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Evidence consistent with horizontal transfer of the gene (emm12) encoding serotype M12 protein between group A and
W J Simpson1, J M Musser, P P Cleary
1Department of Microbiology, University of Minnesota, Minneapolis 55455.
Abstract:
Human isolates of Lancefield group G streptococci harbor sequences homologous with the structural gene (emm) encoding M protein, a major virulence factor in Streptococcus pyogenes (a group A Streptococcus species). We used DNA-DNA hybridization, restriction endonuclease chromosomal profiling, and multilocus enzyme electrophoresis to examine genetic relationships between group A and group G streptococcal strains expressing homologous serologic type 12 M (M12) protein. All M12 group A strains studied had very similar restriction endonuclease genomic profiles and multilocus enzyme genotypes. In contrast, the restriction enzyme genomic profile and multilocus enzyme genotype of the M12 group G strain CS140 were strikingly different from those characterizing the M12 group A organisms. DNA-DNA hybridization studies revealed, on average, 57% genomic similarity between the M12 group A and group G strains. Taken together, our data demonstrate that a gene encoding M12 protein occurs in two highly divergent chromosomal backgrounds, a result suggesting that an episode of horizontal gene transfer and recombination has occurred between two streptococcal lineages.
Insights
Lancefield group G streptococci share M protein genes with Streptococcus pyogenes. Genetic analysis reveals distinct chromosomal backgrounds, suggesting horizontal gene transfer between streptococcal lineages.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Lancefield group G streptococci possess genes similar to the M protein gene (emm) found in Streptococcus pyogenes (group A).
- M protein is a significant virulence factor in Streptococcus pyogenes.
Purpose of the Study:
- To investigate the genetic relationships between group A and group G streptococcal strains that express homologous serologic type 12 M (M12) protein.
- To determine if the M12 gene resides in similar or divergent genetic contexts within these two streptococcal groups.
Main Methods:
- DNA-DNA hybridization was employed to assess overall genomic similarity.
- Restriction endonuclease chromosomal profiling was used to compare genomic structures.
- Multilocus enzyme electrophoresis (MLEE) was utilized to analyze genetic diversity at multiple enzyme loci.
Main Results:
- Group A streptococcal strains expressing M12 protein exhibited highly similar genomic profiles and MLEE genotypes.
- The group G streptococcal strain CS140, also expressing M12 protein, displayed markedly different genomic profiles and MLEE genotypes compared to group A strains.
- DNA-DNA hybridization indicated approximately 57% genomic similarity between the M12 group A and group G strains.
Conclusions:
- The gene encoding M12 protein exists in two highly divergent chromosomal backgrounds.
- The findings strongly suggest an occurrence of horizontal gene transfer and recombination between distinct streptococcal lineages.