Asian Journal of Microbiology, Biotechnology & Environmental Sciences Paper

OPTIMIZATION OF CULTURAL CONDITIONS FOR CELLULASE PRODUCTION BY CELLULOLYTIC FUNGAL ORGANISMS AS THEY RELATE TO RESIDUAL SUGAR YIELD IN BROTH MEDIUM

F.D. OTAJEVWO AND I.N. IBEH

Abstract

One hundred and fifteen samples made of 42 (36.5%) rumen fluid, 36 (31.3%) cowdung and 37 (32.2%) soil samples were used for the study. Rumen liquor was collected by use of stomach tubes inserted into the mouths of cows and by suction, liquor was collected into prewarmed thermoflasks under continuous flushing with carbondioxide. Cowdung samples were obtained with the aid of sterile swab sticks. Soil samples were collected into sterile universal containers. All samples were obtained from abattoirs situated at three locations in Benin City, Nigeria. Samples were investigated for cellulolytic fungi by Filter Paper Yeast Mineral broth method. Cellulase production was assayed by Carboxymethyl cellulose broth method while residual sugar yield and other cellulolytic activities were determined by 3, 5-Dinitrosalicylic acid, Filter paper, Microcrystalline and Viscometric methods. Cellulolytic fungal organisms isolated included Trichoderma reesei, Rhizopus stolonifer, Penicillium iriensis, Aspergillus fumigates, Aspergillus flavus, Aspergillus niger, Rhizopus ch+-inensis, Penicillium oxalicium, Trichoderma virens, Fusarium solani and Geotrichum candidum. Eight (53.3%), 3 (20.0%) and 4 (26.7%) of these organisms were isolated from soil, rumen fluid and cowdung respectively. The highest cellulase producing isolate was Aspergillus fumigates and the least was Trichoderma reesei. Total cellulase yield by all organisms was 14.74 ± 1.2 IU/mL. Individual and collective yield was high compared to reports of earlier studies. Residual sugar was optimally secreted into broth medium at 40oC and pH 5 by all isolates. The lowest sugar yields were obtained at 500C, pH 6. Cellulolytic indices (residual sugar yield, exoglucanase activity, endoglucanase activity, extracellular protein yield and percentage loss of viscosity of carboxymethyl cellulose) of all isolates peaked at 38 ± 0.70C and pH 5 ± 0.2 although there was no significant difference in the individual recorded values (P>0.05). Optimal pH and temperature for individual isolates were slightly different i.e., 340C and pH 4.5 were optimal for Aspergillus fumigatus. The significance and implications of these are highlighted.