[Effect of the medium composition on the synthesis of protease by Aspergillus sp]

The main regulatory mechanisms controlling the synthesis of neural protease in batch cultures of a strain of Aspergillus were studied. Protease was inducible in this strain. No activity appeared during the trophophase when the organism was grown in a minimal medium, unless an inducer was added. Gelatine had the best induction effect among all the tested substances. The growth kinetics and enzyme production in a culture medium containing gelatine as the sole carbon and nitrogen source was determined. In spite of these results, protease activity was clearly detectable during the idiophase in absence of an external inducer. Furthermore, the addition of gelatine to cultures during the idiophase resulted in a decrease of the enzyme activity. This behaviour could be due to internal autoinduction generated by accelerated protein turnover of the nitrogen starved cells. The addition of gelatine probably reduced the protein starvation. Protease synthesis was sensitive to repression by rapidly assimilable carbon sources such as glucose and glycerol. Ammonia also caused an important repression, while nitrate and amino nitrogen had no effect. It was concluded that the synthesis of this enzyme is controlled by induction, catabolite repression, and ammonia repression, and that the enzyme production period could be adjusted by adequate formulation of the culture medium.