LadR, a new PadR-related transcriptional regulator from Listeria monocytogenes, negatively regulates the expression of the multidrug efflux pump MdrL.

The Listeria monocytogenes genome encodes putative multidrug efflux transporters but only the MdrL transporter has been partially characterized in the wild-type LO28 strain. Here, we show in the LO28 strain, that the expression of MdrL is repressed at the transcriptional level, under standard growth conditions, by the product of a new gene ladR (lmo1408), and the expression of MdrL is induced in the presence of rhodamine. Phylogenetic analysis in related firmicutes shows that LadR, conserved in all sequenced Listeria genomes, forms an independent group from the large and diverse PadR transcriptional regulator family (PF03551). This is the first report of a bacterial multidrug transporter controlled by a member of the PadR family.