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Applied and Environmental Microbiology, November 2006, p. 7111-7122, Vol. 72, No. 11
0099-2240/06/$08.00+0     doi:10.1128/AEM.01215-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Role of ptsP, orfT, and sss Recombinase Genes in Root Colonization by Pseudomonas fluorescens Q8r1-96{triangledown}

Olga V. Mavrodi,1 Dmitri V. Mavrodi,1 David M. Weller,2 and Linda S. Thomashow2*

Department of Plant Pathology, Washington State University, Pullman, Washington,1 USDA-ARS, Root Disease and Biological Control Research Unit, Pullman, Washington2

Received 26 May 2006/ Accepted 13 August 2006

Pseudomonas fluorescens Q8r1-96 produces 2,4-diacetylphloroglucinol (2,4-DAPG), a polyketide antibiotic that suppresses a wide variety of soilborne fungal pathogens, including Gaeumannomyces graminis var. tritici, which causes take-all disease of wheat. Strain Q8r1-96 is representative of the D-genotype of 2,4-DAPG producers, which are exceptional because of their ability to aggressively colonize and maintain large populations on the roots of host plants, including wheat, pea, and sugar beet. In this study, three genes, an sss recombinase gene, ptsP, and orfT, which are important in the interaction of Pseudomonas spp. with various hosts, were investigated to determine their contributions to the unusual colonization properties of strain Q8r1-96. The sss recombinase and ptsP genes influence global processes, including phenotypic plasticity and organic nitrogen utilization, respectively. The orfT gene contributes to the pathogenicity of Pseudomonas aeruginosa in plants and animals and is conserved among saprophytic rhizosphere pseudomonads, but its function is unknown. Clones containing these genes were identified in a Q8r1-96 genomic library, sequenced, and used to construct gene replacement mutants of Q8r1-96. Mutants were characterized to determine their 2,4-DAPG production, motility, fluorescence, colony morphology, exoprotease and hydrogen cyanide (HCN) production, carbon and nitrogen utilization, and ability to colonize the rhizosphere of wheat grown in natural soil. The ptsP mutant was impaired in wheat root colonization, whereas mutants with mutations in the sss recombinase gene and orfT were not. However, all three mutants were less competitive than wild-type P. fluorescens Q8r1-96 in the wheat rhizosphere when they were introduced into the soil by paired inoculation with the parental strain.

* Corresponding author. Mailing address: USDA-ARS Root Disease & Biological Control Research Unit, Washington State University, Pullman, WA 99164-6430. Phone: (509) 335-0930. Fax: (509) 335-7674. E-mail: thomasho{at}mail.wsu.edu.

{triangledown} Published ahead of print on 25 August 2006.

Applied and Environmental Microbiology, November 2006, p. 7111-7122, Vol. 72, No. 11
0099-2240/06/$08.00+0     doi:10.1128/AEM.01215-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Huang, J., Xu, Y., Zhang, H., Li, Y., Huang, X., Ren, B., Zhang, X. (2009). Temperature-Dependent Expression of phzM and Its Regulatory Genes lasI and ptsP in Rhizosphere Isolate Pseudomonas sp. Strain M18. Appl. Environ. Microbiol. 75: 6568-6580 [Abstract] [Full Text]  


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