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Global regulation by (p)ppGpp and CodY in Streptococcus mutans.

José A Lemos¹, Marcelle M Nascimento, Vanessa K Lin

¹Department of Microbiology and Immunology and Center for Oral Biology, University of Rochester Medical Center, Rochester, New York 14642, USA. jose_lemos@urmc.rochester.edu

Journal of Bacteriology

|June 10, 2008

Summary

Growth defects in Streptococcus mutans lacking alarmone synthetases are linked to the CodY regulator, not GTP levels. Basal (p)ppGpp production by RelP and RelQ is essential for growth without specific amino acids.

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Area of Science:

Microbiology
Molecular Biology
Bacterial Physiology

Background:

RelA, RelP, and RelQ enzymes produce the alarmone (p)ppGpp in Streptococcus mutans.
A strain lacking these synthetases (DeltarelAPQ) exhibits growth defects in minimal media lacking branched-chain amino acids (BCAA).

Purpose of the Study:

To investigate the correlation between growth in the absence of leucine/valine, (p)ppGpp levels, and CodY activation.
To elucidate the role of CodY in regulating BCAA biosynthesis and virulence in S. mutans.

Main Methods:

Construction and analysis of single, double, and triple mutants for (p)ppGpp synthetase enzymes.
Phenotypic studies including growth assays, biofilm formation, and low pH sensitivity.
Microarray analysis to determine the CodY regulon.
GTP level manipulation using decoyinine.

Main Results:

Basal (p)ppGpp production by RelP and RelQ is required for growth without leucine or valine.
A mutation in CodY fully restored growth in DeltarelAPQ mutants lacking leucine or valine.
S. mutans CodY is not activated by GTP, as decoyinine did not affect CodY repression or BCAA gene expression.
CodY plays a role in biofilm formation and low pH tolerance, key virulence factors.
CodY acts as both a repressor and potentially an activator of gene transcription.

Conclusions:

The growth defect of DeltarelAPQ mutants is directly mediated by CodY repression.
CodY is a critical regulator of BCAA biosynthesis, biofilm formation, and acid tolerance in S. mutans.
CodY's regulatory mechanism is independent of GTP levels in S. mutans.