorily it was shown that the culture of VG1 (pTU14) using yeast autolysis solution as organic nitrogen source was better than that using commercial yeast extract.
Summing up above studies, the yeast autolysis solution made from the discarded beer-yeast possesses a promising prospect in the industrial production of PHB.
论文来源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004
