CHANGES IN PROTEIN SECRETION OF ASPERGILLUS-NIGER CAUSED BY THE REDUCTION OF THE WATER ACTIVITY BY POTASSIUM-CHLORIDE

The effect of the rapid reduction of the water activity (a(w)) on the extracellular protein and amylolytic activity of Aspergillus niger was studied. An a(w) value gradient from 0.90 to 0.99 in KCl solutions wa s applied for the mycelium treatment. It was found that the a(w) reduc tion considerably influenced the protein secretion. This phenomenon wa s dependent on the age of the treated mycelium and the range of the a( w) gradient. The highest protein and enzyme secretion yields were obta ined at a(w) = 0.98 using a 72-h old mycelium. In comparison with the non-treated mycelium, the increase in the secretion amounted to about 60% for the amylolytic activity and 37% for the soluble protein, respe ctively. It was shown that the mycelium incubated in KCl solutions of an a(w) value from 0.90 to 0.99 had the ability for regeneration in fr esh CZAPEK-DOX medium. The effect of the osmotic shock on the protein secretion was limited only for the treated cell population and decline d in the mycelium which was regenerated after the transfer into the cu lture medium.