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Non-congruent relationships between variation in emm gene sequences and the population genetic structure of group A
A M Whatmore1, V Kapur, D J Sullivan
1Department of Microbiology, University of Newcastle upon Tyne, Medical School, UK.
Abstract:
To examine the molecular population genetics of the M protein family of Streptococcus pyogenes (group A Streptococcus), the 5' regions of polymerase chain reaction-amplified emm products from 79 M serotypes were sequenced and the phylogeny was compared to estimates of overall genetic relationships among strains determined by multilocus enzyme electrophoresis. Although the 5' emm sequences from several strains designated as distinct M types were identical or almost identical, the overall pattern is characterized by very extensive variation. The composition of distinct emm sequence clusters generally parallels the ability of strains to express serum opacity factor and in some cases historical associations of certain M types with acute rheumatic fever, but not with M types classified as nephritogenic. For many strains there is a lack of congruency between variation in 5' emm sequences and estimates of overall chromosomal relationships, which is undoubtedly due to horizontal transfer and recombination of emm sequences. The results of these studies provide insights into the nature and extent of emm sequence variation and describe how this variation 'maps' onto the population genetic structure of extant S. pyogenes lineages. The complexity of emm sequence and streptococcal cell lineage relationships revealed by this analysis has significant implications for understanding evolutionary events generating strain diversity and the epidemiology of S. pyogenes diseases.
Insights
Molecular population genetics reveal extensive variation in Streptococcus pyogenes M protein (emm) gene sequences. This diversity, driven by horizontal gene transfer, impacts strain evolution and disease epidemiology.
Area of Science:
- Microbiology
- Population Genetics
- Molecular Evolution
Background:
- Streptococcus pyogenes (group A Streptococcus) is a significant human pathogen.
- The M protein (emm) gene family plays a crucial role in S. pyogenes virulence and serotyping.
- Understanding the genetic diversity of emm genes is essential for tracking pathogen evolution and epidemiology.
Purpose of the Study:
- To investigate the molecular population genetics of the Streptococcus pyogenes M protein (emm) gene family.
- To compare the phylogeny of emm gene sequences with overall genetic relationships among S. pyogenes strains.
- To elucidate the impact of emm sequence variation on S. pyogenes population structure and disease associations.
Main Methods:
- Sequencing of the 5' regions of polymerase chain reaction-amplified emm products from 79 M serotypes.
- Comparison of emm sequence phylogeny with genetic relationships determined by multilocus enzyme electrophoresis.
- Analysis of correlations between emm sequence clusters, serum opacity factor expression, and disease associations (rheumatic fever, nephritogenic types).
Main Results:
- Extensive variation observed in 5' emm sequences, with some distinct M types showing identical or near-identical sequences.
- emm sequence clusters generally correlate with serum opacity factor expression and historical associations with acute rheumatic fever, but not nephritogenic types.
- Significant lack of congruency between emm sequence variation and overall chromosomal relationships, indicating horizontal gene transfer and recombination of emm sequences.
Conclusions:
- Horizontal transfer and recombination are major drivers of emm sequence variation in Streptococcus pyogenes.
- The complex interplay between emm sequence variation and S. pyogenes lineage relationships influences strain diversity.
- Understanding these evolutionary dynamics is critical for comprehending the epidemiology of S. pyogenes-associated diseases.