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Induction of Cellulase Biosynthesis by Cellobiose Octaacetate in Aspergillus Humicola

Meher Nigad Nipa
Department of Microbiology, University of Chittagong, Chittagong 4331, Bangladesh

Sharmin Sultana
Department of Microbiology, University of Chittagong, Chittagong 4331, Bangladesh

M Abdul Hakim
Department of Microbiology, University of Chittagong, Chittagong 4331, Bangladesh

Abstract/ Executive Summary:

Aspergillus humicola, one of the major cellulase-producing fungi, was used in this study for carboxymethylcellulase (CMCase) production using Winstead’s basal broth supplanted with cellobiose octaacetate (COA), a synthetic carbon source. Under all conditions, the enzyme biosynthesis was remarkably increased when the inducer COA was added to the production medium containing carboxymethylcellulose (CMC). Maximum enzyme production (1.62 U/ml) was achieved in COA-containing at 37°C. The enzyme production was highest at initial pH 5.5 and after 7 days incubation. The enzyme exhibited maximum activity at 40°C with a reaction pH 5.5. CMCase activity was inhibited by its own substrate CMC at concentration higher than 1.0%. The study clearly demonstrated that COA is a good inducer for extracellular CMCase production by the fungus.

Keywords: Aspergillus humicola, Carboxymethylcellulase (CMCase), Carboxymethylcellulose (CMC), Cellobiose octaacetate (COA)

Location: Department of Microbiology, University of Chittagong, Chittagong

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Fortified food

Objectives:

1. The present study was attempted to evaluate the influence of cellobiose octaacetate (COA) on the inductive formation of cellulase production by the fungus under different cultural conditions, and also to determine the optimum conditions for the enzyme activity.

Methodology:

A potential cellulolytic fungal isolate, Aspergillus humicola, was isolated from the wheat straw and was maintained on Czapek’s and potato dextrose agar media. The fungus was identified according to taxonomical criteria. Primarily, the isolate was screened for the cellulolytic activity using plate clearing assay method on Winstead’s agar medium containing 1.2% CMC. Induction of cellulase by cellobiose octaacetate (COA) was performed in 100-ml conical flask containing 50 ml Winstead’s broth medium and 1.2% CMC supplemented with or without the inducer COA (0.6%). Each flask was inoculated with 3-days-old fungal culture, and was incubated for 72 h at 27°C for cellulase production. The fungal culture was filtered through Whatman No.1 filter paper and the filtrate was then centrifuged at 8,000 rpm for 15 min. The clear supernatant was recovered and stored at 4°C with few drops of sodium azide to avoid contamination. The optimum cultural conditions, such as incubation period, initial pH and incubation temperature, for production of cellulase in shake-flask culture were determined. Cellulase (CMCase) activity was assayed using 1.0% (w/v) solution of carboxymethylcellulose (CMC) in 0.1 M citrate buffer (pH 4.6) as substrate. The reaction mixture (5 ml), containing 2.0 ml substrate, 2.0 ml enzyme solution and 1.0 ml citrate buffer (0.1 M), was incubated at 35^oC for 120 min. The reducing sugars released were measured as glucose equivalents. One unit (U) of enzyme activity was defined as 1 μmol of reducing sugar released, as glucose equivalent, in 1 min under the assay conditions. Effect of substrate (CMC) concentration (0.1-2.0%), incubation temperature (35°- 60°C) and assay pH (3.5-6.0) on cellulase activity was determined.

Source of Information: Bangladesh J Microbiol, Volume 23, Number 2, December 2006, pp 174-176

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The present study clearly shows that the synthetic substrate, cellobiose octaacetate (COA) has the ability to induce cellulase production by A. humicola. Therefore, it could be incorporated in production medium for increased production of cellulase by the fungus. The fungus merits further attention as a potential source of extracellular cellulolytic enzymes.

Knowledge Management: Journal