Abstract
Cellulolytic bacteria were isolated and screened from municipal solid wastes and rice straw wastes using Carboxy Methyl Cellulose (CMC) agar medium as a selective medium. Production of clear zones by the bacterial isolates on CMC agar medium supplemented with 1% CMC was considered as indicative of extracellular cellulase activity. The size of transparent zone diameter was considered as proportional to the level of cellulase production. These bacterial isolates were identified as Bacillus sp., Pseudomonas sp. and Serratia sp. based on morphological, cultural and biochemical characteristics. A basal medium containing CMC, KH2PO4, K2HPO4, MgSO4, (NH4)2SO4, CaCl2 and FeSO4 at pH 7.0 was used for cellulase production. The assay of cellulase in term of CMCase was performed by measuring the release of reducing sugar. Different physicochemical parameters were optimized for cellulase production at shake flask fermentation. Time course study revealed that maximum level of cellulase was produced by Bacillus and Serratia isolates after 24 h of cultivation and by Pseudomonas isolates after 42 h of cultivation. Optimum level of cellulase was produced by Pseudomonas and Bacillus isolates at 37°C, and that by Serratia isolate was at 35°C. Optimum pH for cellulase production by these bacterial isolates was 7.0. Optimum temperature and pH for the activity of cellulase from these isolates were 40°C and 7.0, respectively. The cellulase from these isolates was found almost stable up to 55°C and at pH 7.0 for 1 h. The crude cellulase could liberate reducing sugar from filter paper through hydrolysis. Results showed that bacterial isolates produced significant level of cellulase with cellulose degrading capability.
Highlights
Cellulose and hemicelluloses are the most abundant biomasses on the earth and have the greatest potential to resolve both the energetic and environmental demands of bioenergy [1,2]
Based on the biochemical tests, morphological and cultural characteristics, isolate MSW3 was identified as Bacillus sp., isolate PA1 was identified as Serratia sp. and isolates RSW3 and PA2 were identified as Pseudomonas spp
Bacterial cell growth was observed by counting the colony forming units, the results indicate that cellulase production was growth associated (Figure 2)
Summary
Cellulose and hemicelluloses are the most abundant biomasses on the earth and have the greatest potential to resolve both the energetic and environmental demands of bioenergy [1,2]. Cellulases are inducible enzymes synthesized by a large diversity of microorganisms including both fungi and bacteria during their growth on cellulosic materials. The most important use of cellulase is in the bioconversion of plant based cellulosic and lignocellulosic waste, which opens the possibility of virtually inexhaustible and unique source of renewable biofuel [4,18,19]. Nowadays, these enzymes account for approximately 20% of the world enzyme market used on industrial basis [6]
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