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 was applied for the mycelium treatment. It was found that the a w reduction considerably influenced the protein secretion. This phenomenon was dependent on the age of the treated mycelium and the range of the a w gradient. The highest protein and enzyme secretion yields were obtained 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, respectively. 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 fresh CZAPEK-DOX medium. The effect of the osmotic shock on the protein secretion was limited only for the treated cell population and declined in the mycelium which was regenerated after the transfer into the culture medium.