Batch and continuous ribonuclease production by immobilized Aspergillus clavatus cells in a bubble-column bioreactor

Ribonuclease production using immobilized cells (IC) of Aspergillus clavatus has been studied under batch, repeated-batch and continuous fermentation conditions in a bubble-column bioreactor and compared with production by free cells. Immobilization was achieved by the method of cryostructurization in polyvinyl alcohol beads. The effect of various aeration rates in a column bioreactor has been investigated. Enzyme production by IC [42,000 units (U).1(-1)] during batch fermentations was comparable to that of a free-cell system. The specific productivity of IC was 8.5 times higher than that of free cells. In repeated batch fermentation at various aeration rates, successful reuse of IC was obtained, with comparable levels of enzyme production. Continuous ribonuclease production was achieved for 44 days at 1 vvm aeration and a dilution rate of 0.01 h-1 with high volumetric productivity (450 U.1-1.h-1) and yield.