Ribonuclease production by free and immobilizedAspergillus clavatus cells

Abstract

Several fungal strains ofAspergillus andPenicillium were immobilized by cryopolymerization in polyvinyl alcohol cryogel beads.Aspergillus clavatus was the best producer of extracellular ribonuclease. Enzyme productivity and growth of free and immobilized cells in shake flasks and agitated bioreactor were studied. Ribonuclease production and growth behaviour depended on concentrations of glucose, peptone and soybean in the culture medium. Enzyme production was influenced by agitation and aeration intensity. In repeated batch, shake-flask cultures, the immobilized cells showed 2 to 3.5 times higher enzyme activity than free cells. The optimal conditions in a bioreactor were at 150 rev/min agitation speed and 0.5 vol/vol.min aeration. Enzyme productivity of immobilized cells (237 units/g dry mycelium.h) was 2.1 times higher than the productivity of free cells in a bioreactor, and 2.3 times higher than that of a shake-flask culture.