Crosslinkable prepolymer-immobilized Humicola lutea for acid proteinase biosynthesis

Crosslinkable prepolymer (CLP) was shown to be an effective carrier for immobilization of acid proteinase producer Humicola lutea 120-5. Enzyme production by the immobilized fungal strain was studied in repeated batch experiments in shake flasks and in an airlift bioreactor. Gel bead inoculum volume of 20% (v/v) produced maximal proteolytic activity exceeding 900 U/ml in 10 successive 24-h transfers of semicontinuous shake-flask fermentation. CLP-immobilized system retained the capability to synthesize acid proteinases in a 15-day period with enzyme yield of 660-850 U/ml in 5 sequential batches of bioreactor operation. The supernatant medium obtained at any stage of the repeated batch cultures did not contain free cells. The growth tendency of the mycelium in the gel beads during both the growth and the productive phases was observed with scanning electron microscopy.