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Applied and Environmental Microbiology, March 2004, p. 1758-1766, Vol. 70, No. 3
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.3.1758-1766.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Positive Autoregulation and Signaling Properties of Pyoluteorin, an Antibiotic Produced by the Biological Control Organism Pseudomonas fluorescens Pf-5

Marion Brodhagen,1,{dagger} Marcella D. Henkels,2 and Joyce E. Loper1,2*

Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331,1 Horticultural Crops Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Corvallis, Oregon 973302

Received 15 May 2003/ Accepted 27 November 2003

Pseudomonas fluorescens Pf-5, a rhizosphere bacterium, produces a suite of secondary metabolites that are toxic to seed- and root-rotting plant pathogens. Among these are the polyketide compounds pyoluteorin and 2,4-diacetylphloroglucinol. We provide evidence that pyoluteorin production is influenced by positive autoregulation. Addition of pyoluteorin to liquid cultures of Pf-5 enhanced pyoluteorin production. In addition, pyoluteorin and 2,4-diacetylphloroglucinol mutually inhibit one another's production in Pf-5. For pyoluteorin, both positive autoregulation and negative influences on production by 2,4-diacetylphloroglucinol were demonstrated at the transcriptional level by measuring activity from transcriptional fusions of an ice nucleation reporter gene (inaZ) to three separate pyoluteorin biosynthetic genes. The occurrence of pyoluteorin autoregulation in the rhizosphere was assessed on cucumber seedlings in pasteurized soil with cross-feeding experiments. In the rhizosphere, expression of a pyoluteorin biosynthesis gene by a pyoluteorin-deficient mutant of Pf-5 was enhanced by pyoluteorin produced by coinoculated cells of Pf-5. These data establish that the polyketide pyoluteorin is an autoregulatory compound and functions as a signal molecule influencing the spectrum of secondary metabolites produced by the bacterial cell.

* Corresponding author. Mailing address: Agricultural Research Service, U.S. Department of Agriculture Horticultural Crops Research Laboratory, 3420 NW Orchard Ave., Corvallis, OR 97330. Phone: (541) 738-4057. Fax: (541) 738-4025. E-mail: loperj{at}mail.science.oregonstate.edu.

{dagger} Present address: Department of Microbiology, University of Washington, Seattle, WA 98195-7242.

Applied and Environmental Microbiology, March 2004, p. 1758-1766, Vol. 70, No. 3
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.3.1758-1766.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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