Selection of Bacillus subtilis strains capable of producing β-glucanase supporting the hydrolysis of yeast cell walls

Abstract

The selection of B. subtilis strains was carried out with 15 strains from the collections of the Vietnam National University of Agriculture and the University of Economic and Technical Industries, Hanoi, Vietnam. To investigate the specific ability of β-glucanase in supporting the hydrolysis of beer yeast cells, CMC substrates in enzyme-activated test media of traditional methods was replaced by yeast cell walls in this study. The B. subtilis strains were activated on Nutrient Broth culture and then transplanted into MT3 culture for producing β-glucanase. Optical density (OD_600nm) measurement was used to estimate the bacterial density. The β-glucanase activity formed by bacteria cells free supernatant was quantified by agar diffusion method on the enzyme-activated test media MT4. Two B. Subtilis strains , BG21 and BG15, were selected based on their largest clear-zones on agar plates. By modifying the values of the affecting factors and keeping the remaining influencing factors unchanged, it was determined that the B. subtilis BG21 and BG15 strains produced the highest biomass at the conditions of the culture time of 24 and 28  h, at pH 7.0, and at 37^oC, respectively; furthermore, the highest activity of β-glucanase of the two strains BG21 and BG15 was exhibited at the culture time of 52 and 56 h, at pH 7.0, and at 37^oC, respectively.
Practical applications
Bacillus subtilis strains with the highest β-glucanase producing ability will be used for the production of biological products containing B. subtilis and β-glucanase which supports the hydrolysis of the beer yeast cells in the production of pig feed.