Streptococcus sanguinis Non-coding csRNAs Negatively Regulate Expression of Type IV Pilus Retraction ATPase PilT and Biofilm Formation

Small non-coding RNAs (sRNAs) have been identified as important regulators of gene expression in various cellular processes. Cia-dependent small RNAs (csRNAs), a group of sRNAs that are controlled by the two-component regulatory system CiaRH, are widely conserved in streptococci, but their targets have been identified only in , a pioneer colonizer of teeth and one of the most predominant bacteria in the early oral biofilm, has been shown to have six csRNAs. Using computational target prediction and the luciferase reporter assay, we identified , a constituent of the type IV pili operon, as a negative regulatory target for one of the csRNAs, namely csRNA1-1, in RNA-RNA electrophoretic mobility shift assay using a nucleotide exchange mutant of csRNA1-1 revealed that csRNA1-1 binds directly to mRNA. In addition, csRNA1-1 and csRNA1-2, a putative gene duplication product of csRNA1-1 that is tandemly located in the genome, negatively regulated biofilm formation. These results suggest the involvement of csRNAs in the colonization step of .