G. Alloing et al., COMPETENCE PHEROMONE, OLIGOPEPTIDE PERMEASE, AND INDUCTION OF COMPETENCE IN STREPTOCOCCUS-PNEUMONIAE, Molecular microbiology, 21(3), 1996, pp. 471-478
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.