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Phylogenetic analysis of Shiga toxin 1 and Shiga toxin 2 genes associated with disease outbreaks.

Lee JE, Reed J, Shields MS, Spiegel KM, Farrell LD, Sheridan PP - BMC Microbiol. (2007)

Bottom Line: The analysis confirmed the Stx1 and Stx2 divergence, and showed that there is generally more sequence variation among stx2 genes than stx1.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Idaho State University, 921 South 8th Ave,, Pocatello, ID 83209-8007, USA. james.e.lee@amedd.army.mil

ABSTRACT

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.

Conclusion: 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.

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Related in: MedlinePlus

Unrooted Maximum Likelihood Nucleotide Phylogenetic Tree of all Shiga Toxin Sequences. The horizontal bar shows 0.1 nucleotide substitutions per site.
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Figure 8: Unrooted Maximum Likelihood Nucleotide Phylogenetic Tree of all Shiga Toxin Sequences. The horizontal bar shows 0.1 nucleotide substitutions per site.

Mentions: This investigation into the phylogenetic relationships among Shiga toxins confirmed that the two major groups, Stx1 and Stx2, are easily differentiated by both their amino acid and nucleotide sequences. The phylogram in Figure 8 shows stx1 and stx2 forming two distinct clades with stx2f branching off significantly from both. The stx1 group displayed an almost flat phylogeny whereas the stx2 group has much more sequence diversity. Stx2d, Stx2e and Stx2g all show at least 91% similarity to the EDL933 stx2 gene. The Stx2f amino acid and nucleotide sequences are only 72.5 and 70.4 percent similar to EDL933 Stx2 sequences, respectively, making it the most divergent Stx2 found to date. The greater diversity of Stx2 sequences could be the result of sampling bias. Since the majority of the gene sequences came from human outbreak pathogens and because Stx2 is associated with more severe disease, this could have an effect on what strains are recovered. Despite the fact that diarrheal illness is a leading causes of death worldwide [40], most sources providing isolates used in this study are located in areas with well established public health systems. This source location could also introduce bias into the isolates investigated.


Phylogenetic analysis of Shiga toxin 1 and Shiga toxin 2 genes associated with disease outbreaks.

Lee JE, Reed J, Shields MS, Spiegel KM, Farrell LD, Sheridan PP - BMC Microbiol. (2007)

Unrooted Maximum Likelihood Nucleotide Phylogenetic Tree of all Shiga Toxin Sequences. The horizontal bar shows 0.1 nucleotide substitutions per site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211750&req=5

Figure 8: Unrooted Maximum Likelihood Nucleotide Phylogenetic Tree of all Shiga Toxin Sequences. The horizontal bar shows 0.1 nucleotide substitutions per site.
Mentions: This investigation into the phylogenetic relationships among Shiga toxins confirmed that the two major groups, Stx1 and Stx2, are easily differentiated by both their amino acid and nucleotide sequences. The phylogram in Figure 8 shows stx1 and stx2 forming two distinct clades with stx2f branching off significantly from both. The stx1 group displayed an almost flat phylogeny whereas the stx2 group has much more sequence diversity. Stx2d, Stx2e and Stx2g all show at least 91% similarity to the EDL933 stx2 gene. The Stx2f amino acid and nucleotide sequences are only 72.5 and 70.4 percent similar to EDL933 Stx2 sequences, respectively, making it the most divergent Stx2 found to date. The greater diversity of Stx2 sequences could be the result of sampling bias. Since the majority of the gene sequences came from human outbreak pathogens and because Stx2 is associated with more severe disease, this could have an effect on what strains are recovered. Despite the fact that diarrheal illness is a leading causes of death worldwide [40], most sources providing isolates used in this study are located in areas with well established public health systems. This source location could also introduce bias into the isolates investigated.

Bottom Line: The analysis confirmed the Stx1 and Stx2 divergence, and showed that there is generally more sequence variation among stx2 genes than stx1.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Idaho State University, 921 South 8th Ave,, Pocatello, ID 83209-8007, USA. james.e.lee@amedd.army.mil

ABSTRACT

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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus