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Insertional inactivation of streptolysin S expression is associated with altered riboflavin metabolism in
1Department of Human Microbiology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Abstract:
Transposon Tn916 mutagenesis was used to create a mutant of Streptococcus pyogenes M type 3, designated ISS417, in which the ability to produce streptolysin S (SLS) and several other exoproteins was impaired. Concomitantly, the mutant became dependent upon riboflavin for growth and was able to grow in Todd Hewitt broth (THB) when supplemented with riboflavin or riboflavinrich yeast extract. The parent strain was apparently able to utilize THB-derived components as a substitute for riboflavin, while the mutant was not. Although the parent strain grew well in synthetic medium, it was unable to produce SLS, except when it was supplemented with a small amount of THB. Thus, a component of THB was able to "trigger" SLS formation in the parent strain. The mutant grew well in this medium, but was unable to produce SLS even when it was supplemented with THB. Southern hybridization analysis revealed that the ISS417 mutant harbours a single transposon insertion in its chromosome. Phage transduction experiments showed that the riboflavin dependency and the inability to make SLS phenotypes are co-transducible. The pleotrophic properties of the ISS417 mutant differ from those reported for insertional inactivation of the mga locus which regulates production of a number of surface proteins in S. pyogenes and the sar locus which regulates production of a number of exoproteins in Staphylococcus aureus. In view of the possibility that there exist a genetic linkage between the riboflavin biosynthetic pathway and expression of the oxygen-stable SLS, we hypothesize that SLS has a role in the growth economy of S. pyogenes.
Insights
Transposon mutagenesis of Streptococcus pyogenes created a mutant dependent on riboflavin for growth, with impaired streptolysin S (SLS) production. This suggests a link between riboflavin metabolism and SLS expression, potentially impacting bacterial growth economy.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pyogenes is a significant human pathogen.
- Streptolysin S (SLS) is a key virulence factor produced by S. pyogenes.
- Regulation of exoprotein production in S. pyogenes is complex and not fully understood.
Purpose of the Study:
- To investigate the genetic basis for riboflavin dependency and impaired streptolysin S (SLS) production in Streptococcus pyogenes.
- To identify potential regulatory links between metabolic pathways and virulence factor expression.
- To characterize a novel mutant with pleiotropic defects in exoprotein production.
Main Methods:
- Transposon Tn916 mutagenesis was employed to generate mutants of S. pyogenes M type 3.
- Growth characteristics and exoprotein production (specifically SLS) were assessed under various conditions.
- Southern hybridization and phage transduction were used to analyze the genetic basis of the observed phenotypes.
Main Results:
- A mutant, ISS417, was generated exhibiting riboflavin auxotrophy and reduced SLS production.
- The riboflavin dependency and SLS deficiency phenotypes were found to be co-transducible, indicating a single genetic locus.
- The ISS417 mutant's phenotype differs from mutations in known regulatory loci like mga and sar.
- A component in Todd Hewitt broth (THB) was identified as a trigger for SLS production in the parent strain, but not the mutant.
Conclusions:
- A genetic linkage may exist between the riboflavin biosynthetic pathway and the expression of SLS in S. pyogenes.
- The study hypothesizes a role for SLS in the growth economy of S. pyogenes.
- The identified mutant provides a new tool for studying the regulation of virulence factors and metabolic dependencies in S. pyogenes.