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J Bacteriol, June 1998, p. 2836-2841, Vol. 180, No. 11
Department of Microbiology and Infectious
Diseases, University of Calgary Health Sciences Center, Calgary,
Alberta, Canada T2N 4N1
Received 9 December 1997/Accepted 20 March 1998
The tolQRA genes have been recently identified in
Pseudomonas aeruginosa PAO. In this study, we examined the
effect of iron and temperature on tolQRA expression. A
promoterless lacZ gene was introduced downstream of
plasmid-encoded tolQ and tolA, and expression
was monitored by measuring
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Effects of Iron and Temperature on Expression of
the Pseudomonas aeruginosa tolQRA Genes: Role of the
Ferric Uptake Regulator
and
-galactosidase activity of
cultures. Addition of 25 µM FeCl3 to the culture
medium reduced tolQRA expression by 50 to 60% in PAO but
by only 25% in the fur mutant PAO A4. Northern
hybridization analysis revealed that iron regulation occurs at the
level of transcription and involves the P. aeruginosa
ferric uptake regulator (Fur). Primer extension analysis was
used to identify the proposed transcriptional start site of
tolA. Although a putative Fur box was identified 20 bp upstream of the proposed start site, purified Fur did not bind to the
tolA or tolQR promoter regions in an in vitro
gel retardation assay. Therefore, iron regulation of the
tol genes appears to involve an intermediate
regulatory gene. Expression of tolQR and tolA 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 reduced tolQR and
tolA expression.
*
Corresponding author. Mailing address: Department of
Microbiology and Infectious Diseases, University of Calgary Health
Sciences Center, 3330 Hospital Dr. NW, Calgary, Alberta, Canada
T2N 4N1. Phone: (403) 220-6037. Fax: (403) 270-2772. E-mail:
psokol{at}acs.ucalgary.ca.
Present address: Department of Microbiology, University of Texas
Southwestern Medical Center, Dallas, Tex.
J Bacteriol, June 1998, p. 2836-2841, Vol. 180, No. 11
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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