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Journal of Bacteriology, December 1998, p. 6635-6641, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Two-Component Regulators GacS and GacA Influence Accumulation of the Stationary-Phase Sigma Factor sigma S and the Stress Response in Pseudomonas fluorescens Pf-5

Cheryl A. Whistler,1 Nathan A. Corbell,2 Alain Sarniguet,3 Walter Ream,4 and Joyce E. Loper2,5,*

Molecular and Cellular Biology Program,1 Department of Botany and Plant Pathology,2 and Department of Microbiology,4 Oregon State University, Corvallis, Oregon 97331; Institut National de la Recherche Agronomique, Station de Pathologie Vegetale, Centre de Recherche de Rennes, 35653 Le Rheu Cedex, France3; and Agricultural Research Service, U.S. Department of Agriculture, Corvallis, Oregon 973305

Received 4 June 1998/Accepted 26 September 1998

Three global regulators are known to control antibiotic production by Pseudomonas fluorescens. A two-component regulatory system comprised of the sensor kinase GacS (previously called ApdA or LemA) and GacA, a member of the FixJ family of response regulators, is required for antibiotic production. A mutation in rpoS, which encodes the stationary-phase sigma factor sigma S, differentially affects antibiotic production and reduces the capacity of stationary-phase cells of P. fluorescens to survive exposure to oxidative stress. The gacA gene of P. fluorescens Pf-5 was isolated, and the influence of gacS and gacA on rpoS transcription, sigma S levels, and oxidative stress response of Pf-5 was determined. We selected a gacA mutant of Pf-5 that contained a single nucleotide substitution within a predicted alpha -helical region, which is highly conserved among the FixJ family of response regulators. At the entrance to stationary phase, sigma S content in gacS and gacA mutants of Pf-5 was less than 20% of the wild-type level. Transcription of rpoS, assessed with an rpoS-lacZ transcriptional fusion, was positively influenced by GacS and GacA, an effect that was most evident at the transition between exponential growth and stationary phase. Mutations in gacS and gacA compromised the capacity of stationary-phase cells of Pf-5 to survive exposure to oxidative stress. The results of this study provide evidence for the predominant roles of GacS and GacA in the regulatory cascade controlling stress response and antifungal metabolite production in P. fluorescens.

* Corresponding author. Mailing address: Horticultural Crops Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 3420 N.W. Orchard Ave., Corvallis, OR 97330. Phone: (541) 750-8771. Fax: (541) 750-8764. E-mail: loperj{at}bcc.orst.edu.

Journal of Bacteriology, December 1998, p. 6635-6641, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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