Expression of Bifidobacterium adolescentis beta-galactosidase in Bifidobacterium spp.

초록

To clone the β-gal genetic determinants of B. adolescentis INT-57, a cosmid gene library was constructed and screened in E. coli ER1458 for β-gal activity. A 7.2-kb Sal/Ⅰ DNA fragment expressing β-gal in E. coli was isolated, characterized by restriction mapping and cloned into the E. coli-Bifidobacterium shuttle vector pDG7. The derived plasmids pLA71 and pLA74, containing the insert in the opposite orientations, were transformed into Bifidobacterium strains belonging to 6 different species. B. animalis MB209, B. breve MB226, B. bifidum MB254 and B. longum MB260 presented very high levels of β-gal endogenous expression and no increase of activity was detected when transformed with pLA71 or pLA74. B. cuniculi and B. indicum strains presented low levels of endogenous β-gal, while pLA71 and pLA74 transformants showed a significant increase of activity. Respect to the controls, in B. cuniculi MB279, MB280 and MB281 harbouring pLA71 or pLA74, β-gal expression increased 2-3 fold, while 5 times higher β-gal levels were found in B. indicum MB101 transformants.