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Published on: September 11, 2020
Comparative pathogenomic characterization of a non-invasive serotype M71 strain Streptococcus pyogenes NS53 reveals
Yun-Juan Bao1, Yang Li1,2, Zhong Liang1,3
1W.M. Keck Center for Transgene Research, University of Notre Dame, Notre Dame, IN 46556, USA.
Abstract:
The strains serotyped as M71 from group A Streptococcus are common causes of pharyngeal and skin diseases worldwide. Here we characterize the genome of a unique non-invasive M71 human isolate, NS53. The genome does not contain structural rearrangements or large-scale gene gains/losses, but encodes a full set of non-truncated known virulence factors, thus providing an ideal reference for comparative studies. However, the NS53 genome showed incongruent phenotypic implications from distinct genotypic markers. NS53 is characterized as an emm pattern D and FCT (fibronectin-collagen-T antigen) type-3 strain, typical of skin tropic strains, but is phylogenetically close to emm pattern E strains with preference for both skin and pharyngeal infections. We propose that this incongruence could result from recombination within the emm gene locus, or, alternatively, selection has been against those genetic alterations. Combined with the inability to select for CovS switching, a process is indicated whereby NS53 has been pre-adapted to specific host niches selecting against variations in CovS and many other genes. This may allow the strain to attain successful colonization and long-term survival. A balance between genetic variations and fitness may exist for this bacterium to form a stabilized genome optimized for survival in specific host environments.
Insights
This study details the genome of a unique Group A Streptococcus M71 strain, NS53, revealing genetic markers suggesting adaptation to specific host environments. The findings offer insights into bacterial adaptation and genome stabilization for long-term survival.
Area of Science:
- Microbiology
- Genomics
- Bacterial Pathogenesis
Background:
- Group A Streptococcus (GAS) M71 strains are prevalent global pathogens causing pharyngeal and skin infections.
- Understanding GAS genome variation is crucial for deciphering host-pathogen interactions and disease tropism.
Purpose of the Study:
- To characterize the genome of a unique, non-invasive M71 human isolate, NS53.
- To investigate the genetic basis for incongruent genotypic and phenotypic traits in NS53.
- To explore potential mechanisms of host niche adaptation in GAS.
Main Methods:
- Whole-genome sequencing of the NS53 strain.
- Bioinformatic analysis of genomic features, including virulence factors and emm gene locus.
- Phylogenetic analysis to determine evolutionary relationships.
- Phenotypic marker analysis (emm pattern, FCT type).
Main Results:
- The NS53 genome is stable, lacking major structural rearrangements but possessing complete virulence factors.
- NS53 exhibits conflicting genotypic markers: emm pattern D/FCT type-3 (skin-associated) yet phylogenetically close to emm pattern E (skin/pharyngeal).
- Inability to select for CovS switching suggests pre-adaptation to specific host niches, favoring genome stabilization.
Conclusions:
- The NS53 genome's unique characteristics suggest a stabilized state optimized for specific host environments.
- Recombination within the emm gene locus or selection against genetic alterations may explain observed incongruences.
- A balance between genetic variation and host fitness likely drives GAS genome evolution and adaptation for colonization and survival.
