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amrA encodes a putative membrane protein necessary for maximal exponential phase expression of the Mga virulence

Deborah A Ribardo1, Kevin S McIver

  • 1Department of Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-9048, USA.

Molecular Microbiology
|November 18, 2003
PubMed

Insights

A newly identified gene, amrA, is crucial for activating group A Streptococcus (GAS) virulence genes regulated by Mga. Its inactivation reduces Mga regulon activation, impacting GAS colonization and immune evasion.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • The transcriptional regulator Mga controls a network of virulence genes in group A Streptococcus (GAS).
  • These Mga-regulated genes are essential for GAS colonization and evading the host immune system.
  • Understanding factors that regulate Mga activity is key to controlling GAS infections.

Purpose of the Study:

  • To identify novel factors involved in the regulation of the Mga virulence regulon in GAS.
  • To characterize the function of a newly identified open reading frame (ORF), amrA, in Mga regulon activation.
  • To investigate the role of amrA in GAS virulence gene expression.

Main Methods:

  • Transposon mutagenesis was performed on a serotype M6 GAS reporter strain (KSM148).
  • Deletion mutants of amrA and Spy0798 were created and analyzed.
  • Northern and Western blot analyses were used to assess mga and emm gene expression and Mga protein levels.
  • Complementation studies were conducted using a nisin-inducible expression system.
  • Inactivation of amrA in a different serotype (M3) was performed to assess serotype specificity.

Main Results:

  • A novel ORF, amrA, was identified as essential for maximal Mga regulon activation during exponential growth.
  • Deletion of amrA led to reduced expression of mga and Mga-regulated virulence genes (emm).
  • The observed phenotype was specific to amrA, as deletion of the downstream ORF Spy0798 had no effect.
  • Complementation restored Mga regulon activation in amrA mutants.
  • amrA is conserved across streptococcal M types and its inactivation reduced virulence gene expression in both M6 and M3 serotypes, indicating a non-serotype-specific role.

Conclusions:

  • The gene amrA plays a critical, non-serotype-specific role in activating the Mga virulence regulon in GAS.
  • Reduced amrA expression leads to decreased transcription of Mga-regulated virulence genes.
  • The putative membrane localization and homology to cell wall synthesis transporters suggest AmrA may link bacterial growth to virulence gene expression.

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