Мolecular-genetic analysis of determinants encoding β-galactosidases of bacteria Bifidobacterium longum BIM B-813 D

The molecular-genetic analysis of the bacterial genome of the strain B. longum BIM B-813D distinguished by a high level of β-galactosidase production was performed. Genes Bgal_small_N, lacZ1, bgaB1, bgaB2 and bgaB3, and lacZ2, encoding the synthesis of β-galactosidases, were revealed in the deciphered genome. It was shown that the genes lacZ1, bgaB2, and bgaB3 characterized by an enhanced degree of similarity to the genes of closely related bifidobacterial species, presumably code for the enzymes catalyzing the specific reactions of hydrolysis and transglycosylation of carbohydrates. It was found that the enzymes BgaB1, BgaB2 and BgaB3 belong to the GH42 family of glycosyl hydrolases, whereas the enzymes LacZ1 and LacZ2 – to the GH2 family. The genome domains responsible for the synthesis of β-galactosidases in the strain B. longum BIM B-813D were studied in detail. A comparative analysis of the locus of lacZ1 in B. longum BIM B-813D and the similar genome fragment AS143_01230 from B. longum subsp. longum MC-42 detected the presence of the transposase gene ISL3 in the former strain. It was suggested that the insertion of the sequence of ISL3 in the lacZ1 locus resulted in the modified gene expression and the increased production of β-galactosidase in the strain B. longum BIM B-813D.