Transcriptome analysis reveals that CIpXP proteolysis controls key virulence properties of Streptococcus mutans

The CIpXP proteolytic complex is critical for maintaining cellular homeostasis, as well as expression of virulence properties. However, with the exception of the Spx global regulator, the molecular mechanisms by which the CIpXP complex exerts its influence in Streptococcus mutans are not well understood. Here, microarray analysis was used to provide novel insights into the scope of CIpXP proteolysis in S. mutans. In a Delta cIpP strain, 288 genes showed significant changes in relative transcript amounts (P <= 0.001, twofold cut-off) as compared with the parent. Similarly, 242 genes were differentially expressed by a Delta cipX strain, 113 (47%) of which also appeared in the Delta cIpP microarrays. Several genes associated with cell growth were downregulated in both mutants, consistent with the slow-growth phenotype of the Delta clp strains. Among the upregulated genes were those encoding enzymes required for the biosynthesis of intracellular polysaccharides (gig genes) and malolactic fermentation (mle genes). Enhanced expression of glg and mle genes in Delta cIpP and Delta cipX strains correlated with increased storage of intracellular polysaccharide and enhanced malolactic fermentation activity, respectively. Expression of several genes known or predicted to be involved in competence and mutacin production was downregulated in the Delta clp strains. Follow-up transformation efficiency and deferred antagonism assays validated the microarray data by showing that competence and mutacin production were dramatically impaired in the Delta clp strains. Collectively, our results reveal the broad scope of CIpXP regulation in S. mutans homeostasis and identify several virulence-related traits that are influenced by CIpXP proteolysis.