[ODP-057/WS6-7] Analysis of regulatory mechanisms of novel Toxin-antitoxin systems found in EHEC O157 Sakai
Toxin-antitoxin systems (TA systems) are generally found in bacterial genomes. Activation of toxin by inactivation of antitoxin induces growth arrest or cell death, through inhibiting fundamental cellular processes. We have found a novel Type 2 TA system (ECs5400-5399) in EHEC O157 Sakai. The toxin gene (ECs5400) is predicted to encode a ribonuclease. Previously, we showed that over-expression of the toxin gene reduced the growth of EHEC. At low expression levels, the toxin gene preferentially reduced the production of virulence factors. In this study, we explored the role of Antitoxin in regulation of this TA systems genes. Induction of ECs5399 (antitoxin gene) markedly reduced the promoter activity. Additionally, we showed the binding of antitoxin (ECs5399) protein to the promoter region. These results indicated that ECs5399 antitoxin protein is a repressor of ECs5400-5399 operon as reported for the other antitoxins of type 2 TA systems. We further explore the conditions affecting the promoter activity and found that the promoter activity was increased in the late log phase of growth in rpoS-dependent manner. In addition, the increase of the promoter activity was abrogated by lon deletion mutant. These results suggested that the toxin of ECs5400-5399 operon might be activated by stress signals inducing Lon protease and RNA polymerase with sigma S.