Characterization of a starch-hydrolyzing α-amylase produced by Aspergillus niger WLB42 mutated by ethyl methanesulfonate treatment.

Abstract

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.