Elucidation of optimum culture conditions for cellulase production by thero-tolerant Aspergillus fumigatus isolated from heap of cassava peels
摘要
Temperature control is a very important and expensive unit operation in enzyme production. The use of microbial strains that can efficiently produce enzymes over a wide range of temperature will minimize the need for temperature control and thus reduce the cost of production. The aim of this work was to isolate thermo-tolerant organisms from cassava peel and sawdust piles and to optimize cellulase production by the isolates. Out of 50 thermo-tolerant fungi isolated from cassava peels and sawdust piles, two isolates showed good potential for cellulase production and were molecularly identified using ribosomal DNA (rDNA) Internal Transcribed Spacer region (ITS) as Aspergillus fumigatus IB-A1 and Aspergillus fumigatus IB–Q1. The sequences were deposited in DNA Data Bank of Japan (DDBJ) and the European Molecular Biology Laboratory (EMBL). The two organisms, Aspergillus fumigatus IB- A1 and Aspergillus fumigatus IB- Q1 were assigned accession numbers of LC592224 and LC592225 respectively. Endoglucanase, β-glucosidase and exoglucanase production by Aspergillus fumigatus LC592224 was optimized in terms of the initial pH, nitrogen sources, and addition of inorganic salts. In a nutrient broth with peptone as the nitrogen source and at an initial pH of 5.5, the endoglucanase, β-glucosidase and exoglucanase activities were 1.404 ± 0.0789, 1.142 ± 0.09 and 0.828 ± 0.04 U/ml/min respectively after 120 h of cultivation. However, under the optimum culture conditions (pH of 6.0 in a medium containing NaNO3 and CaCl2), the endoglucanase, β-glucosidase and exoglucanase activities increased to 3.211 ± 0.029, 2.501 ± 0.072 and 1.834 ± 0.084 U/ml/min respectively. The results showed that under the optimum culture conditions, the activities of the enzymes are ranked as {endoglucanase} > {β-glucosidase}> {exoglucanase} (p < 0.05).