title: Gene structure and transcriptional organization of the dnaK operon of Bifidobacterium breve UCC 2003 and application of the operon in bifidobacterial tracing.
abstract: The incorporation and delivery of bifidobacterial strains as probiotic components in many food preparations expose these microorganisms to a multitude of environmental insults, including heat and osmotic stresses. We characterized the dnaK gene region of Bifidobacterium breve UCC 2003. Sequence analysis of the dnaK locus revealed four genes with the organization dnaK-grpE-dnaJ-ORF1, whose deduced protein products display significant similarity to corresponding chaperones found in other bacteria. Northern hybridization and real-time LightCycler PCR analysis revealed that the transcription of the dnaK operon was strongly induced by osmotic shock but was not induced significantly by heat stress. A 4.4-kb polycistronic mRNA, which represented the transcript of the complete dnaK gene region, was detected. Many other small transcripts, which were assumed to have resulted from intensive processing or degradation of this polycistronic mRNA, were identified. The transcription start site of the dnaK operon was determined by primer extension. Phylogenetic analysis of the available bifidobacterial grpE and dnaK genes suggested that the evolutionary development of these genes has been similar. The phylogeny derived from the various bifidobacterial grpE and dnaK sequences is consistent with that derived from 16S rRNA. The use of these genes in bifidobacterial species as an alternative or complement to the 16S rRNA gene marker provides sequence signatures that allow a high level of discrimination between closely related species of this genus.
authors.affiliation: Alimentary Pharmabiotic Centre and Department of Microbiology, Bioscience Institute, National University of Ireland, Cork, Ireland. m.ventura@ucc.ie
authors.forename: Marco
authors.initials: M
authors.lastname: Ventura
authors.forename: Ralf
authors.initials: R
authors.lastname: Zink
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Fitzgerald
authors.forename: Douwe
authors.initials: D
authors.lastname: van Sinderen
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001644:Bifidobacterium / Q000145:classification / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D018869:Heat-Shock Response; D006358:Hot Temperature; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009876:Operon; D009997:Osmotic Pressure; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; D000251:Adenosine Triphosphatases