PRJNA436941
High-resolution profiles of the CSP signaling pathway in Streptococcus mitis reveal core and strain-specific regulated genes
In streptococci of the mitis group, competence for natural transformation is a transient physiological state triggered by competence stimulating peptides (CSPs). Although low transformation yields and the absence of a widespread functional competence system have been reported for Streptococcus mitis, recent studies revealed that, at least for some strains, high efficiencies can be achieved following optimization protocols. By using RNA-seq, the global CSP response of two S. mitis, the type strain NCTC12261T and SK321, was mapped at single base resolution. All known genes induced by ComE in Streptococcus pneumoniae, including sigX, were upregulated in the two strains. Likewise, all sets of streptococcal SigX core genes involved in extracellular DNA uptake, recombination, and fratricide were upregulated. No significant differences in the set of induced genes were observed when the type strain was grown in rich or semi-defined media. Five operons unique to S. mitis with a SigX-box in the promoter region were identified, two specific to SK321, and one specific to NCTC12261T. Two of the strain-specific operons coded for different bacteriocins. Deletion of the unique S. mitis competence genes had no effect on transformation. Overall, comparison of the global transcriptome in response to CSP shows the conservation of the ComE and SigX-core regulons in competent S. mitis isolates, as well as species and strain-specific genes. Although a range of S. mitis exhibit truncations in key competence genes, this study shows that in transformable strains, competence seems to depend on the same core genes previously identified in S. pneumoniae.