EXTRACTION AND CHARACTERIZATION OF CELLULASE FROM FOREST AND COMPOST SOIL FUNGAL ISOLATES AND EVALUATION OF ITS APPLICATION FOR DEGRADATION OF FINGER MILLET AND OAT STRAW

Abstract

Cellulases are complex hydrolytic enzymes working synergistically on the hydrolysis of cellulose to produce smaller sugar components including glucose units. These enzymes have tremendous environmental, industrial and agricultural applications including enhancement of the degradability of lignocellulosic materials. In this research fungal isolates were isolated from forest and compost soil samples and allowed to produce cellulases; and the extent to which the cellulases enhance the degradability of finger millet and oat straw was evaluated. A total of 53 fungal isolates were isolated from forest and compost soil samples. Further screening of the isolates on 1% carboxymethyl cellulose media resulted in 21(40%) cellulolytic fungal species. Out of which, six were selected as efficient cellulolytic fungi and eventually subjected for identification. These isolates belonged to the genera Trichoderma, Aspergillus and Penicillium on the basis of their morphological characteristics. Cultivation of the fungal isolates for cellulase production using Submerged fermentation and Solid-state fermentation was assayed at different growth conditions. Assay for cellulase activity was carried out using Carboxymethyl cellulose (for CMCase/endoglucanase) and Filter paper (for FPase”/ total cellulase) activity. The results showed that the highest cellulase production (46.52±0.44U/dL CMCase and 41.57±0.39 FPU/dL FPase) from SmF was obtained at pH of 5.5. Although, a fungal isolate designated as FSI6 (isolated from forest soil sample) showed maximum CMCase production (83.12 ± 3.18 U/dL) and FPase (44.51± 0.391FPU/dL) in FMS supplemented SSF at 280C and a pH of 6. All compost soil isolates showed better cellulase production in SSF at 380C and a pH of 5 than forest soil isolates. For instance, the fungal isolate designated as CSI3 (isolated from compost soil sample) showed maximum CMCase stability (48.37 ± 0.27U/dL) at 600C and a pH of 5. Partial characterization of the cellulases from the six isolates exhibited differences in terms of temperature, pH and metallic ion effects. The effect of pH and temperature on the activity and stability of cellulase indicated that as the temperature and pH increased, cellulase activity also increased while a further increase beyond the highest values revealed a decrease in activity. More than 50% residual activity of cellulase was obtained at temperatures 50 and 60°C incubated for 30min for all six isolates. On the other hand, the effect of metallic ions (Ca2+, Na+, Co2+, Mg2+ and Fe2+ ) on cellulase activity showed that three of the ions i.e. Mg2+, Co2+ and Ca2+ decreased the activity while Fe2+ enhanced the same as the concentration increased. The percentage saccharification on finger millet (28.9%) was higher than that of oat straw. The findings generally suggest that the isolates had high potential for production of cellulase which can be used in the improvement of degradation of cellulosic biomasses.