Streptococcus mutans, the primary etiological agent of human dental caries, has adapted numerous strategies to combat environmental insults that allow for the organism to outcompete other commensal oral streptococci and increase in proportion within the niche of supragingival plaque, leading eventually to pathogenic biofilms and caries development. Of particular interest, S. mutans displays complex regulation of natural genetic competence or the acquisition of exogenous DNA, with competence development closely intertwined to other general stress tolerance responses. The studies provided here show further evidence of the integration of stress tolerance in genetic competence by identifying new insights into the role of the RcrRPQ operon, the molecular alarmone (p)ppGpp and uncover a novel regulator of genetic competence, XrpA.
During RNA-Seq analysis of the ΔrcrR-NP strain, we observed rcrR-NP expresses a comX transcript lacking the 5’ region possibly due to mRNA processing. We also identified an open reading frame within this shorter transcript encoding a 69 aa peptide we have termed XrpA (ComX regulatory peptide A) that is in the +1 reading frame with respect to comX. Mutational analysis and translational fusions of xrpA show it to be a produced peptide within S. mutans. We further observe that XrpA is an antagonist of comX most likely through interaction and inhibition of ComRS, the proximal regulators of comX expression. Investigation into xrpA translation reveals a complex regulatory mechanism that is dependent on comX translation and most likely involves a ribosomal pausing or slippage event.
We also identify a clear linkage between (p)ppGpp levels and competence development through the dual (p)ppGpp synthetase/hydrolase enzyme RelA. Deletion of relA results in decreased growth inhibition by the comX inducing peptide XIP and decreased transformation efficiency due to a decrease in comR promoter activity. Finally a relA-deficient rcrR-NP strain shows a reversion in the non-transformable phenotype, suggesting a closer relationship of RelA with the RcrRPQ operon than was previously appreciated. In toto, the results presented here uncover novel pathways and regulators of genetic competence development in S. mutans by the general stress tolerance response that open multiple new areas of investigation and could provide attractive targets for anti-caries therapeutics.
|Advisor:||Burne, Robert A.|
|School:||University of Florida|
|Department:||Immunology and Microbiology|
|School Location:||United States -- Florida|
|Source:||DAI-B 79/04(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Microbiology, Dentistry|
|Keywords:||(p)ppgpp, bacterial signaling, biofilms|
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