β-Galactosidase BMG without galactose and glucose inhibition: Secretory expression in Bacillus subtilis and for synthesis of oligosaccharide.

β-Galactosidases can catalyze the hydrolysis of lactose and the synthesis of galacto-oligosaccharides (GOS) from lactose. The catalytic activity of β-galactosidases is usually inhibited by galactose and glucose, which hampers the complete hydrolysis of lactose in food products. In this report, a β-galactosidase (denoted as BMG) from Bacillus megaterium YZ08 without the inhibition by galactose and glucose is the first to our knowledge reported. Efficient secretory expression of BMG was successfully achieved in Bacillus subtilis WB800. With the increasing of galactose and glucose, the activity of BMG dramatically enhanced. With addition of 0.6 M galactose or 1 M glucose, the initial activity to oNPG hydrolysis was increased by 2.1-fold and 4.3-fold, respectively. Moreover, the synthetic rate of galacto-oligosaccharides was enhanced by 1.1-fold and 1.9-fold with the addition of 0.7 M galactose or glucose, respectively. The GOS (278 g/L) from 600 g/L lactose by BMG were efficiently produced within 12 h, and the substrate lactose was completely used up. These results suggest that BMG shows a potential application in the food industry.