COMPETENCE PHEROMONE, OLIGOPEPTIDE PERMEASE, AND INDUCTION OF COMPETENCE IN STREPTOCOCCUS-PNEUMONIAE

An unmodified heptadecapeptide pheromone capable of eliciting competen ce for genetic transformation in Streptococcus pneumoniae has recently been identified and characterized, In considering possible signal-tra nsduction mechanisms for the peptide, the previously characterized Ami oligopeptide permease and the three highly homologous oligopeptide-bi nding lipoproteins, AmiA, AliA, and AliB, appeared to he good candidat es for receptors. We therefore compared the spontaneous transformabili ty of Ami, AliA and AliB mutants to that of an isogenic wild-type stra in and we investigated the response of the various mutants to treatmen t with synthetic competence-stimulating peptide (CSP). Our results cle arly demonstrate that neither Ami nor any of the three highly homologo us oligopeptide-binding lipoproteins identified so far in S. pneumonia e are required for competence induction following treatment with synth etic CSP, Although the existence of a fourth unidentified oligopeptide -binding lipoprotein and/or a second oligopeptide permease operon coul d not be completely ruled out, we favour the hypothesis that CSP signa l transmission rather involves a two-component regulatory system, Alth ough none of the single or double Ami and Ali mutants tested appeared severely affected for competence, an exceptional aliB plasmid-insertio n mutation abolished competence completely. In addition, the triple Am iA-AliA-AliB mutant differed from wild type in showing no sharp peak o f competence but exhibiting transformability throughout the exponentia l phase of growth. These and previous observations are discussed and a general hypothesis is proposed to account for the modulation of compe tence by peptide permease mutants in S. pneumoniae.