The growth of Aspergillus niger (NRRL 1785) was investigated and monitored over a five-day fermentation period. Acid protease synthesis by this fungus was also investigated during the period. The effect of growth of Aspergillus niger on acid protease synthesis was determined. Some of the physicochemical properties of the acid protease were examined. The growth curve obtained for Aspergillus niger revealed four phases of growth which are the lag phase, the exponential phase, the deceleration phase and the death phase. Acid protease synthesis by Aspergillus niger increased in direct proportion to growth up to the early hours of the death phase. Maximum enzyme synthesis was obtained at the 96th hour of fermentation, which was 12 hours into the death phase. The acid protease synthesized had optimum pH of 4.0, while the enzyme was stable (60% relative activity and above) over a wide range of pH 2.5 - 5.5. The optimum temperature for acid protease was determined to be 500C. The enzyme was also stable up to this temperature (500C) at pH 4.0 for 1 hour. Calcium ions had activating effect on the acid protease while sodium and mercury ions had inhibitory effects. The results obtained in this paper show a direct correlation between the growth of Aspergillus niger and acid protease synthesis, hence the particular phase of growth of Aspergillus niger determines the extent of enzyme yield by the fungus.
Key words: Proteolytic enzyme; Acid protease; microbes; Aspergillus niger
(Global Journal of Pure and Applied Sciences: 2003 9(4): 523-528)