关键词: 巨大芽孢杆菌, 16S?rDNA, 低聚半乳糖 , 转糖基作用, β-半乳糖苷酶

Abstract: One bacterium strain producing βgalactosidase with transgalactosylation activity was screened from 97 strains of microorganisms stored in our laboratory using hydrolysis activity on o-nitrophenyl-β-D-galactopyranoside followed by transgalactosylation activity on lactose. Phenotypic analyses including morphology and physiology characteristics and 16S rDNA sequence analyses were carried out. The GenBank accession number of the 16S rDNA was DQ267829. By making a comprehensive view on all the results of taxonomy, the strain was identified as Bacillus megaterium 2-37-4-1. The growth condition for production of βgalactosidase of B. megaterium 2-37-4-1 was investigated. The optimal carbon source and nitrogen source were 1% lactose and 0.5 % peptone plus 0.5% yeast extract, respectively. High yield of the enzyme was obtained at 37℃ for 18 h. Effects of pH, the concentration of lactose, reaction temperature and time on the enzymecatalyzed transgalactosylation activity were studied and the reaction products were analyzed by thin layer chromatography (TLC) and highperformance liquid chromatography (HPLC). In 50mM phosphate buffer (pH 7.5) containing 40% lactose, reacted at 55℃ with shaking for 24 h, the transgalactosylation product was composed of 25.68% galactooligosaccharides (GOS), 33.02% disaccharides including lactose and transgalctosylated disaccharides, 26.37% glucose and 14.92% galactose.

Key words: galactooligosaccharides , ransgalactosylation, β-galactosidase, 16S rDNA, Bacillus megaterium