Microarray analysis and draft genomes of two Escherichia coli O157:H7 lineage II cattle isolates FRIK966 and FRIK2000 investigating lack of Shiga toxin expression.
The existence of two separate genetic lineages of Escherichia coli O157:H7 has previously been reported, and research indicates that lineage I could be more pathogenic toward human hosts than lineage II. We have previously shown that lineage I as a group expresses higher levels of Shiga toxin 2 (Stx2) than lineage II. To help evaluate why lineage II strains do not express appreciable levels of this toxin, whole-genome microarrays were performed using Agilent custom microarrays. Gene expression of the two representative bovine lineage II strains (FRIK966 and FRIK2000) were compared with gene expression of E. coli O157:H7 EDL933 (lineage I clinical type strain). Missing or differentially expressed genes and pathways were identified. Quantitative reverse transcription-polymerase chain reaction was performed to validate the microarray data. Draft genomes of FRIK966 and FRIK2000 were sequenced using Roche Applied Science/454 GS-FLX technology shotgun and paired-end approaches followed by de novo assembly. These assemblies were compared with the lineage I genome sequences from E. coli O157:H7 EDL933. The bacteriophage 933W, which encodes the Stx2 genes, showed a notable repression in gene expression. Polymerase chain reaction primers, based upon EDL933 genomic information, were also designed against all of the potentially missing genes of this bacteriophage. Most of the structural genes associated with the bacteriophage were found to be absent from the genome of the two bovine strains. These analyses, combined with evaluation of the genomic information, suggest that transposon (IS629) rearrangements may be associated with disruption of the bacteriophage genome in the FRIK strains. The results support the hypothesis that lineage II strains may be less of a risk as human foodborne pathogens. The microarray and genome data have been made available to the scientific community to allow continuing analysis of these cattle-isolated lineage II genomes and their gene expression.
Dowd
Scot E
SE
Research and Testing Laboratory, Lubbock, Texas 79407, USA. sdowd@pathogenresearch.org
Crippen
Tawni L
TL
Sun
Yan
Y
Gontcharova
Viktoria
V
Youn
Eun
E
Muthaiyan
Arunachalam
A
Wolcott
Randall D
RD
Callaway
Todd R
TR
Ricke
Steven C
SC
D000818:Animals; D002417:Cattle / Q000382:microbiology*; D002874:Chromosome Mapping; D019295:Computational Biology / Q000379:methods; D004251:DNA Transposable Elements; D030561:Databases, Nucleic Acid; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity* / Q000821:virology; D005517:Foodborne Diseases / Q000235:genetics / Q000382:microbiology / Q000517:prevention & control; D015964:Gene Expression Regulation, Bacterial; D015321:Gene Rearrangement; D016680:Genome, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D017902:Podoviridae / Q000235:genetics; D039002:Prophages / Q000737:chemistry; D017422:Sequence Analysis, DNA; D022641:Shiga Toxin 2 / Q000235:genetics / Q000378:metabolism; D022603:Shiga Toxins / Q000235:genetics / Q000378:metabolism*; D014774:Virulence / Q000235:genetics
D004251:DNA Transposable Elements; D022641:Shiga Toxin 2; D022603:Shiga Toxins