Phylogenetic analysis of Shiga toxin 1 and Shiga toxin 2 genes associated with disease outbreaks.
BACKGROUND
Shiga toxins 1 and 2 (Stx1 and Stx2) are bacteriophage-encoded proteins that have been associated with hemorrhagic colitis, hemolytic uremic syndrome and other severe disease conditions. Stx1 and Stx2 are genetically and immunologically distinct but share the same compound toxin structure, method of entry and enzymatic function.


RESULTS
Phylogenetic analysis was performed using Stx1 and Stx2 amino acid and nucleotide sequences from 41 strains of Escherichia coli, along with known stx sequences available from GenBank. The analysis confirmed the Stx1 and Stx2 divergence, and showed that there is generally more sequence variation among stx2 genes than stx1. The phylograms showed generally flat topologies among our strains' stx1 and stx2 genes. In the stx2 gene, 39.5% of the amino acid sites display very low nonsynonymous to synonymous substitution ratios.


CONCLUSIONS
The stx1 and stx2 genes used in this phylogenetic study show sequence conservation with no significant divergence with respect to place or time. These data could indicate that Shiga toxins are experiencing purifying selection.
Department of Biological Sciences, Idaho State University, 921 South 8th Ave,, Pocatello, ID 83209-8007, USA. james.e.lee@amedd.army.mil
James E
JE
Lee
Junelina
J
Reed
Malcolm S
MS
Shields
Kathleen M
KM
Spiegel
Larry D
LD
Farrell
Peter P
PP
Sheridan
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D004269:DNA, Bacterial; D004196:Disease Outbreaks; D004926:Escherichia coli / Q000145:classification / Q000235:genetics*; D019143:Evolution, Molecular; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D022622:Shiga Toxin 1 / Q000737:chemistry / Q000235:genetics*; D022641:Shiga Toxin 2 / Q000737:chemistry / Q000235:genetics*
D004269:DNA, Bacterial; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2