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ThetolQRA genes have been recently identified inPseudomonas aeruginosa PAO. In this study, we examined the effect of iron and temperature ontolQRA expression. A promoterlesslacZ gene was introduced downstream of plasmid-encodedtolQ andtolA , and expression was monitored by measuring β-galactosidase activity of cultures. Addition of 25 μM FeCl3 to the culture medium reducedtolQRA expression by 50 to 60% in PAO but by only 25% in thefur mutant PAO A4. Northern hybridization analysis revealed that iron regulation occurs at the level of transcription and involves theP. aeruginosa ferric uptake regulator (Fur). Primer extension analysis was used to identify the proposed transcriptional start site oftolA . Although a putative Fur box was identified 20 bp upstream of the proposed start site, purified Fur did not bind to thetolA ortolQR promoter regions in an in vitro gel retardation assay. Therefore, iron regulation of thetol genes appears to involve an intermediate regulatory gene. Expression oftolQR andtolA was optimal at 37°C and was reduced by 40 to 50% when cultures were grown at either 42 or 25°C. Growth in high-iron medium at 25°C further reducedtolQR andtolA expression.

Effects of Iron and Temperature on Expression of the Pseudomonas aeruginosa tolQRA Genes: Role of the Ferric Uptake Regulator