title: Induction of sucrose utilization genes from Bifidobacterium lactis by sucrose and raffinose.
abstract: The probiotic organism Bifidobacterium lactis was isolated from a yoghurt starter culture with the aim of analyzing its use of carbohydrates for the development of prebiotics. A sucrose utilization gene cluster of B. lactis was identified by complementation of a gene library in Escherichia coli. Three genes, encoding a sucrose phosphorylase (ScrP), a GalR-LacI-type transcriptional regulator (ScrR), and a sucrose transporter (ScrT), were identified by sequence analysis. The scrP gene was expressed constitutively from its own promoter in E. coli grown in complete medium, and the strain hydrolyzed sucrose in a reaction that was dependent on the presence of phosphates. Primer extension experiments with scrP performed by using RNA isolated from B. lactis identified the transcriptional start site 102 bp upstream of the ATG start codon, immediately adjacent to a palindromic sequence resembling a regulator binding site. In B. lactis, total sucrase activity was induced by the presence of sucrose, raffinose, or oligofructose in the culture medium and was repressed by glucose. RNA analysis of the scrP, scrR, and scrT genes in B. lactis indicated that expression of these genes was influenced by transcriptional regulation and that all three genes were similarly induced by sucrose and raffinose and repressed by glucose. Analysis of the sucrase activities of deletion constructs in heterologous E. coli indicated that ScrR functions as a positive regulator.
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, South Africa.
authors.forename: Marla I
authors.initials: MI
authors.lastname: Trindade
authors.forename: Valerie R
authors.initials: VR
authors.lastname: Abratt
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Reid
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001644:Bifidobacterium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005964:Glucosyltransferases / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D011887:Raffinose / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013393:Sucrase / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D013395:Sucrose; D005964:Glucosyltransferases; C025901:sucrose phosphorylase; D013393:Sucrase; D011887:Raffinose