Alloing G, Martin B, Granadel C, Claverys J P
Laboratoire de Microbiologie et Génétique Moléculaire CNRS-UPR 9007, Université Paul Sabatier, Toulouse, France.
Mol Microbiol. 1998 Jul;29(1):75-83. doi: 10.1046/j.1365-2958.1998.00904.x.
Competence for genetic transformation in the human pathogen Streptococcus pneumoniae is a transient physiological property. A competence-stimulating peptide, CSP, was recently identified as the processed product of the comC gene. As conflicting results have been reported regarding CSP autoinduction, we monitored the CSP-induced expression of comCDE in derivatives of strain R6 using comC::lacZ fusions. Autoinduction was demonstrated in this genetic background. The kinetics of CSP-induced transcription of comCDE and of a late competence-induced (cin) operon were compared. While the comCDE mRNA level was highest 5 min after CSP addition then decreased, maximal cin expression required 10 min exposure to CSP. Transformation frequencies paralleled cin expression. After 20 min exposure to CSP, both mRNAs disappeared almost completely, providing evidence for an intrinsic mechanism for shutting off CSP signal 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 direct role of CSP in quorum sensing. The effect of varying inoculum size on the timing of competence development was investigated. While competence developed in wild-type cultures at a similar critical density, about OD550 = 0.15, a mutant lacking the three oligopeptide-binding lipoproteins transformed at a 50-fold reduced cell density. The latter effect was mimicked in a strain harbouring a duplication of comC. Altogether, these results suggest that CSP does not accumulate passively in pneumoccal cultures, but that comCDE basal expression can be modulated.
人类病原体肺炎链球菌中的遗传转化能力是一种短暂的生理特性。一种 competence-stimulating peptide（CSP）最近被鉴定为 comC 基因的加工产物。由于关于 CSP 自诱导的报道结果相互矛盾，我们使用 comC::lacZ 融合体监测了 R6 菌株衍生物中 CSP 诱导的 comCDE 表达。在这种遗传背景下证实了自诱导现象。比较了 CSP 诱导的 comCDE 和晚期感受态诱导（cin）操纵子转录的动力学。虽然 comCDE mRNA 水平在添加 CSP 后 5 分钟时最高，然后下降，但 cin 的最大表达需要暴露于 CSP 10 分钟。转化频率与 cin 表达平行。暴露于 CSP 20 分钟后，两种 mRNA 几乎完全消失，这为关闭 CSP 信号转导的内在机制提供了证据。对混合培养物中自发感受态发育的研究表明，在 CSP 非产生菌存在的情况下，野生型细胞的转化被延迟，这与 CSP 在群体感应中的直接作用一致。研究了不同接种量对感受态发育时间的影响。虽然野生型培养物在相似的临界密度（约 OD550 = 0.15）下发展出感受态，但缺乏三种寡肽结合脂蛋白的突变体在细胞密度降低 50 倍时发生转化。在携带 comC 重复的菌株中模拟了后一种效应。总之，这些结果表明 CSP 不会在肺炎球菌培养物中被动积累，而是 comCDE 的基础表达可以被调节。
