Competence regulation by oxygen in <i>Streptococcus pneumoniae</i>: involvement of <i>ciaRH</i> and <i>comCDE</i>

Abstract

Anaerobic aerotolerant Streptococcus pneumoniae modulates its genetic transformability and its virulence in response to the oxygen concentration. The activity of a single protein encoded by nox and showing NADH oxidase activity is involved in these adaptive responses to O 2 . Northern blot analysis of wild‐type cultures grown under aerobic and microaerobic conditions indicated transcriptional control of comCDE by O 2 . An O 2 ‐independent mutant strain carrying the gain‐of‐function mutation comE38KE was isolated and its analysis showed that ComE is a key point in competence stimulation by O 2 . Plasmid insertion mutations in ciaRH revealed that this two component signal‐transducing system negatively regulates comCDE transcription. The level of comCDE transcripts appears as a major control point in competence regulation by O 2 and also by growth phase and cell density.