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In vitro experimental evolution has taught us many lessons on the molecular bases of adaptation. To move towards more natural settings, evolution in the mice gut has been successfully performed. Yet, these experiments suffered from the use of laboratory strains as well as the use of axenic or streptomycin‐treated mice to maintain the inoculated strains. To circumvent these limitations, we conducted a one‐year experimental evolution in vivo using a natural isolate of E. coli, strain 536, in conditions mimicking as much as possible natural environment with mother‐to‐offspring microbiota transmission. Mice were then distributed in 24 independent cages and separated into two different diets: a regular one (chow diet, CD) and high‐fat and high‐sugar one (Western Diet, WD). Genome sequences revealed an early and rapid selection during the breastfeeding period that selected the constitutive expression of the well‐characterized lactose operon. E. coli was lost significantly more in CD than WD; however, we could not detect any genomic signature of selection, nor any diet specificities during the later part of the experiments. The apparently neutral evolution presumably due to low population size maintained nevertheless at high frequency the early selected mutations affecting lactose regulation. The rapid loss of lactose operon regulation challenges the idea that plastic gene expression is both optimal and stable in the wild. [ABSTRACT FROM AUTHOR]

Focuses on the secreted proteins and features of Escherichia coli strains that may contribute to the pathogenesis of uropathogenic urinary tract infections. Percentage of adult women who suffer symptoms of cystitis during their lifetime; Virulence factors synthesized by uropathogens; Mechanisms by which uropathogens promote infection.

Presents information on a study which analyzed the instability of pathogenicity islands (PAI) of the uropathogenic strain Escherichia coli 536 using island probing method. Isolation and characterization of PAI II 536; Methodology; Commentary.

The uropathogenic Escherichia coli strain 536 possesses two large, unstable DNA regions on its chromosome, which were termed pathogenicity islands (pais). Deletions of pais, which occur with relatively high frequency in vitro and In vivo, lead to avirulent mutants. The genetic determinants for production of haemolysin (Hiy) and P-related fimbriae (Prf) are located in one of these islands. Deletion of this pathogenicity island (paill) not only removes the hly- and prf-specific genes, but also represses S fimbriae (Sfa), although the sfa genes of this virulence factor are not located on paill. We have identified two regulatory genes, prfB and prff, of the prf gene cluster that are homologous to the sfa regulatory genes sfaB and sfaC, respectively. Mutations in sfaB and sfaC that inhibit transcription of the major fimbrial subunit gene sfaA were complemented by the homologous prf genes, suggesting communication between the two fimbrial gene clusters in the wild-type strain. Chromosomal mutagenesis of the two prf regulators in strain 536 repressed transcription of sfaA, detected by Northern hybridization and a chromosomal sfaA-lacZ fusion, in addition, haemagglutination assays measured a lower level of S fimbriae in these mutants. Expression of the cloned prf regulators in trans reversed the effect of the mutations; furthermore, constitutive expression of prfB or prfl could also overcome the repression of S fimbriae in a strain that had lost the pathogenicity islands. Virulence assays in mice established that the prf mutants were less virulent than the wild-type strain. The results demonstrate that cross-regulation of two unlinked virulence gene clusters together with the co-ordinate loss of large DNA regions significantly influences the virulence of an extraintestinal E. coli... [ABSTRACT FROM AUTHOR]

The uropathogenic Escherichia coli strain 536 (O6:K15:H31) carries two large chromosomal pathogenicity islands (Pais). Both Pais are flanked by tRNA genes. Spontaneous deletion of Pai II results in truncation of the leuXtRNA5Leu gene. This tRNA is required for the expression of type 1 fimbriae (Fim) and other virulence factors. Transcription of fimA, encoding the major type 1 fimbrial subunit is controlled by an invertable DNA switch. The inversion is catalysed by two recombinases, FimB and FimE. FimB is abie to turn the switch on, FimE only off. The fimB gene of strain 536 contains five TTG codons recognized by tRNA5Leu, fimE contains only two. It was proposed that turning on the fim switch requires efficient translation of FimB, in turn requiring tRNA5Leu. Strains in which the TTG codons in fimB were replaced with CTG codons at the wild-type locus were able to produce type 1 fimbriae in the absence of leuX, fimB transcription was influenced by the presence of leuX, but only slightly affected by the presence or absence of leuX codons in fimB. FimB translation was significantly higher from codon-repiaced fimB genes than that of wild-type fimB genes in various strain backgrounds. The fim switch was shown to be switched off in leuX- derivatives of E. coli 536, but could be found in the on position when the codon-altered fimB gene was exchanged into the chromosome of these strains. From these data, it is apparent that tRNA5Leu is required for efficient translation of FimB, in turn, leading to type 1 fimbrial expression. [ABSTRACT FROM AUTHOR]

The uropathogenic Escherichia coli strain 536 (O6:K15:H31) carries two unstable DNA regions on its chromosome which were termed pathogenicity islands (Pais). Both pathogenicity islands, Pai I and Pai II, are incorporated into tRNA specific loci: Pai I is located in the tRNA gene for selenocysteine (selC), and Pai II is integrated in the leucine-specific tRNA locus leuX. Mutant strain 536-21 has lost the two pathogenicity islands together with the intact tRNA genes. While 536 is a virulent strain, 536-21 has lost a number of properties, including in vivo virulence. In previous publications we reported that the genes coding for two haemolysins (hly I, hly II) and P-related fimbria (prf) are located on the Pais. In this paper, we demonstrate that the expression of other gene products influencing metabolic properties in addition to in vivo virulence are strongly dependent on the intact tRNA loci selC and leuX. In order to determine the influence of the two tRNAs on the expression of these properties, the genes selC and leuX were cloned from the genome of strain 536 and then introduced into the mutant 536-21. Our results clearly show that the seleno-cysteine-specific tRNA (tRNASec) directly influences the ability of the bacteria to grow under anaerobic conditions, because selenocysteine is part of the enzyme formate dehydrogenase (FDH) which is involved in mixed acid fermentation. The rare leucine-specific tRNA5Leu, encoded by leuX, influences a number of properties including type 1 fimbria production, flagellation and motility, production of enterobactin and serum resistance, and is also necessary for full in vivo virulence. While the tRNASec is directly involved in the production of FDHs, the leuX specific tRNAs5Leu appears to influence the expression of various factors through specific transcriptional or translational control mechanisms. [ABSTRACT FROM AUTHOR]