Abstract
Rice straw is a major agricultural waste that can be used as an alternative substrate to expensive raw materials for endoglucanases (CMCase) production by microorganisms. This study aimed to search for a microorganism having the potential to produce endoglucanase from rice straw. From compost samples, 40 bacterial colonies were isolated on carboxymethylcellulose (CMC) agar. Among them, 16 isolates showed a hydrolysis zone on a CMC agar plate with hydrolysis (HC) values ranging from 1.15±0.02 to 4.40±0.52. Based on hydrolysis zone diameter and HC value, isolates CP1, CP2 and CP3 were further examined for their CMCase production in CMC broth. According to CMCase production and stability, isolate CP1 was selected for further study. The optimal pH and temperature for CMCase production of isolate CP1 were 5 and 45 °C, respectively. When using pre-treated rice straw as a substrate for semi-solid-state fermentation, the highest CMCase activity of 0.142 ± 0.008 U/mL was obtained in a medium containing pre-treated rice straw of 60 g/L. The sequence alignment analysis and phylogenetic analysis suggested that the isolate CP1 was likely to be Streptomyces thermocoprophilus. The microorganism obtained from this study may be not only industrially important but also beneficial to the environment.
Highlights
Cellulase enzymes are a group of complex enzymes converting cellulose to glucose and other sugars
Cellobiohydrolases act at termini of cellulose and oligosaccharides produced by endoglucanases to convert them to cellobiose which is further digested by β-glucosidase to glucose
Various strains of actinomyces have been evaluated for their ability to degrade the lignocellulosic biomass, which can be potentially implemented in the lignocellulolytic enzymes production from different value-added products
Summary
Cellulase enzymes are a group of complex enzymes converting cellulose to glucose and other sugars. The cellulase enzymes comprise three major types of enzymes: endoglucanases (E.C. 3.2.1.4), exoglucanases, including cellobiohydrolases (CBHs) (E.C. 3.2.1.91) and β-glucosidase (E.C. 3.2.1.21).. Cellobiohydrolases act at termini of cellulose and oligosaccharides produced by endoglucanases to convert them to cellobiose which is further digested by β-glucosidase to glucose.. LCB conversion to bioethanol consists of four major steps including pretreatment, saccharification, fermentation and distillation.. Subsequent saccharification or hydrolysis is done by acids or enzymes to hydrolyze cellulose and hemicellulose into fermentable sugars (hexoses and pentoses). The enzymes required for efficient deconstruction of polysaccharides into monomeric sugars include modular and nonmodular glycosyl hydrolases (GHs) comprising of cellulases and hemicellulases, carbohydrate esterases (CEs), and auxiliary activity (AA) proteins.
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