Recombinant beta-galactosidase derived from Enterobacter cloacae Zjut HJ2001 for efficient biotransformation of galactooligosaccharides

Galactooligosaccharides (GOS), as a type of prebiotics, have excellent physical and chemical properties, and can be widely used in the pharmaceutical and food fields. Recently, the microbial β-galactosidases have gained widespread attentions in industrial GOS production. However, most β-galactosidases from microorganisms have low transgalactosylation activity, resulting in poor GOS yield of enzymatic transformation from lactose. In this paper, a brand new β-galactosidase derived from Enterobacter cloacae Zjut HJ2001 was screened out from soil, and successfully overexpressed, characterized, and mutated by combinatorial alanine-scanning and site-saturation mutagenesis. Compared to the yield of 51.73 % obtained by wild-type β-galactosidase with lactose concentration of 380 g/L, the obtained mutant β-gal-H542V achieved a higher GOS yield of 67.08 %, which was the highest in the reported literature. These results suggested that the developed mutagenesis strategy could improve the transgalactosylation efficiency, and the mutant β-gal-H542V could be regarded as a prospective biocatalyst for GOS industrial manufacturing.