Abstract:
Amylases are used in numerous industrial applications and for starch conversion to value added products. The increasing demand for amylase in diverse industrial processes creates the need for isolating microbial strains with novel properties. An amylase producing thermotolerant Aspergillus fumigatus was isolated from soil samples after 120 h incubation on potato dextrose agar supplemented with 0.5% starch at 50°C. The ability of the amylase to grow and produce amylase under varying conditions of temperature, starch source, nitrogen source and mineral salts was evaluated. The Aspergillus sp. grew well and produced amylase at 55°C though maximum growth and amylase production was recorded after 96 h incubation at 30°C in a mineral medium containing 1% starch and 1.5% organic nitrogen concentration. Sorghum starch as carbon source elicited a better amylase production from the organism. A combination of inorganic (NH4Cl) and organic (soybean meal) nitrogen sources led to the synthesis of higher concentration of amylase in culture fluid. Amylase was optimally active at pH 6.0 and was acid stable at pH 4.5 retaining over 93% of its activity after 24 h. Optimal temperature for enzyme activity was at 60°C with approximately 65% of enzyme activity retained after 30 min incubation at 70°C. The amylase enzyme was slightly repressed by Fe2+ and Mn2+ but not inhibited by Cu2+, Co2+ and Hg2+ at a concentration of 2 mM. The highest hydrolytic activity of the Aspergillus fumigatus amylase was recorded for yam, followed by potato and cassava starches.
T.N. Nwagu and B.N. Okolo, 2011. Growth Profile and Amylolytic Activity of a Thermophilic Fungus
Aspergillus fumigatus Isolated from Soil. Asian Journal of Biotechnology, 3: 46-57.
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