Dynamic response of immobilized cells to pulse addition of L-valine in cyclosporin A biosynthesis.

A feeding strategy for L-valine was tested in the production of cyclosporin A (Cy A), a powerful immunosuppressive secondary metabolite, in celite-immobilized cells of the fungus Tolypocladium inflatum. This system has been previously shown to have promise over conventional submerged systems. Significant increase in Cy A biosynthesis was manifested in the immobilized cells when L-valine was added at 108 h (system C) and at 156 h (system D) during the exponential growth phase. However, no clearly stimulating effect of L-valine on Cy A titre was observed when the amino acid was supplemented at hour 60 (lag phase, system B) or when the valine was present from the start (system A), where system A = 100%, system B = 113%, system C = 253%, system D = 302%. The large contribution to the enhanced production of Cy A in systems C and D may be explained by the preferential channeling of L-valine to growth during the lag phase and to secondary metabolism during the late exponential phase of the immobilized cells.