Characterization and overexpression of a glucanase from a newly isolated B. subtilis strain

Glucanases are enzymes that hydrolysis glucans which are the major cell wall components in cereals. A newly isolated bacteria, assigned as Bacillus subtilis HB2, produces a monomeric glucanase (GLU HB2) of a molecular mass of 75 kDa. GLU HB2 has an optimal activity at pH 5 and 55°C. It is extremely stable at a broad range of pH and temperature up to 65°C, in presence of 5 mM of CaCl₂. In order to overcome the enzymatic inhibition problem observed in wild-type strains, GluHB2 gene was integrated into the genome of B. subtilis HB2 and the recombinant strain was named HB2G. The correlation of glucanase production with bacterial growth shows that the level of expression of HB2G remains low and relatively comparable to the wild-type strain. But in terms of productivity, the HB2G strain is more productive throughout bacterial culture. This low production and growth of the recombinant strain can be attributed to the toxicity of the overexpression of the glucanase gene under a constitutive promoter.