Transcription Modulation of Salmonella enterica Serovar Typhimurium Promoters by Sub-MIC Levels of Rifampin

Promoter-lux fusions that showed rifampin-modulated transcription were identified from a Salmonella enterica serovar Typhimurium 14028 reporter library. The transformation of a subset of fusions into mutants that lacked one of six global regulatory proteins or were rifampin resistant showed that transcription modu-lation was independent of the global regulators, promoter specific, and dependent on the interaction of rifampin with RNA polymerase. Antibiotics have been shown to alter global bacterial tran-scription patterns at concentrations below those that com-pletely inhibit the growth of the bacterial cell (sub-MIC) (10, 29). Among the genes affected by antibiotics are those related to modes of action and bacterial stress responses. It has been suggested that characteristic gene expression patterns may be used to identify unknown small molecule inhibitors (2, 28). There have also been studies demonstrating antibiotic-induced transcription modulation of genes for accessory functions such as motility and virulence (reviewed in references 2 and 29). Using a library of 6,528 promoter-reporter clones, we pre-viously demonstrated dramatic up- and down-regulation of th