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Journal of Bacteriology, October 1999, p. 6152-6159, Vol. 181, No. 19
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Identification of a Regulator That Controls Stationary-Phase Expression of Catalase-Peroxidase in Caulobacter crescentus

Paul S. Rava, Laura Somma, and Howard M. Steinman*

Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461

Received 3 June 1999/Accepted 27 July 1999

Expression of the catalase-peroxidase of Caulobacter crescentus, a gram-negative member of the alpha  subdivision of the Proteobacteria, is 50-fold higher in stationary-phase cultures than in exponential cultures. To identify regulators of the starvation response, Tn5 insertion mutants were isolated with reduced expression of a katG::lacZ fusion on glucose starvation. One insertion interrupted an open reading frame encoding a protein with significant amino acid sequence identity to TipA, a helix-turn-helix transcriptional activator in the response of Streptomyces lividans to the peptide antibiotic thiostrepton, and lesser sequence similarity to other helix-turn-helix regulators in the MerR family. The C. crescentus orthologue of tipA was named skgA (stationary-phase regulation of katG). Stationary-phase expression of katG was reduced by 70% in the skgA::Tn5 mutant, and stationary-phase resistance to hydrogen peroxide decreased by a factor of 10. Like the wild type, the skgA mutant exhibited starvation-induced cross-resistance to heat and acid shock, entered into the helical morphology that occurs after 9 to 12 days in stationary phase, and during exponential growth induced katG in response to hydrogen peroxide challenge. Expression of skgA increased 5- to 10-fold in late exponential phase. skgA is the first regulator of a starvation-induced stress response identified in C. crescentus. SkgA is not a global regulator of the stationary-phase stress response; its action encompasses the oxidative stress-hydrogen peroxide response but not acid or heat responses. Moreover, SkgA is not an alternative sigma  factor, like RpoS, which controls multiple aspects of starvation-induced cross-resistance to stress in enteric bacteria. These observations raise the possibility that regulation of stationary-phase gene expression in this member of the alpha  subdivision of the Proteobacteria is different from that in Escherichia coli and other members of the gamma  subdivision.


* Corresponding author. Mailing address: Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-3010. Fax: (718) 430-8565. E-mail: steinman{at}aecom.yu.edu.


Journal of Bacteriology, October 1999, p. 6152-6159, Vol. 181, No. 19
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.



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