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Mol Microbiol. 2008 Oct;70(1):112-26. doi: 10.1111/j.1365-2958.2008.06390.x. Epub 2008 Aug 4.

The cia operon of Streptococcus mutans encodes a unique component required for calcium-mediated autoregulation.

Author information

1
UCLA School of Dentistry, Los Angeles, CA 90095, USA.

Abstract

Streptococcus mutans is a primary pathogen for dental caries in humans. CiaR and CiaH of S. mutans comprise a two-component signal transduction system (TCS) involved in regulating various virulent factors. However, the signal that triggers the CiaRH response remains unknown. In this study, we show that calcium is a signal for regulation of the ciaRH operon, and that a double-glycine-containing small peptide encoded within the ciaRH operon (renamed ciaX) mediates this regulation. CiaX contains a serine + aspartate (SD) domain that is shared by calcium-binding proteins. A markerless in-frame deletion of ciaX reduced ciaRH operon expression and diminished the calcium repression of operon transcription. Point mutations of the SD domain resulted in the same phenotype as the in-frame deletion, indicating that the SD domain is required for CiaX function. Further characterization of ciaX demonstrated that it is involved in calcium-mediated biofilm formation. Furthermore, inactivation of ciaR or ciaH led to the same phenotype as the in-frame deletion of ciaX, suggesting that all three genes are involved in the same regulatory pathway. Sequence analysis and real-time RT-PCR identified a putative CiaR binding site upstream of ciaX. We conclude that the ciaXRH operon is a three-component, self-regulatory system modulating cellular functions in response to calcium.

PMID:
18681938
PMCID:
PMC2955730
DOI:
10.1111/j.1365-2958.2008.06390.x
[Indexed for MEDLINE]
Free PMC Article

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