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Streptococcus pyogenes polymyxin B-resistant mutants display enhanced ExPortal integrity.

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Streptococcus pyogenes ExPortal integrity is key for toxin secretion. Polymyxin B resistance in mutants reveals a membrane stress response that enhances ExPortal organization and protects against antimicrobial peptides.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Cell Biology

Background:

  • The ExPortal is a specialized membrane microdomain in Streptococcus pyogenes responsible for protein secretion.
  • This organelle is crucial for the secretion of various toxins and is sensitive to disruption by cationic antimicrobial peptides like Polymyxin B.

Purpose of the Study:

  • To identify genetic factors influencing ExPortal organization and integrity.
  • To understand the mechanisms underlying resistance to Polymyxin B and enhanced ExPortal stability.

Main Methods:

  • A genetic screen was employed to isolate spontaneous Polymyxin B-resistant mutants.
  • Whole-genome resequencing was performed on resistant mutants to identify genetic alterations.
  • Mutant construction via gene deletion or insertion was used to validate identified genes.

Main Results:

  • Mutations in 10 core gene groups were identified in resistant mutants, primarily affecting ExPortal integrity.
  • Seven genes conferred resistance and enhanced ExPortal integrity through loss-of-function mutations.
  • Three genes likely involved gain-of-function or combinatorial effects, including regulators of lipid biosynthesis, nutrient acquisition, and stress responses.
  • A specific mutation in pstS suggests a molecular switch mechanism for stress adaptation.

Conclusions:

  • A novel membrane stress response pathway in Streptococcus pyogenes enhances ExPortal integrity.
  • This stress response confers resistance to cationic antimicrobial peptides.
  • Identified genes provide new insights into ExPortal organization and regulation of secreted virulence factors like SpeB.