Distribution of chromosome length variation in natural isolates of Escherichia coli

The Tat system translocates folded proteins across energy-transducing prokaryotic membranes. In the bacterial model system Escherichia coli, the three components TatA, TatB, and TatC assemble to functional translocons. TatA and TatB both possess an N-terminal transmembrane helix (TMH) that is followed by an amphipathic helix (APH). The TMHs of TatA and TatB generate a hydrophobic mismatch with only 12 consecutive hydrophobic residues that span the membrane. We shortened or extended this stretch of hydrophobic residues in either TatA, TatB, or both, and analyzed effects on transport functionality and translocon assembly. The wild type length functioned best but was not an absolute requirement, as some variation was tolerated. Length-variation in TatB clearly destabilized TatBC-containing complexes, indicating that the 12-residues-length is crucial for Tat component interactions and translocon assembly. Metal tagging transmission electron microscopy revealed the dimensions of TatA assemblies, which prompted molecular dynamics simulations. These showed that interacting TMHs of larger TatA assemblies can thin the membrane together with laterally aligned tilted APHs that generate a deep V-shaped groove. The conserved hydrophobic mismatch may thus be important for membrane destabilization during Tat transport, and the exact length of 12 hydrophobic residues could be a compromise between functionality and proton leakage minimization.

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IS1397 Is Active for Transposition into the Chromosome of Escherichia coli K-12 and Inserts Specifically into Palindromic Units of Bacterial Interspersed Mosaic Elements

Journal of Bacteriology ◽

10.1128/jb.181.22.6929-6936.1999 ◽

1999 ◽

Vol 181 (22) ◽

pp. 6929-6936 ◽

Cited By ~ 15

Author(s):

Jean-Marie Clément ◽

Caroline Wilde ◽

Sophie Bachellier ◽

Patricia Lambert ◽

Maurice Hofnung

Keyword(s):

Escherichia Coli ◽

Mobile Genetic Element ◽

Basic Element ◽

Genetic Element ◽

Repeated Element ◽

E Coli ◽

Intergenic Regions ◽

Natural Isolates ◽

K 12

ABSTRACT We demonstrate that IS1397, a putative mobile genetic element discovered in natural isolates of Escherichia coli, is active for transposition into the chromosome of E. coliK-12 and inserts specifically into palindromic units, also called repetitive extragenic palindromes, the basic element of bacterial interspersed mosaic elements (BIMEs), which are found in intergenic regions of enterobacteria closely related to E. coli andSalmonella. We could not detect transposition onto a plasmid carrying BIMEs. This unprecedented specificity of insertion into a well-characterized chromosomal intergenic repeated element and its evolutionary implications are discussed.

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Molecular population genetics of Escherichia coli: DNA sequence diversity at the celC, crr, and gutB loci of natural isolates.

Molecular Biology and Evolution ◽

10.1093/oxfordjournals.molbev.a040751 ◽

1992 ◽

Keyword(s):

Escherichia Coli ◽

Population Genetics ◽

Dna Sequence ◽

Sequence Diversity ◽

Molecular Population Genetics ◽

Natural Isolates

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Stationary-Phase Acid Resistance and Injury of Recent Bovine Escherichia coli O157 and non-O157 Biotype I Escherichia coli Isolates†

Journal of Food Protection ◽

10.4315/0362-028x-67.3.583 ◽

2004 ◽

Vol 67 (3) ◽

pp. 583-590 ◽

Cited By ~ 20

Author(s):

E. D. BERRY ◽

G. A. BARKOCY-GALLAGHER ◽

G. R. SIRAGUSA

Keyword(s):

