ABSTRACT: The GntR-like protein NorG has been shown to affect Staphylococcus aureus genes involved in the resistance to quinolones and beta-lactams such as those encoding the NorB and AbcA transporters. To identify the target genes regulated by NorG, we carried out transcriptional profiling assays using S. aureus RN6390 and its isogenic norG::cat mutant. Our data showed that NorG positively affected the transcription of global regulators mgrA, arlS, and sarZ. The three putative drug efflux pump genes most positively affected by NorG were the NorB efflux pump (5.1-fold), the MmpL-like protein SACOL2566 (5.2-fold), and the BcrA-like drug transporter SACOL2525 (5.7-fold). The S. aureus predicted MmpL protein showed 53% homology with the MmpL lipid transporter of Mycobacterium tuberculosis, and the putative SACOL2525 protein showed 87% homology with the bacitracin drug transporter BcrA of Staphylococcus hominis. Two pump genes most negatively affected by NorG were NorC (4-fold) and AbcA (6-fold). Other categories of genes such as those participating in amino acid, inorganic ion, or nucleotide transporters and metabolism, were also affected by NorG. Real-time RT-PCR assays for mgrA, arlS, sarZ, norB, norC, abcA, mmpL, and bcrA-like were carried out to verify microarray data and showed the same level of up- or down regulation by NorG. The norG mutant showed a twofold increase in the resistance to norfloxacin and rhodamine, both substrates of the NorC transporter, which is consistent with the resistance phenotype conferred by overexpression of norC on a plasmid. These data indicate that NorG has broad regulatory function in S. aureus. The goal of this study was to define the transcriptional response of S. aureus norG mutant cells. To do so, commercially available S. aureus Affymetrix GeneChips (Santa Clara, CA) were used to compare the expression properties of wild type (ISP794) and isogenic norG (QT11) mutant cells. S. aureus strains ISP794 and QT11 were grown to mid exponential phase growth, lysed , total bacterial RNA was extracted, labeled and hybridized to commerically available S. aureus Affymetrix GeneChips. In total three biological replicates were compared for each strain background.
