title: Evolutionary silence of the acid chaperone protein HdeB in enterohemorrhagic Escherichia coli O157:H7.
abstract: The periplasmic chaperones HdeA and HdeB are known to be important for cell survival at low pH (pH < 3) in Escherichia coli and Shigella spp. Here we investigated the roles of HdeA and HdeB in the survival of various enterohemorrhagic E. coli (EHEC) following exposure to pH 2.0. Similar to K-12 strains, the acid protections conferred by HdeA and HdeB in EHEC O145 were significant: loss of HdeA and HdeB led to over 100- to 1,000-fold reductions in acid survival, depending on the growth condition of prechallenge cells. However, this protection was much less in E. coli O157:H7 strains. Deletion of hdeB did not affect the acid survival of cells, and deletion of hdeA led to less than a 5-fold decrease in survival. Sequence analysis of the hdeAB operon revealed a point mutation at the putative start codon of the hdeB gene in all 26 E. coli O157:H7 strains analyzed, which shifted the ATG start codon to ATA. This mutation correlated with the lack of HdeB in E. coli O157:H7; however, the plasmid-borne O157-hdeB was able to restore partially the acid resistance in an E. coli O145ΔhdeAB mutant, suggesting the potential function of O157-HdeB as an acid chaperone. We conclude that E. coli O157:H7 strains have evolved acid survival strategies independent of the HdeA/B chaperones and are more acid resistant than nonpathogenic K-12 for cells grown under nonfavorable culturing conditions such as in Luria-Bertani no-salt broth at 28°C. These results suggest a divergent evolution of acid resistance mechanisms within E. coli.
authors.affiliation: Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, California, USA. michelle.carter@ars.usda.gov
authors.forename: Michelle Q
authors.initials: MQ
authors.lastname: Carter
authors.forename: Jacqueline W
authors.initials: JW
authors.lastname: Louie
authors.forename: Clifton K
authors.initials: CK
authors.lastname: Fagerquist
authors.forename: Omar
authors.initials: O
authors.lastname: Sultan
authors.forename: William G
authors.initials: WG
authors.lastname: Miller
authors.forename: Robert E
authors.initials: RE
authors.lastname: Mandrell
mesh_terms: D000143:Acids / Q000633:toxicity*; D018387:Codon, Initiator; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D019143:Evolution, Molecular; D017353:Gene Deletion; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000187:drug effects*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D017354:Point Mutation; D017422:Sequence Analysis, DNA; D013312:Stress, Physiological
chemical_list: D000143:Acids; D018387:Codon, Initiator; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C084501:hdeA protein, E coli; C084502:hdeB protein, E coli