A novel cold-adapted phospho-beta-galactosidase from Bacillus velezensis and its potential application for lactose hydrolysis in milk

A phospho-beta-galactosidase gene (BsGal1332) was doned from Bacillus velezensis and successfully expressed in Escherichia coli BL21(DE3). The active BsGal1332 was identified to be a homodimer with a combined molecular mass of approximately 113 kDa, and it belonged to the glycoside hydrolase family 1.TheBsGal1332 displayed relative strict substrate specificity for galactosyl compounds compared with the other phospho-beta-galactosidases. The purified BsGal1332 showed the maximum activity at pH 8.0 and 50 degrees C for 2-nitrophenyl-beta-D-galactopyranoside (oNPGal) and at 40 degrees C for lactose. BsGal1332 was slightly activated by K+ and Na+, but not strongly affected by Ca2+, and was stable at pH 6.0-7.0 and 40 degrees C or below it. The activity of BsGal1332 decreased quickly after incubation at 50 degrees C or higher temperature, suggesting it was a cold-adapted enzyme. Moreover. BsGal1332 could hydrolyze lactose and oNPGaI with K-m values of 23.68 and 2.36 mM and k(cat) values of 11755 and 155.61 s(-1) at 4 degrees C. respectively. Additionally, 1 U of the BsGal1332 could thus be capable of hydrolyzing about 38% of the lactose in 1 mL of milk after incubating at 4 degrees C for 4 h. Taken together, these properties of BsGal1332 made it a new promising industrial biocatalyst for efficient lactose hydrolysis in milk. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

BsGal1332 is a cold-adapted enzyme with strict substrate specificity for galactosyl compounds, making it suitable for efficient lactose hydrolysis in dairy products.