Discovery of novel peptides regulating competence development in Streptococcus mutans

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The RcrR transcriptional repressor and RcrPQ efflux pumps regulate stress tolerance and genetic competence in Streptococcus mutans.
• Mutations in rcrR lead to distinct competence phenotypes: hyper-transformable (polar mutation) and non-transformable (nonpolar mutation).

Purpose of the Study:

• To investigate the mechanisms by which rcrR mutations impact genetic competence in Streptococcus mutans.
• To identify novel regulatory roles of components within the rcrRPQ operon.

Main Methods:

• Analysis of polar (ΔrcrR-P) and nonpolar (ΔrcrR-NP) rcrR mutants.
• Deletion and start codon mutations of identified open reading frames (ORFs) encoding peptides.
• Overexpression studies of peptides and ABC transporters.
• Detection of FLAG-tagged peptides.
• Correlation of competence phenotypes with ComX protein levels.

Main Results:

• Two novel peptides (27 and 42 amino acids) encoded at the 3' end of rcrQ are upregulated in the ΔrcrR-NP strain.
• Deletion or mutation of these peptide ORFs in the ΔrcrR-NP background restored competence and competence-stimulating peptide (CSP) sensitivity.
• Overexpression of these peptides or peptide-lacking ABC exporters impaired competence development.
• Peptide function was affected by FLAG tagging, and peptide levels correlated with ComX protein levels.

Conclusions:

• The rcrRPQ operon encodes novel peptides that play a critical role in regulating genetic competence development in Streptococcus mutans.
• These peptides, in conjunction with the RcrPQ efflux pumps, represent new regulatory mechanisms for competence and stress tolerance.
• The rcrRPQ-encoded peptides are potential therapeutic targets for diminishing Streptococcus mutans virulence.