This page contains information about the plant-growth-promoting rhizobacterium (PGPR) Pseudomonas fluorescens Q8r1-96 that was isolated from a soil naturally suppressive to take-all disease of wheat (take-all decline, TAD) (1). TAD develops during wheat monoculture following a severe outbreak of take-all and results from the buildup of strains of Pseudomonas fluorescens that produce the antifungal metabolite 2,4-diacetylphloroglucinol (DAPG) (2). The unexpected finding that DAPG producers also are enriched in a pea wilt suppressive soil led us to characterize the genotypic and phenotypic relationships among isolates from fields that had experienced extended monoculture of wheat, peas, or flax (3, 4, 5). These studies resulted in the identification of a new class of "premier" PGPR - strains defined by DNA fingerprinting and exemplified by P. fluorescens Q8r1-96 from TAD soil (1).
 

Premier PGPR are minimally affected by soil type and environmental conditions, colonize roots consistently, and enhance plant growth when applied at low doses. These characteristics suggest that D-genotype strains differ fundamentally from other PGPR in their interaction with plant hosts, and that novel rhizosphere competence genes are responsible for these differences.

As a first step towards testing this hypothesis, we are studying various genomic clones from a Q8r1-96 library for their ability to enhance the rhizosphere competence of a closely-related but less aggressive root colonizer. We also are studying the role in rhizosphere competence of genes unique to premier PGPR. Finally, in order to evaluate the importance in premier strains of representative determinants previously implicated in the process of root colonization, we plan to create and determine the rhizosphere competence of defined mutants of strain Q8r1-96 defective in selected genes involved in motility, cell surface architecture, nutrient utilization, global gene regulation, and biofilm formation.

The relevant sequence information can be viewed, searched or analyzed (blast) online using MINE or Molecular INformation Explorer database. Please be sure to check the manual or FAQ if you have problems using the MINE's Search and Display Engine or any other script.

 

Epifluorescent microscopy of wheat roots colonized by Pseudomonas fluorescens Q8r1-96 tagged with green fluorescent protein. Wheat seeds were surface-sterilized, pre-germinated for 2 days and inoculated with a suspension of P.fluorescens Q8r1-96-gfp at 104 cfu/ml. Plants were grown in non-sterile soil and harvested 3 weeks after inoculation.

 

References

  1. Raaijmakers, J. M., and Weller, D. M. 2001. Exploiting the genetic diversity of Pseudomonas spp: characterization of superior colonizing P. fluorescens strain Q8r1-96. Appl. Environ. Microbiol.67:2545-2554.
  2. Raaijmakers, J. M., and Weller, D. M. 1998. Natural plant protection by 2,4-diacetylphloroglucinol-producing Pseudomonas spp. in take-all decline soils. Mol. Plant-Microbe Interact. 11:144-152.
  3. McSpadden Gardener, B. B., Schroeder, K. L., Kalloger, S. E., Raaijmakers, J. M., Thomashow, L. S., and Weller, D. M. 1999. Genotypic and phenotypic diversity of phlD-containing Pseudomonas isolated from the rhizosphere of wheat. Appl. Environ. Microbiol. 66:1939-1946.
  4. Mavrodi, O. V., B. B. McSpadden Gardener, D. V. Mavrodi, R. F. Bonsall, D. M. Weller, and L. S. Thomashow. 2001. Genetic diversity of phlD from 2,4-diacetylphloroglucinol-producing fluorescent Pseudomonas species. Phytopathology 91:35-43.
  5. Landa, B. B., Mavrodi, O. V., Raaijmakers, J. M., McSpadden Gardener, B. B., Thomashow, L. S., and Weller, D. M. 2002. Certain genotypes of 2,4-diacetylphloroglucinol-producing Pseudomonas fluorescens strains preferentially colonize the rhizosphere of pea. Appl. Environ. Microbiol. (in press)

 

                       

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