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Applied and Environmental Microbiology, June 1999, p. 2294-2299, Vol. 65, No. 6
Department of Plant Pathology, University of
Arizona, Tucson, Arizona 85721,1 and
Department of Microbiology, University of Washington, Seattle,
Washington 981952
Received 8 January 1999/Accepted 17 March 1999
Production of phenazine antibiotics by the biological control
bacterium Pseudomonas aureofaciens 30-84 is regulated in
part by the PhzI/PhzR N-acyl-homoserine lactone (AHL)
response system (L. S. Pierson III, V. D. Keppenne, and
D. W. Wood, J. Bacteriol. 176:3966-3974, 1994; D. W. Wood
and L. S. Pierson III, Gene 168:49-53, 1996). Two mutants, 30-84W
and 30-84.A2, were isolated and were found to be deficient in the
production of phenazine, protease, hydrogen cyanide (HCN), and the AHL
signal N-hexanoyl-homoserine lactone. These mutants were
not complemented by phzI, phzR, or the
phenazine biosynthetic genes (phzFABCD) (L. S. Pierson
III, T. Gaffney, S. Lam, and F. Gong, FEMS Microbiol. Lett.
134:299-307, 1995). A 2.2-kb region of the 30-84 chromosome which
fully restored production of all of these compounds in strain 30-84W
was identified. Nucleotide sequence analysis of this region revealed a
single open reading frame encoding a predicted 213-amino-acid protein which is very similar to the global response regulator GacA. Strain 30-84.A2 was not complemented by gacA or any cosmid from a
genomic library of strain 30-84 but was complemented by
gacS (formerly lemA) homologs from
Pseudomonas fluorescens Pf-5 (N. Corbel and J. E. Loper, J. Bacteriol. 177:6230-6236, 1995) and Pseudomonas syringae pv. syringae B728a (E. M. Hrabek and D. K. Willis, J. Bacteriol. 174:3011-3020, 1992). Transcription of
phzR was not altered in either mutant; however,
phzI transcription was eliminated in strains 30-84W and
30-84.A2. These results indicated that the GacS/GacA two-component
signal transduction system of P. aureofaciens 30-84 controls the production of AHL required for phenazine production by
mediating the transcription of phzI. Addition of exogenous AHL did not complement either mutant for phenazine production, indicating that the GacS/GacA global regulatory system controls phenazine production at multiple levels. Our results reveal for the
first time a mechanism by which a two-component regulatory system and
an AHL-mediated regulatory system interact.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Two-Component Transcriptional Regulation of
N-Acyl-Homoserine Lactone Production in
Pseudomonas aureofaciens
*
Corresponding author. Mailing address: Department of
Plant Pathology, University of Arizona, Tucson, AZ 85721. Phone: (520) 621-9419. Fax: (520) 621-9290. E-mail:
LSP{at}u.arizona.edu.
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