Beta-Galactosidase-Producing Thermophilic Bacterium, Thermus thermophilus KNOUC114: Identification of the Bacterium, Gene and Properties of Beta-Galactosidase

A Beta-galactosidase-producing bacterium, strain KNOUC114 isolated from a hot spring was identified, and its gene of Beta-galactosidase and properties of the enzyme were studied. The strain KNOUC114 showed typical properties of genus Thermus with phenotypic characteristics of rod-shape (0.2x3.5 um), Gram negative, non-motile, endospore not observed, forming yellow-pigmented colonies, growing aerobically and optimally at 68-70 oC. The strain could grow at the temperature above 80 oC, which is a typical characteristic of Thermus thermophilus. The main cellular fatty acids of KNOUC114 were isobranched-C17:00 and C15:00 fatty acids that are the predomonant acyl chains of the strains of genus Thermus. In pylogenetic analysis based on 16S rDNA sequence, the strain KNOUC114 was finally identified as Thermus thermophilus species, and named as Thermus thermophilus KNOUC114. The Beta-galactosidase gene of KNOUC114 (KNOUC114 Beta-gal) was cloned and expressed in Eschericia coli. KNOUC114 Beta-gal was composed of 1938bp encoding 645 a.a with deduced MW. of 72,784 dalton. The purified recombinant Beta-galactosidase of KNOUC114 (KNOUC114 Beta-gal) reacted optimally at pH 5.7 and 85 oC, possessed good activity at the pH of raw milk and the temperature of HTST for raw milk, and was stable at the temperature of HTST and at the pH of raw milk, meaning that KNOUC114 Beta-gal is suitable to be used for hydrolyzation of lactose in raw milk during HTST pasteurization of raw milk.