Characterization of a GH5 β-1, 4-endo-glucanase from Bacillus subtilis ZS57 and its potential application in brewing industry and agricultural straws saccharification

To evaluate a novel β-1, 4-endo-glucanase, BsEgl5A, from the bacterium Bacillus subtilis ZS57 isolated from forest soil. The β-1, 4-endo-glucanase (BsEgl5A) gene was cloned and heterogeneously expressed in Escherichia coli. BsEgl5A contained a catalytic domain of glycoside hydrolase family 5 and shared 71% identity with β-1, 4-endo-glucanase from Bacillus sp. IARI-SP-4. The purified endoglucanase had a molecular weight of 55 kDa, as estimated by SDS-PAGE and western blotting. The enzyme exhibited maximum activity at 55℃ and pH 5.0, and showed remarkable stability at 70℃ and pH 3.0-7.0. The activity of BsEgl5A was improved by Mn²⁺ ions and inhibited in the presence of Cu²⁺ ions. BsEgl5A was highly active towards laminarin and barley β-glucan, moderately towards CMC-Na. BsEgl5A degraded cellotetrose, cellopentose and cellohexaose to cellotriose and cellobiose. Moreover, BsEgl5A reduced both the filtration time and the viscosity of the brewer mash. Among tested agricultural straws, BsEgl5A showed highest reducing sugars production (3.54 mg/mL) with corn straw. These characteristics make BsEgl5A as useful candidate for degradation of plant biomass to simple sugars in brewing industry and biofuel production.