Page Banner

United States Department of Agriculture

Agricultural Research Service

Information on Strain Pf-5
headline bar

 

 

 

Pseudomonas fluorescens Pf-5

 

Pf-5 suppresses many soilborne plant diseases

Pf-5 produces a broad spectrum of antibiotics

Regulation of antibiotic production in Pf-5

Pf-5 is representative of other important biological control strains

Pseudomonas spp. as biological control agents

Reference list

 

Pseudomonas fluorescens Pf-5 inhabits the root surfaces (rhizosphere) of many plants and functions as a biological control agent, suppressing a number of plant diseases caused by soilborne plant pathogens. Pf-5 produces a large spectrum of secondary metabolites, including several antibiotics. The selection of P. fluorescens Pf-5 as the subject for genomic sequencing was based upon the importance of Pf-5 as a biological control organism, its rhizosphere competence, the large spectrum of antibiotics and other secondary metabolites that it produces, and its status as model environmental strain for studies of gene regulation. Strain Pf-5 was described early in the history of biological control research (Howell and Stipanovic 1979, 1980), and it was the first biological control agent for which the chemical basis of disease suppression was known.

 

Pf-5 suppresses many soilborne plant diseases

Pf-5 was first described for its capacity to suppress soilborne diseases of cotton caused by Rhizoctonia solani (Howell and Stipanovic, 1979) and Pythium ultimum (Howell and Stipanovic, 1980). These pathogens are the major cause of seed rot and seedling death throughout much of the Cotton Belt in the USA. Seedling diseases caused an estimated loss of 828,000 bales of cotton nationwide in 1995, with similar losses in previous years. R. solani and P. ultimum are widespread pathogens with broad host ranges that constrain food and fiber production worldwide (Martin and Loper, 1999). Since it was first described, Pf-5 has been shown to suppress these pathogens on plant hosts including cucumber, pea, and maize (Kraus and Loper, 1992; Henkels and Loper, unpublished). Furthermore, Pf-5 suppresses a number of other soilborne or residue-borne fungal pathogens. When inoculated onto wheat straw residue, Pf-5 suppresses ascocarp formation by the tan spot pathogen of wheat, Pyrenophora tritici-repentis, thereby decreasing inoculum available for infection of the subsequent wheat crop (Pfender et al., 1993). On turfgrass, Pf-5 suppresses dollar spot caused by Sclerotinia homoeocarpa and leaf spot caused by Dreschslera poae, which are destructive and widespread diseases affecting golf courses, home lawns, and amenity turf areas (Rodriguez and Pfender, 1997). Pf-5 also suppresses Fusarium crown and root rot of tomato, caused by Fusarium oxysporum f. sp. radicis-lycopersici (Sharifi-Tehrani et al., 1998) and seed piece decay of potato caused by the bacterial pathogen Erwinia carotovora (Xu and Gross,1986).
Because of the wide variety of diseases suppressed by Pf-5, it is well-recognized by biological control researchers around the world. Pf-5 commonly is included as a reference strain in studies of biocontrol agents (as examples, see Keel et al., 1996; Kloepper, 1991; McSpadden-Gardener et al., 2000; Sharifi-Tehrani et al., 1998; and Xu and Gross, 1996).

 