Escherichia Coli ◽

Stationary Phase ◽

Acid Resistance ◽

Low Ph ◽

Acid Adaptation ◽

E Coli ◽

Log Reduction ◽

Natural Isolates ◽

Acidic Conditions ◽

Ph Challenge

Stationary-phase acid resistance and the induction of acid resistance were assessed for recent bovine carcass isolates of Escherichia coli, including 39 serotype O157 strains and 20 non-O157 strains. When grown to stationary phase in the absence of glucose and without prior acid exposure, there was a range of responses to a pH challenge of 6 h at pH 2.5. However, populations of 53 of the 59 E. coli isolates examined were reduced by less than 2.00 log CFU/ml, and populations of 24 of these isolates were reduced by less than 1.00 log CFU/ml. In contrast, there was little variation in population reductions when the E. coli were grown with glucose and preadapted to acidic conditions. With few exceptions, acid adaptation improved survival to the acid challenge, with 57 of the 59 isolates exhibiting a log reduction of less than 0.50. Differences in acid resistance or the ability to adapt to acidic conditions between E. coli O157:H7 and non-O157 commensal E. coli were not observed. However, we did find that the E. coli O157 were disposed to greater acid injury after the low pH challenge than the non-O157 E. coli, both for cells that were and were not adapted to acidic conditions before the challenge. The enhancement of low pH survival after acid adaptation that was seen among these recent natural isolates of E. coli O157 further supports the idea that the previous environment of this pathogen should be a consideration when designing microbial safety strategies for foods preserved by low pH and acid.

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Molecular Population Genetics of Escherichia coli: DNA Sequence Diversity at the celC crr, and gutB Loci of Natural Isolates

Molecular Biology and Evolution ◽

10.1093/oxfordjournals.molbev.a040790 ◽

1992 ◽

Keyword(s):

Escherichia Coli ◽

Population Genetics ◽

Dna Sequence ◽

Sequence Diversity ◽

Molecular Population Genetics ◽

Natural Isolates

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Antibiotic resistance plasmids spread among natural isolates of Escherichia coli in spite of CRISPR elements

Microbiology ◽

10.1099/mic.0.060814-0 ◽

2012 ◽

Vol 158 (12) ◽

pp. 2997-3004 ◽

Cited By ~ 39

Author(s):

Marie Touchon ◽

Sophie Charpentier ◽

Dominique Pognard ◽

Bertrand Picard ◽

Guillaume Arlet ◽

...

Keyword(s):

Escherichia Coli ◽

Antibiotic Resistance ◽

Resistance Plasmids ◽

Natural Isolates

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Absence of Internalization of Escherichia coli O157:H7 into Germinating Tissue of Field-Grown Leafy Greens

Journal of Food Protection ◽

10.4315/0362-028x.jfp-13-216 ◽

2014 ◽

Vol 77 (2) ◽

pp. 189-196 ◽

Cited By ~ 18

Author(s):

MARILYN C. ERICKSON ◽

CATHY C. WEBB ◽

JUAN CARLOS DÍAZ-PÉREZ ◽

LINDSEY E. DAVEY ◽

ALISON S. PAYTON ◽

...

Keyword(s):

Escherichia Coli ◽

Contaminated Soil ◽

Spinacia Oleracea ◽

Field Studies ◽

Growth Chamber ◽

Escherichia Coli O157 ◽

Apparent Lack ◽

E Coli ◽

Leafy Greens ◽

Natural Isolates

Both growth chamber and field studies were conducted to investigate the potential for Escherichia coli O157:H7 to be internalized into leafy green tissue when seeds were germinated in contaminated soil. Internalized E. coli O157:H7 was detected by enrichment in both spinach (Spinacia oleracea L.) and lettuce (Lactuca sativa L.) seedlings when seeds were germinated within the growth chamber in autoclaved and nonautoclaved soil, respectively, contaminated with E. coli O157:H7 at 2.0 and 3.8 log CFU/g, respectively. Internalized E. coli O157:H7 populations could be detected by enumeration within leafy green tissues either by increasing the pathogen levels in the soil or by autoclaving the soil. Attempts to maximize the exposure of seed to E. coli O157:H7 by increasing the mobility of the microbe either through soil with a higher moisture content or through directly soaking the seeds in an E. coli O157:H7 inoculum did not increase the degree of internalization. Based on responses obtained in growth chamber studies, internalization of E. coli O157:H7 surrogates (natural isolates of Shiga toxin–negative E. coli O157:H7 or recombinant [stx- and eae-negative] outbreak strains of E. coli O157:H7) occurred to a slightly lesser degree than did internalization of the virulent outbreak strains of E. coli O157:H7. The apparent lack of internalized E. coli O157:H7 when spinach and lettuce were germinated from seed in contaminated soil (ca. 3 to 5 log CFU/g) in the field and the limited occurrence of surface contamination on the seedlings suggest that competition from indigenous soil bacteria and environmental stresses were greater in the field than in the growth chamber. On the rare occasion that soil contamination with E. coli O157:H7 exceeded 5 log CFU/g in a commercial field, this pathogen probably would not be internalized into germinating leafy greens and/or would not still be present at the time of harvest.

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