Inhibition of competence development in Streptococcus pneumoniae by increased basal-level expression of the ComDE two-component regulatory system.
Natural competence for genetic transformation in Streptococcus pneumoniae is controlled by the ComCDE signal-transduction pathway. Together, ComD, a membrane histidine kinase, and ComE, its cognate response regulator, constitute a typical two-component regulatory system involved in sensing the comC-encoded competence-stimulating peptide (CSP). The comCDE operon is strongly upregulated when CSP reaches a critical threshold, probably to coordinate competence induction throughout the population. During a study of the early regulation of the comCDE operon, a mutation which resulted in increased beta-galactosidase production from a comC : : lacZ fusion was isolated. This mutation, which was characterized as a G-->T change in the transcription terminator of the tRNA(Arg) located immediately upstream of comCDE, is suggested to destabilize the terminator and to allow transcriptional readthrough of comCDE. Here, it is shown that, quite unexpectedly, the mutation confers reduced transformability. A series of experiments undertaken with the aim of understanding this surprising phenotype is described. Evidence is presented that increased basal-level expression of comDE impedes both spontaneous and CSP-induced competence in S. pneumoniae. There is a discussion of how an increased concentration of ComD and/or ComE could affect competence development.
Guiral
Sébastien
S
Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Hénard
Vincent
V
Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Granadel
Chantal
C
Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Martin
Bernard
B
Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Claverys
Jean-Pierre
JP
Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D000071677:Histidine Kinase; D009154:Mutation; D009876:Operon / Q000235:genetics*; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D013296:Streptococcus pneumoniae / Q000235:genetics* / Q000378:metabolism; D014169:Transformation, Bacterial
D001426:Bacterial Proteins; D011494:Protein Kinases; D000071677:Histidine Kinase