Stability of extracellular proteinase productivity by Bacillus subtilis cells immobilized in PVA-cryogel

Viable Bacillus subtilis cells were entrapped in the PVA-cryogel beads as described earlier [J. Mol. Catal. B Enzym. 11 (2001) 671; Biomol Eng 17 (2001) 55], and applied for synthesis of extracellular proteases (subtilisin and metalloproteinase) in the repeated-batch process. The scope of the present study was to evaluate the dependence of the proteases biosynthesis yield and the immobilized preparation stability on the cells growth phase prior to the entrapment, and their initial concentration in the PVA-beads. Spatial distribution of B. subtilis microcolonies inside the beads, and the cell leakage from the carrier during successive batches were also determined. The depth of the bacterium growth and changes in the biomass content inside the beads were measured using an image processing system. It was observed that the growth rate, spores formation and the proteases biosynthesis by the immobilized B. subtilis cells were strongly affected by the PVA-cryogel microenvironment.