Evaluation of agricultural wastes as a sustainable carbon source for the production of β-glucosidase from Bacillus stercoris, its purification and characterization

Abstract

β-glucosidases are found in all domains of life and has the ability to hydrolyse the glycosidic bond between carbohydrates and non-carbohydrates residues making it a potent enzyme from an industrial and agricultural perspective. The aim of the current study was isolation, screening, and identification of bacterial strains having maximum β-glucosidase activity from soil sample of Jacobabad, Pakistan. The isolates were screened primarily, and efficient isolates were confirmed for β-glucosidase production through secondary screening. Among the different isolated strains, 1j2 was selected as the best β-glucosidase producer. The isolate showed 99% similarity with Bacillus stercoris after 16S rRNA sequencing. Different culture conditions were optimized for effective β-glucosidase production. Enhanced level of β-glucosidase was achieved at 40°C, pH 8 at 150 rpm in a β-glucosidase production medium supplemented with a combination of agricultural residues of wheat bran 0.25% (w/v) and orange peel 0.25% (w/v), using 5% inoculum. Bacillus stercoris produced a higher yield (2.89U/mg) of β-glucosidase under optimized conditions. Partial purification of β-glucosidase was achieved after 80% ammonium sulfate precipitation. The enzyme was purified and had shown maximum specific activity of 53.2 U/mg with molecular weight of approximately 36 kDa. In all the tested metals Cu2+ was observed to have inhibitory effect while Ca2+ had not affected the enzyme activity significantly. While organic solvents and surfactants had significantly reduced the β-glucosidase activity. Based on the afore mentioned abilities of purified β-glucosidase from Bacillus stercoris strain it could be a promising player for the industrial applications of lignocellulose hydrolysis found in agricultural residues for the cheap production of biofuels.