title: Natural rpoS mutations contribute to population heterogeneity in Escherichia coli O157:H7 strains linked to the 2006 US spinach-associated outbreak.
abstract: We previously reported significantly different acid resistance between curli variants derived from the same Escherichia coli O157:H7 strain, although the curli fimbriae were not associated with this phenotypic divergence. Here we investigated the underlying molecular mechanism by examining the genes encoding the common transcriptional regulators of curli biogenesis and acid resistance. rpoS null mutations were detected in all curli-expressing variants of the 2006 spinach-associated outbreak strains, whereas a wild-type rpoS was present in all curli-deficient variants. Consequently curli-expressing variants were much more sensitive to various stress challenges than curli-deficient variants. This loss of general stress fitness appeared solely to be the result of rpoS mutation since the stress resistances could be restored in curli-expressing variants by a functional rpoS. Comparative transcriptomic analyses between the curli variants revealed a large number of differentially expressed genes, characterized by the enhanced expression of metabolic genes in curli-expressing variants, but a marked decrease in transcription of genes related to stress resistances. Unlike the curli-expressing variants of the 1993 US hamburger-associated outbreak strains (Applied Environmental Microbiology 78: 7706-7719), all curli-expressing variants of the 2006 spinach-associated outbreak strains carry a functional rcsB gene, suggesting an alternative mechanism governing intra-strain phenotypic divergence in E. coli O157:H7.
authors.affiliation: Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, CA, USA. Electronic address: michelle.carter@ars.usda.gov.
authors.forename: Michelle Qiu
authors.initials: MQ
authors.lastname: Carter
authors.affiliation: Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, CA, USA.
authors.forename: Jacqueline W
authors.initials: JW
authors.lastname: Louie
authors.affiliation: Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, CA, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Huynh
authors.affiliation: Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, CA, USA.
authors.forename: Craig T
authors.initials: CT
authors.lastname: Parker
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004196:Disease Outbreaks; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D005506:Food Contamination; D005517:Foodborne Diseases / Q000453:epidemiology / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D009154:Mutation; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D018724:Spinacia oleracea / Q000382:microbiology*; D014481:United States / Q000453:epidemiology
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria
keywords: Curli; Escherichia coli O157:H7; Population heterogeneity; Stress fitness; Transcriptomic; rpoS