Pf-5 produces a broad spectrum of antibiotics

Pf-5 produces a suite of antibiotics including pyrrolnitrin, pyoluteorin, and 2,4-diacetylphloroglucinol; it also produces hydrogen cyanide and the siderophores pyochelin and pyoverdine. Each of these compounds has a different spectrum of activity against plant pathogens, and their roles in biological control have been established in various biological control organisms. The spectrum of antibiotics produced by Pf-5 is remarkably similar to that produced by another well-known biological control strain, P. fluorescens CHA0, which was isolated in Switzerland (Stutz et al.1986).
The genetics of pyoluteorin production has been investigated in strain Pf-5. Pyoluteorin is composed of a resorcinol ring linked to a bichlorinated pyrrole moiety. It inhibits the growth of Oomycetes, including plant pathogens in the genus Pythium (Howell and Stipanovic, 1980). Pyoluteorin is derived from proline, the primary precursor to the dichloropyrrole ring, and three molecules of acetyl-coA, which are incorporated into the resorcinol ring via a polyketide mechanism of biosynthesis (Nowak-Thompson, 1997). 24-kb of the pyoluteorin gene cluster in strain Pf-5 has been sequenced and the deduced protein products of identified ORFs correspond logically to the proposed biochemical transformations required for pyoluteorin synthesis (Nowak-Thompson et al., 1997, 1999). Halogenation of the pyrrole ring in pyoluteorin appears to involve the pyoluteorin biosynthetic genes pltA, pltD, and pltM. These genes encode members of a newly-described class of enzymes that chlorinate secondary metabolites, a function previously ascribed to haloperoxidases. Unlike the synthases that participate in the well-described pathways for polyketide synthesis in actinomycetes, a combination of mono- and multi-functional enzymes appears to be responsible for the synthesis of the resorcinol moiety of pyoluteorin (Nowak-Thompson et al., 1997, 1999). Thus, the biosynthetic gene cluster for pyoluteorin offers some striking contrasts to the general classes of polyketide synthases and chlorinating enzymes established for gram-positive microorganisms.

 

Regulation of antibiotic production in Pf-5

Regulation of antifungal metabolite production by biological control strains of Pseudomonas spp. is controlled by complex regulatory networks that respond to environmental and density-dependent signals and are coupled to the physiological status of the bacterium). Loci that regulate the production of antifungal metabolites in Pf-5 and the closely-related strain CHA0 include a two-component regulatory system encoded by gacS and gacA (Corbell and Loper, 1995; Gaffney et al., 1994; Laville et al., 1992), the sigma factors S (Sarniguet et al., 1995) and 70 (Schnider et al., 1994), the cofactor PQQ (Schnider et al., 1995), the anaerobic regulator anr (Laville et al., 1998) the protease Lon (Whistler et al., 2000) and ptsP, a paralog of sugar phosphotransferase enzyme I (Whistler, 2000). Many of these loci control multiple phenotypes including stress response in P. fluorescens (Sarniguet et al., 1995; Whistler et al., 1998, 2000), indicating that regulation of antibiotic production is intricately enmeshed in the physiology of the bacterial cell.

 

Pf-5 is representative of other important biological control strains

Biological control strains of P. fluorescens have been isolated from soils and plant surfaces all over the world, and they comprise a diverse group of environmental isolates. Nevertheless, biological control strains do fall into groups defined by biochemical and molecular criteria. Studies evaluating collections of biocontrol strains by BOX- and ERIC-PCR (McSpadden-Gardener et al., 2000) or restriction analysis of amplified spacer ribosomal DNA (Keel et al., 1996; Sharifi-Tehrani et al, 1996) consistently place Pf-5 in a group with CHA0 and other pyoluteorin and phloroglucinol-producng biocontrol strains.

 

Pseudomonas spp. as biological control agents

Throughout the history of agriculture, humans have struggled to reduce the adverse effects of plant disease on their crops. Early agriculturalists realized the benefits of cultural practices such as crop rotation and the use of organic soil amendments in promoting plant productivity. It is now well established that many of these effects are achieved by promoting the natural microbiological processes that keep plant disease in check. Cultural practices were mainstays of traditional agricultural systems and still provide the primary approaches for management of many soilborne diseases today. For example, disease suppressive soils, into which pathogen(s) can be introduced without causing the expected levels of disease severity, can result from alterations in cropping patterns or other cultural practices. Recently, Pseudomonas spp. that produce a specific antibiotic have been associated convincingly with soil suppressiveness. This compelling evidence for the role of Pseudomonas spp. in natural processes of biological control has built even greater enthusiasm for the development of these bacteria as biological control agents.

