title: Polymorphism and selection of rpoS in pathogenic Escherichia coli.
abstract: BACKGROUND
  Though RpoS is important for survival of pathogenic Escherichia coli in natural environments, polymorphism in the rpoS gene is common. However, the causes of this polymorphism and consequential physiological effects on gene expression in pathogenic strains are not fully understood.
  
  
  RESULTS
  In this study, we found that growth on non-preferred carbon sources can efficiently select for loss of RpoS in seven of ten representative verocytotoxin-producing E. coli (VTEC) strains. Mutants (Suc++) forming large colonies on succinate were isolated at a frequency of 10-8 mutants per cell plated. Strain O157:H7 EDL933 yielded mainly mutants (about 90%) that were impaired in catalase expression, suggesting the loss of RpoS function. As expected, inactivating mutations in rpoS sequence were identified in these mutants. Expression of two pathogenicity-related phenotypes, cell adherence and RDAR (red dry and rough) morphotype, were also attenuated, indicating positive control by RpoS. For the other Suc++ mutants (10%) that were catalase positive, no mutation in rpoS was detected.
  
  
  CONCLUSIONS
  The selection for loss of RpoS on poor carbon sources is also operant in most pathogenic strains, and thus is likely responsible for the occurrence of rpoS polymorphisms among E. coli isolates.
authors.affiliation: Department of Biology, Life Sciences Building, Rm, 433, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4K1, Canada. dongt2@mcmaster.ca
authors.forename: Tao
authors.initials: T
authors.lastname: Dong
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Chiang
authors.forename: Charlie
authors.initials: C
authors.lastname: Joyce
authors.forename: Rosemary
authors.initials: R
authors.lastname: Yu
authors.forename: Herb E
authors.initials: HE
authors.lastname: Schellhorn
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D002460:Cell Line; D004269:DNA, Bacterial / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D016296:Mutagenesis; D010641:Phenotype; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion; D054323:Shiga-Toxigenic Escherichia coli / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism / Q000472:pathogenicity; D012808:Sigma Factor / Q000235:genetics*; D019802:Succinic Acid / Q000378:metabolism; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D019802:Succinic Acid