The key factor is low operating cost for large scale PHBV production process. As so far, the production scale of PHA is far less than that of pertrolem-based polymers. The main cause is that the yield and productivity of PHA production are relatively low. This work intends to develop improved PHBV producer and more effective fermentation techniques. In poin of producing strain, the biosynthesis of PHBV depends on the flux of central metabolism pathway and precursor supply. Intensive research on the physiology, biochemistry and molecular genetics of the metabolism of PHBV has revealed a dramatic increase of our knowledge on the biosynthesis of this polyesters in bacteria. Using these knowledge, various metabolic engineering studies have been carried out to develop improved PHBV producer. Moreover, fermentation technology for the engineered strain should be established. High cell density cultivation of the PHBV producer is carried out as well as biosynthesis of PHBV with higher efficiency.

To get improved PHBV producer by using metabolic engineering strategies and to establish more effective fermentation technology by optimizing techniques of PHBV production. Finally, to produce PHBV with low cost in industrial scale.