 

The potential of specific strains of Pseudomonas spp. for suppression of plant disease in agriculture has been demonstrated in hundreds, if not thousands, of experiments worldwide. Typically, a collection of strains isolated at random from plant surfaces are inoculated individually onto seeds, roots, or aerial plant tissues, and inoculated plants are compared to non-inoculated plants in disease assays. Over and over again, Pseudomonas spp. have been identified for their suppressive effects on plant pathogens in these studies. For example, in greenhouse studies in which a random collection of culturable bacteria were screened directly for suppression of Pythium damping-off, fluorescent pseudomonads comprised a large proportion (33% to 100%) of the effective biocontrol strains (Loper, 1988). There is no question that strains representing diverse genera of Gram-negative and Gram-positive bacteria can suppress plant disease, but fluorescent pseudomonads are typically among the most effective antagonists selected for suppression of both soilborne and aerial diseases of plants (Loper et al., 1997). Approximately one third of the articles coded for the subjects of biological control and plant disease in the Agricola database involve Pseudomonas spp. Therefore, the genus has been the focus of ecological and mechanistic research evaluating biological control of plant disease.

 

Top of page

Reference list

  • Corbell, N. and J. E. Loper. 1995. A global regulator of secondary metabolite production in Pseudomonas fluorescens Pf-5. J. Bacteriol. 177:6230-6236.
  • Gaffney, T. D., S. T. Lam, K. Gates, A. Frazelle, J. Di Maio, S. Hill, S. Goodwin, N. Torkewitz, A. M. Allshouse, H. J. Kempf, and J. O. Becker. 1994. Global regulation of expression of anti-fungal factors by a Pseudomonas fluorescens biological control strain. Mol. Plant-Microbe Interact. 7:455-463.
  • Howell, C. R. and R. D. Stipanovic . 1979. Control of Rhizoctonia solani in cotton seedlings with Pseudomonas fluorescens and with an antibiotic produced by the bacterium. Phytopathology 69:480-482.
  • Howell, C. R. and R. D. Stipanovic. 1980. Suppression of Pythium ultimum induced damping-off of cotton seedlings by Pseudomonas fluorescens and its antibiotic pyoluteorin. Phytopathology 70:712-715.
  • Keel, C., D. M. Weller, A. Natsch, G. Defago, R. J. Cook, and L. S. Thomashow. 1996. Conservation of the 2,4-diacetylphloroglucinol biosynthesis locus among fluorescent Pseudomonas strains from diverse geographic locations. Appl. Environ. Microbiol. 62:552-563.
  • Kloepper, J. W. 1991. Development of in vivo assays for prescreening antagonists of Rhizoctonia solani on cotton. Phytopathology 81:1006-1013.
    Kraus, J. and J. E. Loper. 1992. Lack of evidence for a role of antifungal metabolite production by Pseudomonas fluorescens Pf-5 in biological control of pythium damping-off of cucumber. Phytopathology 82:264-271.
  • Laville, J., C. Voisard, C. Keel, M. Maurhofer, G. Defago,and D. Haas. 1992. Global control in Pseudomonas fluorescens mediating antibiotic synthesis and suppression of black root rot of tobacco. Proc. Natl. Acad. Sci. USA 89:1562-1566.
  • Laville, J., C. Blumer, C. Von Schroetter, V. Gaia, G. Defago, C. Keel, and D. Haas. 1998. Characterization of the hcnABC gene cluster encoding hydrogen cyanide synthase and anaerobic regulation by ANR in the strictly aerobic biocontrol agent Pseudomonas fluorescens CHA0. J. Bacteriol. 180:3187-3196.
  • Loper, J. E. 1988. Role of fluorescent siderophore production in biological control of Pythium ultimum by a Pseudomonas fluorescens strain. Phytopathology 78: 166-172.
