title: Coexpression of β-D-galactosidase and L-arabinose isomerase in the production of D-tagatose: a functional sweetener.
abstract: The functional sweetener, d-tagatose, is commonly transformed from galactose by l-arabinose isomerase. To make use of a much cheaper starting material, lactose, hydrolization, and isomerization are required to take place collaboratively. Therefore, a single-step method involving β-d-galactosidase was explored for d-tagatose production. The two vital genes, β-d-galactosidase gene (lacZ) and l-arabinose isomerase mutant gene (araA') were extracted separately from Escherichia coli strains and incorporated into E. coli simultaneously. This gave us E. coli-ZY, a recombinant producing strain capable of coexpressing the two key enzymes. The resulted cells exhibited maximum d-tagatose producing activity at 34 °C and pH 6.5 and in the presence of borate, 10 mM Fe(2+), and 1 mM Mn(2+). Further monitoring showed that the recombinant cells could hydrolyze more than 95% lactose and convert 43% d-galactose into d-tagatose. This research has verified the feasibility of single-step d-tagatose fermentation, thereby laying down the foundation for industrial usage of lactose.
authors.affiliation: State Key Laboratory of Materials-Oriented Chemical Engineering, College of Food Science and Light Industry, Nanjing University of Technology , 30 Puzhu South Road, Nanjing 211816, People's Republic of China.
authors.forename: Yijing
authors.initials: Y
authors.lastname: Zhan
authors.forename: Zheng
authors.initials: Z
authors.lastname: Xu
authors.forename: Sha
authors.initials: S
authors.lastname: Li
authors.forename: Xiaoliu
authors.initials: X
authors.lastname: Liu
authors.forename: Lu
authors.initials: L
authors.lastname: Xu
authors.forename: Xiaohai
authors.initials: X
authors.lastname: Feng
authors.forename: Hong
authors.initials: H
authors.lastname: Xu
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001711:Biotransformation; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D006601:Hexoses / Q000737:chemistry / Q000378:metabolism*; D007218:Industrial Microbiology; D007785:Lactose / Q000737:chemistry / Q000378:metabolism*; D013549:Sweetening Agents / Q000737:chemistry*; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D006601:Hexoses; D013549:Sweetening Agents; D001616:beta-Galactosidase; D019747:Aldose-Ketose Isomerases; C019715:L-arabinose isomerase; D007785:Lactose; C030192:tagatose