Abstract
The cellulase activity of Bacillus subtilis AS3 was enhanced by optimizing the medium composition by statistical methods. The enzyme activity with unoptimised medium with carboxymethylcellulose (CMC) was 0.07 U/mL and that was significantly enhanced by CMC, peptone, and yeast extract using Placket-Burman design. The combined effects of these nutrients on cellulase activity were studied using 22 full factorial central composite design. The optimal levels of medium components determined were CMC (1.8%), peptone (0.8%), and yeast extract (0.479%). The maximum enzyme activity predicted by the model was 0.49 U/mL which was in good agreement with the experimental value 0.43 U/mL showing 6-fold increase as compared to unoptimised medium. The enzyme showed multisubstrate specificity, showing significantly higher activity with lichenan and β-glucan and lower activity with laminarin, hydroxyethylcellulose, and steam exploded bagasse. The optimised medium with lichenan or β-glucan showed 2.5- or 2.8-fold higher activity, respectively, at same concentration as of CMC.
Highlights
Cellulases (3.2.1.4) have a wide range of industrial applications such as textile, laundry, pulp and paper, fruit juice extraction, and animal feed additives as well as in bioethanol production [1]
The maximum enzyme activity predicted by the model was 0.49 U/mL which was in good agreement with the experimental value 0.43 U/mL showing 6-fold increase as compared to unoptimised medium
CMC, peptone, yeast extract, K2HPO4, and MnCl2·4H2O displayed a positive effect for enzyme production, whereas MgSO4·7H2O and FeSO4·7H2O had a negative effect on enzyme activity (Table 2)
Summary
Cellulases (3.2.1.4) have a wide range of industrial applications such as textile, laundry, pulp and paper, fruit juice extraction, and animal feed additives as well as in bioethanol production [1]. Cellulases from bacteria Bacillus, Clostridium, Cellulomonas, Thermomonospora, Ruminococcus, Bacteroides, Erwinia, Acetivibrio, and actinomycetes in particular Streptomyces species have been reported [3, 4]. Bacteria, due to their high natural diversity, faster growth have the capability to produce highly thermostable, alkali stable enzyme complement and may serve as highly potent sources of industrially important enzymes. The production of extracellular cellulase in microorganisms is significantly influenced by a number of factors such as temperature, pH, aeration [11], and medium constituents [12]. The traditional “one-variable-at-a-time approach” for medium optimisation disregards the complex interactions
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