Disruption of a recombinant yeast for the release of beta-galactosidase

A recombinant yeast, Saccharomyces cerevisiae, expressing Escherichia coli beta-galactosidase gene under the control of CYC1 constitutive promoter of the yeast, was disrupted in a continuous flow, high speed, bead mill for the release of intracellular beta-galactosidase (EC 3.2.1.23). Release of the beta-galactosidase activity was characterized with respect to glass bead loading in the grinding chamber (70-85% of chamber volume), diameter of the beads (0.25-0.75 mm), number of passes of the cell slurry through the mill (0-6 passes), flow rate of the slurry (25-250 mL.min-1), cell concentration in the slurry (5-20 gDW.L-1), the agitation rotor speed (1000-4000 rpm) and the pH of the slurry (pH 5-10). The optimal conditions for the release of the enzyme were pH 6.0-9.0, 85% loading of 0.5 mm diameter beads and an agitation speed of 2000 rpm. The enzyme release followed first-order kinetics. For otherwise fixed conditions, the extent of cell disruption increase with increasing bead load, number of passes and agitation rotor speed. Cell concentration did not affect disruption. The release of beta-galactosidase activity declined with increasing flow rate of the cell slurry through the mill, but the disruption rate constant increased with flow rate. Under optimal condition, three passes through the grinding chamber were sufficient to release all of the enzyme. In comparison with disruption in the bead mill, chloroform-sodium dodecyl sulfate induced lysis of cells was ineffective in releasing the enzyme quantitatively.