title: Growth-phase-dependent expression of the operon coding for the glycosylated autotransporter adhesin AIDA-I of pathogenic Escherichia coli.
abstract: The adhesin involved in diffuse adherence (AIDA-I) is an autotransporter found in pathogenic strains of Escherichia coli causing diarrhea in humans and pigs. The AIDA-I protein is glycosylated by a specific enzyme, the AIDA-associated heptosyltransferase (Aah). The aah gene is immediately upstream of the aidA gene, suggesting that they form an operon. However, the mechanisms of regulation of the aah and aidA genes are unknown. Using a clinical E. coli isolate expressing AIDA-I, we identified two putative promoters 149 and 128 nucleotides upstream of aah. Using qRT-PCR, we observed that aah and aidA are transcribed in a growth-dependent fashion, mainly at the start of the stationary phase. Western blotting confirmed that protein expression follows the same pattern. Using a fusion to a reporter gene, we observed that the regulation of the isolated aah promoter matched this transcription and expression pattern. Lastly, we found glucose to be a repressor and nutrient starvation to be an inducer. Taken together, our results suggest that, in the strain and the conditions we studied, aah-aidA is transcribed as a bicistronic message from a promoter upstream of aah, with maximal expression under conditions of nutrient limitation such as high cell density.
authors.affiliation: Department of Bacterial Animal Diseases, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC, Canada.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Berthiaume
authors.forename: Marie-Florence
authors.initials: MF
authors.lastname: Leblond
authors.forename: Josée
authors.initials: J
authors.lastname: Harel
authors.forename: Michael
authors.initials: M
authors.lastname: Mourez
mesh_terms: D018830:Adhesins, Escherichia coli / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006031:Glycosylation; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic
chemical_list: C075559:AIDA-I protein, E coli; D018830:Adhesins, Escherichia coli; D029968:Escherichia coli Proteins; D016695:Glycosyltransferases; C433803:autotransporter-adhesin-heptosyltransferase, E coli