Molecular analysis of mutS expression and mutation in natural isolates of pathogenic Escherichia coli.
Deficiencies in the MutS protein disrupt methyl-directed mismatch repair (MMR), generating a mutator phenotype typified by high mutation rates and promiscuous recombination. How such deficiencies might arise in the natural environment was determined by analysing pathogenic strains of Escherichia coli. Quantitative Western immunoblotting showed that the amount of MutS in a wild-type strain of the enterohaemorrhagic pathogen E. coli O157 : H7 decreased about 26-fold in stationary-phase cells as compared with the amount present during exponential-phase growth. The depletion of MutS in O157 : H7 is significantly greater than that observed for a laboratory-attenuated E. coli K-12 strain. In the case of stable mutators, mutS defects in strains identified among natural isolates were analysed, including two E. coli O157 : H7 strains, a diarrhoeagenic E. coli O55 : H7 strain, and a uropathogenic strain from the E. coli reference (ECOR) collection. No MutS could be detected in the four strains by Western immunoblot analyses. RNase T2 protection assays showed that the strains were either deficient in mutS transcripts or produced transcripts truncated at the 3' end. Nucleotide sequence analysis revealed extensive deletions in the mutS region of three strains, ranging from 7.5 to 17.3 kb relative to E. coli K-12 sequence, while the ECOR mutator contained a premature stop codon in addition to other nucleotide changes in the mutS coding sequence. These results provide insights into the status of the mutS gene and its product in pathogenic strains of E. coli.
Li
Baoguang
B
Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
Tsui
Ho-Ching T
HT
Department of Microbiology and Molecular Genetics, University of Texas Houston Medical School, Houston, TX 77030, USA.
LeClerc
J Eugene
JE
Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
Dey
Manashi
M
Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
Winkler
Malcolm E
ME
Department of Microbiology and Molecular Genetics, University of Texas Houston Medical School, Houston, TX 77030, USA.
Cebula
Thomas A
TA
Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins; D020137:Base Pair Mismatch; D004260:DNA Repair; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D051719:MutS DNA Mismatch-Binding Protein; D009154:Mutation; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D000251:Adenosine Triphosphatases; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli