The sagA/pel locus does not regulate the expression of the M protein of the M1T1 lineage of group A Streptococcus

Abstract

Altered expression of Group A Streptococcus (GAS) virulence factors, including the M protein, can result as a consequence of spontaneous genetic changes that occur during laboratory and animal passage. Occurrence of such secondary mutations during targeted gene deletion could confound the interpretation of effects attributable to the function of the gene being investigated. Contradicting reports on whether the sagA/pel locus regulates the M protein-encoding emm might be due to inconsistent occurrence of mutations unrelated with sagA. This study examined the possibility that altered emm expression observed in association with sagA/pel deletion mutants is artifactual. sagA deletion mutants (MGAS2221ΔsagA) of M1T1 isolate MGAS2221 obtained using liquid broth for GAS growth during the deletion process had diminished emm transcription and no detectable M protein production. In contrast, a ΔsagA mutant of another closely genetically related M1T1 isolate had normal emm expression. The sagB gene does not regulate emm; however, one of three MGAS2221ΔsagB mutants had diminished emm expression. The emm regulator mga was downregulated in these M protein expression-negative strains. These results argue that sagA deletion does not directly cause the downregulation of emm expression. Indeed, two MGAS2221ΔsagA mutants obtained using agar plates for GAS growth during the deletion process both had normal emm expression. We conclude that the sagA/pel locus does not regulate emm expression in the M1T1 lineage and provide a protocol for targeted gene deletion that we find less prone to the generation of mutants exhibiting downregulation in emm expression.

Keywords: :

• group A Streptococcus
• streptolysin S
• pel
• sagA
• M protein
• emm
• gene expression and regulation
• phase variation
• gene deletion
• virulence factor

This article is referred to by:

The prince and the pauper

10.4161/viru.26413

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

This work was supported in part by grants AI095704, AI097703, and GM103500-09 from the National Institutes of Health, USDA Animal Formula Fund, and the Montana State Agricultural Experimental Station. We thank Dr James Dale at University of Tennessee Health Science Center for providing anti-M protein antisera and Dr Daniel Nelson at University of Maryland for providing PlyC.