mgtA expression is induced by Rob and mediates Salmonella cyclohexane resistance

JULIETA BARCHIESI; MARÍA EUGENIA CASTELLI; FERNANDO C. SONCINI; ELEONORA GARCÍA VÉSCOVI

Villa Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual; 2008

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

mgtA codes for a P-type ATPase which is known as one of the three Mg2+ transporters in Salmonella enterica, It has been previously demonstrated that mgtA expression is regulated at the transcriptional level by the extracellular Mg2+-responsive PhoP/PhoQ two-component system and post-transcriptionally by an intracellular Mg2+-sensitive riboswitch. In our laboratory, while searching for factors that would modulate the expression of Salmonella mgtA, independently of the PhoP/PhoQ system, we identified Rob. Rob is a member of the a subfamiliy of AraC/XylStype transcriptional regulators implicated in bacterial multidrug, heavy metal, superoxide and organic solvent resistance phenotypes. We demonstrate that, in Salmonella, Rob expression (but not its paralog proteins SoxS or MarA) is able to induce mgtA transcription in a PhoP-independent fashion by binding to a conserved rob/mar/sox motif localized downstream the PhoP-box, and overlapping the PhoP-dependent transcriptional start site. We found that Rob-induced mgtA expression confers Salmonella a low-level cyclohexane resistance. Because mgtA intactness is required for Rob-induced cyclohexane resistance provided the AcrAB multidrug efflux pump can be expressed, we postulate that MgtA is involved in the AcrAB-mediated cyclohexane detoxification mechanism promoted by Rob expression, disclosing a novel role for MgtA in Salmonella.