Recombinant bioprocess optimization for heterologous protein production using two-stage, cyclic fed-batch culture

A two-stage, cyclic fed-batch bioprocess was designed, and its performance evaluated to improve rice alpha-amylase productivity by the yeast Yarrowia lipolytica SMY2 (MatA, ade1, ura3, xpr2), ATCC 201847, containing a replicative plasmid coding for a rice alpha-amlyase. Transcription of the recombinant gene is controlled by the XPR2 promoter. The first stage (or growth stage) was operated in the fed-batch mode, and the growth medium, designed to maintain a constant high cell density (i.e., 60 g/l), was fed according to a predetermined and preprogrammed optimal feed rate which, in turn, maintained the specific cell growth rate at an optimal value (i.e., 0.1 h-1). Typically, when the volume in the first stage reached a preset value, a portion of culture broth (i.e., 55%) was transferred to the second stage (or production stage). The remaining cells in the growth stage were then fed with fresh growth medium according to the bioprocess control strategy developed, while induction of alpha-amylase expression and its production was taking place in the second stage. The second stage was also operated in the fed-batch mode, and the production medium designed to maintain a constant high cell density and high productivity of heterologous protein was fed at a predetermined and preprogrammed rate, which maintained the specific cell growth rate at an optimal level. The volumetric alpha-amylase productivity achieved (1835 units l-1 h-1) from the two-stage, cyclic fed-batch culture process was twofold higher than that of the fed-batch culture process. The genetic stability of the recombinant strain and the design of optimal media for growth and production stages are also critically important to a successful implementation of the two-stage, cyclic fed-batch process for production of heterologous protein.