• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.469-478
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• 2015

In spite of the reported probiotic effects, Bifidobacterium bifidum BGN4 (BGN4) showed no βglucosidase activity and failed to biotransform isoflavone glucosides into the more bioactive aglycones during soy milk fermentation. To develop an isoflavone-biotransforming BGN4, we constructed the recombinant B. bifidum BGN4 strain (B919G) by cloning the structural β-glucosidase gene from B. lactis AD011 (AD011) using the expression vector with the constitutively active promoter 919 from BGN4. As a result, B919G highly expressed β-glucosidase and showed higher β-glucosidase activity and heat stability than the source strain of the β-glucosidase gene, AD011. The biotransformation of daidzin and genistin compounds using the crude enzyme extract from B919G was completed within 4 h, and the bioconversion of daidzin and genistin in soy milk during fermentation with B919G also occurred within 6 h, which was much faster and higher than with AD011. The incorporation of this β-glucosidase-producing Bifidobacterium strain in soy milk could lead to the production of fermented soy milk with an elevated amount of bioavailable forms of isoflavones as well as to the indigenous probiotic effects of the Bifidobacterium strain.

• Journal of Microbiology and Biotechnology
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• v.29 no.11
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• pp.1717-1728
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• 2019

The gene encoding β-galactosidase was cloned from Bifidobacterium longum RD47 with combinations of several bifidobacterial promoters, and expressed in B. bifidum BGN4. Among the recombinant bifidobacteria, BGN4+G1 showed the highest β-galactosidase level, for which the hydrolytic activity was continuously 2.5 to 4.2 times higher than that of BGN4 and 4.3 to 9.6 times higher than that of RD47. The β-galactosidase activity of BGN4+G1 was exceedingly superior to that of any of the other 35 lactic acid bacteria. When commercial whole milk and BGN4+G1 were reacted, BGN4+G1 removed nearly 50% of the lactose in the milk by the 63-h time point, and a final 61% at 93 h. These figures are about twice the lactose removal rate of conventional fermented milk. As for the reaction of commercial whole milk and crude enzyme extract from BGN4+G1, the β-galactosidase of BGN4+G1 eliminated 51% of the lactose in milk in 2 h. As shown below, we also compared the strengths and characteristics of the strong bifidobacterial promoters reported by previous studies.

• Journal of Microbiology and Biotechnology
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• v.22 no.12
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• pp.1714-1723
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• 2012

${\beta}$-Glucosidase is necessary for the bioconversion of glycosidic phytochemicals in food. Two Bifidobacterium strains (Bifidobacterium animalis subsp. lactis SH5 and B. animalis subsp. lactis RD68) with relatively high ${\beta}$-glucosidase activities were selected among 46 lactic acid bacteria. A ${\beta}$-glucosidase gene (bbg572) from B. lactis was shotgun cloned, fully sequenced, and analyzed for its transcription start site, structural gene, and deduced transcriptional terminator. The structural gene of bbg572 was 1,383 bp. Based on amino sequence similarities, bbg572 was assigned to family 1 of the glycosyl hydrolases. To overexpress bbg572 in Bifidobacterium, several bifidobacteria expression vectors were constructed by combining several promoters and a terminator sequence from different bifidobacteria. The maximum activity of recombinant Bbg572 was achieved when it was expressed under its own promoter and terminator. Its enzyme activity increased 31-fold compared with those of its parental strains. The optimal pH for Bbg572 was pH 6.0. Bbg572 was stable at $37-40^{\circ}C$. It hydrolyzed isoflavones, quercetins, and disaccharides with various ${\beta}$-glucoside linkages. Bbg572 also converted the ginsenosides Rb1 and Rb2. These results suggest that this new ${\beta}$-glucosidase-positive Bifidobacterium transformant can be utilized for the production of specific aglycone products.