title: H-NS controls metabolism and stress tolerance in Escherichia coli O157:H7 that influence mouse passage.
abstract: BACKGROUND
  H-NS is a DNA-binding protein with central roles in gene regulation and nucleoid structuring in Escherichia coli. There are over 60 genes that are influenced by H-NS many of which are involved in metabolism. To determine the significance of H-NS-regulated genes in metabolism and stress tolerance, an hns mutant of E. coli O157:H7 was generated (hns::nptI, FRIK47001P) and its growth, metabolism, and gastrointestinal passage compared to the parent strain (43895) and strain FRIK47001P harboring pSC0061 which contains a functional hns and 90-bp upstream of the open-reading frame.
  
  
  RESULTS
  The hns mutant grew slower and was non-motile in comparison to the parent strain. Carbon and nitrogen metabolism was significantly altered in the hns mutant, which was incapable of utilizing 42 carbon, and 19 nitrogen sources that the parent strain metabolized. Among the non-metabolized substrates were several amino acids, organic acids, and key metabolic intermediates (i.e., pyruvate) that limit carbon acquisition and energy generation. Growth studies determined that the parent strain grew in LB containing 14 to 15% bile or bile salts, while the hns mutant grew in 6.5 and 9% of these compounds, respectively. Conversely, log-phase cells of the hns mutant were significantly (p < 0.05) more acid tolerant than the parent strain and hns mutant complemented with pSC0061. In mouse passage studies, the parent strain was recovered at a higher frequency (p < 0.01) than the hns mutant regardless of whether log- or stationary-phase phase cells were orally administered.
  
  
  CONCLUSIONS
  These results demonstrate that H-NS is a powerful regulator of carbon and nitrogen metabolism as well as tolerance to bile salts. It is likely that the metabolic impairments and/or the reduced bile tolerance of the E. coli O157:H7 hns mutant decreased its ability to survive passage through mice. Collectively, these results expand the influence of H-NS on carbon and nitrogen metabolism and highlight its role in the ability of O157:H7 strains to respond to changing nutrients and conditions encountered in the environment and its hosts.
authors.affiliation: Department of Food Hygiene and Technology, University of Ankara, Ankara, Turkey. Irfan.Erol@veterinary.ankara.edu.tr
authors.forename: Irfan
authors.initials: I
authors.lastname: Erol
authors.forename: Kwang-Cheol
authors.initials: KC
authors.lastname: Jeong
authors.forename: David J
authors.initials: DJ
authors.lastname: Baumler
authors.forename: Boris
authors.initials: B
authors.lastname: Vykhodets
authors.forename: Sang Ho
authors.initials: SH
authors.lastname: Choi
authors.forename: Charles W
authors.initials: CW
authors.lastname: Kaspar
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001647:Bile Acids and Salts / Q000494:pharmacology; D002244:Carbon / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019453:Escherichia coli O157 / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D005243:Feces / Q000382:microbiology; D005744:Gastric Acid / Q000737:chemistry; D041981:Gastrointestinal Tract / Q000382:microbiology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D009154:Mutation / Q000235:genetics*; D009584:Nitrogen / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D012965:Sodium Chloride; D002244:Carbon; D005968:Glutamate Decarboxylase; D009584:Nitrogen