Differential expression of the transcription factors MarA, Rob, and SoxS of Salmonella Typhimurium in response to sodium
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ORIGINAL PAPER
Differential expression of the transcription factors MarA, Rob, and SoxS of Salmonella Typhimurium in response to sodium hypochlorite: down-regulation of rob by MarA and SoxS B. Collao • E. H. Morales • F. Gil • R. Polanco I. L. Caldero´n • C. P. Saavedra
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Received: 15 March 2012 / Revised: 1 June 2012 / Accepted: 8 June 2012 Ó Springer-Verlag 2012
Abstract To survive, Salmonella enterica serovar Typhimurium (S. Typhimurium) must sense signals found in phagocytic cells and modulate gene expression. In the present work, we evaluated the expression and cross-regulation of the transcription factors MarA, Rob, and SoxS in response to NaOCl. We generated strains DsoxS and DmarA, which were 20 times more sensitive to NaOCl as compared to the wild-type strain; while Drob only 5 times. Subsequently, we determined that marA and soxS transcript and protein levels were increased while those of rob decreased in a wild-type strain treated with NaOCl. To assess if changes in S. Typhimurium after exposure to NaOCl were due to a cross-regulation, as in Escherichia coli, we evaluated the expression of marA, soxS, and rob in the different genetic backgrounds. The positive regulation observed in the wild-type strain of marA and soxS was retained in the Drob strain. As in the wild-type strain, rob was down-regulated in the DmarA and DsoxS treated with NaOCl; however, this effect was decreased. Since rob was down-regulated by both factors, we generated a DmarA DsoxS strain finding that the negative regulation was abolished, confirming our hypothesis. Electrophoretic B. Collao and E. H. Morales contributed equally to this article. Communicated by Jan Roelof van der Meer. B. Collao E. H. Morales F. Gil I. L. Caldero´n C. P. Saavedra (&) Laboratorio de Microbiologı´a Molecular, Facultad de Ciencias Biolo´gicas, Universidad Andres Bello, Repu´blica 217, Santiago, Chile e-mail: [email protected] R. Polanco Laboratorio de Bioquı´mica, Departamento de Ciencias Biolo´gicas, Universidad Andres Bello, Santiago, Chile
mobility shift assays using MarA and SoxS confirmed an interaction with the promoter of rob. Keywords marA/rob/soxS regulon Oxidative stress Sodium hypochlorite
Introduction Hypochlorous acid (HOCl) is a highly reactive oxygen species (ROS) produced by the action of myeloperoxidase (MPO) in a reaction that depends on H2O2, Cl-, and acidic conditions (Thomas 1979; Rosen et al. 2002). With the exception of macrophages, all phagocytic cells show detectable levels of MPO (Hassett and Cohen 1989). HOCl reacts with a wide range of cellular components causing (1) sulfhydryl oxidation, (2) inactivation of iron–sulfur centers, (3) inactivation of enzymes involved in respiration, (4) disruption of nutrient transport, (5) inhibition of energy generation, and (6) inactivation of chromosomal DNA replication (Khan and Kasha 1994; Leyer and Johnson 1997; Mokgatla et al. 2002). Resistance to HOCl is thought to depend on similar molecular mechanisms as those described for hydrogen peroxide. Escherichia coli mutants
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