RESUMO
Aspergillus niger is the most commonly used fungus for commercial amylase production, the increase of amylase activity will be beneficial to the amylase industry. Herein we report a high α-amylase producing (HAP) A. niger WLB42 mutated from A. niger A4 by ethyl methanesulfonate treatment. The fermentation conditions for the amylase production were optimized. The results showed that both the amylase activity and total protein content reached highest after 48-h incubation in liquid medium using starch as the sole carbon source. The enzyme production reached maximum at temperature of 30°C, pH 7, with 40 g/L starch in the medium inoculated with 1.4% v/v spore. When 0.3% w/v urea was added to the liquid medium as a nitrogen source, the amylase activity was elevated by 20%. Nine monosaccharides and derivatives were tested for α-amylase induction, glucose was the best inducer. Furthermore, the enzymology characterization of amylase was conducted. The molecular weight of amylase was determined to be 50 kD by SDS-PAGE. The amylase had maximum activity at 45°C and pH 7. The activity could be dramatically triggered by adding 1 mM Co(2+), increased to 250%. The activity was inhibited by detergents SDS and Triton X-100. Six different brands of starch were tested for amylase activity, the results demonstrated that the more soluble of the starch, the higher hydrolyzability of the substrate by amylase.
RESUMO
The costs of amylase represent ca. 24 % of the expenditures in the starch industry and an increase in amylase production and/or activity will greatly cut down on production costs. In the present study, we obtained a high amylase-producing strain of bacteria, WangLB, and identified it as a member of the Bacillus genus based on 16S rDNA analysis. The fermentation conditions for amylase production in the strain were optimized, and the maximum amylase activity we obtained was 26,670 ± 1390 U/mL, under the optimized conditions of 48-h incubation in liquid starch medium, 35 °C, pH 10, 1 % v/v inoculum concentration, 20 g/L starch concentration, and 0.1 % w/v peptone. The influences of 16 small organic inducers on amylase production were tested, and the results showed that 20 mmol/L alanine greatly enhanced amylase production to 290 % of the baseline level. We also conducted an amylase enzymology analysis. The molecular weight of the amylase was 55 kD, determined by SDS-PAGE. The optimum temperature and pH for the amylase were 55 °C and pH 9, respectively. The enzyme also showed high activity over a wide range of temperatures (50-85 °C) and pH values (3-10), and the activity of the amylase was Ca(2+) independent. The kinetic parameters K m and V max were 0.37 ± 0.02 mg/mL and 233 U/mg, respectively. Finally, the amylase was applied to the hydrolysis of five different brands of starch. It was found that the hydrolyzability of the substrate by amylase increased along with starch solubility.
