DEVELOPMENT OF COMPETENCE IN STREPTOCOCCUS-PNEUMONIAE - PHEROMONE AUTOINDUCTION AND CONTROL OF QUORUM SENSING BY THE OLIGOPEPTIDE PERMEASE

Competence for genetic transformation in the human pathogen Streptococ cus pneumoniae is a transient physiological property. A competence-sti mulating peptide, CSP, was recently identified as the processed produc t of the comC gene, As conflicting results have been reported regardin g CSP autoinduction, we monitored the CSP-induced expression of comCDE in derivatives of strain R6 using comC::lacZ fusions, Autoinduction w as demonstrated in this genetic background. The kinetics of CSP-induce d transcription of comCDE and of a late competence-induced (cin) opero n were compared, While the comCDE mRNA revel was highest 5 min after C SP addition then decreased, maximal cin expression required 10 min exp osure to CSP. Transformation frequencies paralleled cin expression. Af ter 20 min exposure to CSP, both mRNAs disappeared almost completely, providing evidence for an intrinsic mechanism for shutting off CSP sig nal transduction, Investigation of spontaneous competence development in mixed cultures indicated that transformation of wild-type cells was delayed in the presence of CSP non-producers, consistent with a direc t role of CSP in quorum sensing, The effect of varying inoculum size o n the timing of competence development was investigated. While compete nce developed in wild-type cultures at a similar critical density, abo ut OD550 = 0.15, a mutant lacking the three oligopeptide-binding lipop roteins transformed at a 50-fold reduced cell density, The latter effe ct was mimicked in a strain harbouring a duplication of comC. Altogeth er, these results suggest that CSP does not accumulate passively in pn eumoccal cultures, but that comCDE basal expression can be modulated.