Isolation of endo-1,4-b-D-glucanase producing Bacillus subtilis sp. from fermented foods and enhanced enzyme production bydeveloping the mutant strain

Abstract

Cellulolytic bacteria living in food can be applied to microbial feed additives to improve fiber digestion in animal feeds. In this study, a cellulase-producing bacteria was isolated from salted clam and treated with physical or chemical agents to enhance their enzyme production. The bacteria was identified as a strain of Bacillus subtilis on the basis of 16S rRNA analysis. Endo-1,4-b-D-glucanase (endoglucanase) was produced by the wild type using 0.4% carboxy-methyl-cellulose as a carbon source with maximal activity (0.04 U/mL) after 24 h incubation. Insoluble cellulose and oat spelt xylan were also used as carbon sources for investigation of exoglucanase and xylanase, however, these enzymes were not found in the culture supernatant. Maximum endoglucanase activity of Bacillus subtilis sp. was measured at 50°C and pH 5, respectively. Then, the strain was subjected to classical mutagenesis (UV-irradiation and chemical treatment) to improve endoglucanase production. A mutant strain, P11 treated with ethyl methyl sulfonate was finally selected. Mutant P11 was sub-cultured and tested for endoglucanase production, which was 0.05 U/mL after 24 h growth. The significant difference of endoglucanase production between wild type and mutant P11 was prolonged to 10th generation. Thus, the mutant strain was found to have enhanced endoglucanase production.