Abstract

A bacterial strain was isolated from homemade Cheongkookjang as a producer of the ${\beta}$-galactosidase, capable of hydrolyzing lactose to liberate galactose and glucose residues. The isolate YB-1105 has been identified as Bacillus licheniformis on the basis of its 16S rDNA sequence, morphology and biochemical properties. ${\beta}$-Galactosidase activity was detected in both the culture supernatant and the cell extract of B. licheniformis YB-1105. The enzymes of both fractions demonstrated maximum activity for hydrolysis of para-nitrophenyl-${\beta}$-D-galactopyranoside (pNP-${\beta}Gal$) under identical reaction conditions of pH 6.5 and $50^{\circ}C$. However, ${\beta}$-galactosidase activity from the culture filtrate was affected more than that from the cell free extract at acidic pHs and high temperatures. The hydrolyzing activity of both ${\beta}$-galactosidases for pNP-${\beta}Gal$ was dramatically decreased by the addition of low concentrations of galactose, but was only marginally decreased by high concentrations of glucose or mannose.

가정에서 제조된 청국장으로부터 lactose를 glucose와 galactose로 가수분해하는 ${\beta}$-galactosidase의 생산균을 분리하였다. 분리균 YB-1105는 형태적 특성, 생화학적 성질 및 16S rRNA 유전자 염기서열에 근거하여 Bacillus licheniformis로 확인되었다. B. licheniformis YB-1105의 배양상등액과 균체파쇄액에서 모두 ${\beta}$-galactosidase 활성이 관찰되었으며 이들은 모두 pH 6.5와 $50^{\circ}C$의 반응조건에서 paranitrophenyl-${\beta}$-D-galactopyranoside의 가수분해 활성이 최대로 나타났다. 그러나 균체파쇄상등액에 비해 배양상등액의 ${\beta}$-galactosidase 활성은 산성 pH와 고온에서 크게 영향을 받았다. 한편 두 분획의 가수분해 활성은 낮은 농도의 galactose에 의해도 급격하게 저해되었으나, glucose와 mannose는 고농도에 의해서는 약하게 저해를 받는 것으로 확인되었다.

Keywords

• Bacillus licheniformis;
• identification;
• ${\beta}$-galactosidase;
• property