  • Loper, J. E., Nowak-Thompson, B., Whistler, C. A., Hagen, M. J., Corbell, N. A., Henkels, M. D, and Stockwell, V. O. 1997. Pages 73-79 in: Biological control mediated by antifungal metabolite production and resource competition: an overview. Ogoshi, A., Kobayashi., K., Homma, Y., Kodama, F., Kondo, N., and Akino, S. Proceedings of the Fourth International Workshop on Plant Growth Promoting Rhizobacteria.
  • Martin, F. N. and J. E. Loper. 1999. Soilborne plant diseases caused by Pythium spp.: Ecology, epidemiology, and prospects for biological control. Critical Reviews in Plant Sciences 18:111-181.
  • McSpadden-Gardener, B. B., K. L. Schroeder, S. E. Kalloger, J. M. Raaijmakers, L. S. Thomashow, and D. M. Weller. 2000. Genotypic and phenotypic diversity of phlD-containing Pseudomonas strains isolated from the rhizosphere of wheat. Appl Environ Microbiol. 66:1939-1946.
  • Nowak-Thompson, B., N. Chaney, J. S. Wing, S. J. Gould, and J. E. Loper. 1999. Characterization of the pyoluteorin biosynthetic gene cluster of Pseudomonas fluorescens Pf-5. J. Bacteriol. 181:2166-2174.
  • Nowak-Thompson, B., S. J. Gould, and J. E. Loper. 1997. Identification and sequence analysis of the genes encoding a polyketide synthase required for pyoluteorin biosynthesis in Pseudomonas fluorescens Pf-56. Gene 204:17-24.
  • Pfender, W. F., J. Kraus, and J. E. Loper. 1993. A genomic region from Pseudomonas fluorescens Pf-5 required for pyrrolnitrin production and inhibition of Pyrenophora tritici-repentis in wheat straw. Phytopathology 83:1223-1228.
  • Rodriguez, F. and W. F. Pfender. 1997. Antibiosis and antagonism of Sclerotinia homoeocarpa and Drechslera poae by Pseudomonas fluorescens Pf-5 in vitro and in planta. Phytopathology 87:614-621.
  • Sarniguet, A., J. Kraus, M. D. Henkels, A. M. Muehlchen, and J. E. Loper. 1995. The sigma factor RpoS affects antibiotic production and biological control activity of Pseudomonas fluorescens Pf-5. Proc. Natl. Acad. Sci. U. S. A. 92:12255-12259.
  • Schnider, U.; Keel, C.; Voisard, C.; Défago, G., and Haas, D. 1995. Tn5-Directed cloning of pqq genes from Pseudomonas fluorescens CHA0: mutational inactivation of the genes results in overproduction in the antibiotic pyoluteorin. Appl. Environ. Microbiol. 61:3856-3864.
  • Schnider, U., C. Keel, C. Blumer, J. Troxler, G. Défago, and D. Haas. 1995. Amplification of the housekeeping sigma factor in Pseudomonas fluorescens CHA0 enhances antibiotic production and improves biocontrol abilities. J. Bacteriol. 177:5387-5392.
  • Sharifi-Tehrani, A., M. Zala, A. Natsch, Y. Moenne-Loccoz, and G. Defago. 1998. Biocontrol of soil-borne fungal plant diseases by 2,4-diacetylphloroglucinol-producing fluorescent pseudomonads with different restriction profiles of amplified 16S rDNA. Eur. J. Plant Pathol. 104:631-643.
  • Stutz, E. W., G. Defago, and H. Kern. 1986. Naturally occurring fluorescent pseudomonads involved in suppression of black root rot of tobacco. Phytopathology 76:181-185.
  • Whistler, C. A., N. A. Corbell, A. Sarniguet, W. Ream, and J. E. Loper. 1998. The two-component regulators GacS and GacA influence accumulation of the stationary-phase sigma factor RpoS and the stress response in Pseudomonas fluorescens Pf-5. J. Bacteriol. 180:6635-6641.
  • Whistler, C. A.; Stockwell, V. O., and Loper, J. E. 2000. Lon protease influences antibiotic production and ultraviolet tolerance of Pseudomonas fluorescens Pf-5. Appl. Environ. Microbiol 66:2718-2725.
  • Xu, G. W., and D. C. Gross. 1986 Selection of fluorescent pseudomonads antagonistic to Erwinia carotovora and suppressive of potato seed piece decay. Phytopathology 414-422.

Top of page

 

Pseudomonas fluorescens Pf-5

Comparison of Fluorescent Pseudomonas spp. Genomes

Obtaining Pf-5 Cultures

 

 

 

Link to Genome

Project Investigators

Useful Links

 

 

 

 

Contact Us

 

 

 Scientist: Joyce Loper

 

 


Last Modified: 9/30/2010
Footer Content Back to Top of Page