title: Extracellular secretion in Bacillus subtilis of a cytoplasmic thermostable beta-galactosidase from Geobacillus stearothermophilus.
abstract: beta-Galactosidase catalyzes the hydrolysis of beta-galactosides into monosaccharides and is widely used in dairy processing. This study reports the extracellular secretion of a cytoplasmic thermostable beta-galactosidase from Geobacillus stearothermophilus IAM11001 in Bacillus subtilis. This enzyme has potential applications in the dairy industry. It was not secreted in B. subtilis by mediation of 3 general secretory signal peptides, but was secreted extracellularly when it was fused to a twin-arginine signal peptide of B. subtilis phosphodiesterase. Defined and rich culture media were used for recombinant enzyme production, and the extracellular target enzymatic activity reached about 44% of the total enzymatic activity synthesized at 18 h of cultivation in Luria-Bertani medium. As a control of secretion, when the signal peptide coding sequence was absent from the N terminus of the target gene bgaB, the extracellular target enzymatic activity obtained under the same condition of cultivation accounted for less than 7% of the total enzymatic activity synthesized. Results also showed that coexpression of the B. subtilis proteins TatAd and TatCd was indispensable for the secretion of the target enzyme.
authors.affiliation: State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, P. R. China.
authors.forename: Y
authors.initials: Y
authors.lastname: Xia
authors.forename: J
authors.initials: J
authors.lastname: Zhao
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: F
authors.initials: F
authors.lastname: Tian
authors.forename: H P
authors.initials: HP
authors.lastname: Zhang
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: W
authors.initials: W
authors.lastname: Chen
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics; D003612:Dairying / Q000379:methods; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D021382:Protein Sorting Signals / Q000502:physiology; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism*
chemical_list: D021382:Protein Sorting Signals; D010727:Phosphoric Diester Hydrolases; D001616:beta-Galactosidase