In vivo transcription of the Escherichia coli oxyR regulon as a function of growth phase and in response to oxidative stress

Simultaneous expression of seven genes in Escherichia coli was measured by a reverse transcription-multiplex PCR fluorescence procedure. Genes studied were (i) oxyR (transcriptional regulator); (ii) katG, dps, gorA, and ahpCF (controlled by OxyR); (iii) sodA (controlled by SoxRS); and (iv) trxA (not related to OxyR or SoxRS). Except for trxA, transcription of all genes was activated during the course of growth of wild-type bacteria, though notabl e variations were observed,vith respect to both the time and extent of acti vation. Whereas oxyR, katG, dps, and gorA were activated during exponential growth, ahpCF and sodA, were stimulated in stationary phase. Maximal induc tion ranged from 4.6- to 86.5-fold, far gorA and dps, respectively. Treatme nt with H2O2 stimulated expression of the genes (katG, dps, ahpCF, and gorA ) previously identified as members of the OxyR regulon, except for oxyR its elf. Induction by H2O2 was a remarkably rapid and reversible process that t ook place in an OxyR-dependent and sigma(S)-independent manner. NaCl induce d expression of the genes controlled by OxyR, including the oxyR locus, Thi s transcriptional up-regulation was preserved in a strain with the Delta ox yR::kan mutation, but it was abolished (ahpCF) or significantly reduced (ox yR and dps) in a strain with the rpoS::Tn10 mutation, potentially reflectin g positive transcriptional regulation of the oxyR regulon by sigma(S). Expr ession of trxA was not increased either by H2O2 stress or by a shift to hig h-osmolarity conditions.