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Pierson Lab

Pierson Lab. The Pseudomonads in Biological Control. Microbial gene regulation. Root-associated free-living bacteria. Microbial community interactions. Plant disease control. Importance of plant diseases. Estimated annual crop production worldwide . $1.2 - 1.3 trillion.

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Pierson Lab

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  1. Pierson Lab The Pseudomonads in Biological Control Microbial gene regulation Root-associated free-living bacteria Microbial community interactions Plant disease control

  2. Importance of plant diseases Estimated annual crop production worldwide $1.2 - 1.3 trillion Amount lost to disease, insects, weeds using current control measures $500 billion Additional losses without current control measures $330 billion Apple scab Fireblight of pear Take-all of wheat Citrus canker Verticillium wilt

  3. What determines disease? Species Plant Genotype Stage of growth Stress Pathogen Environment Genotype: hrp, avr race Humidity Dispersal, colonization site H2O Plant factors Other Microbes

  4. Current approaches to disease control Chemical Breeding 1995: United States spent $26 billion on chemical pesticides Identification of resistance genes Introgressing into commercial cultivars Of this, < 1% actually gets to where the pathogen is What happens to the rest? Problems with development of resistance, pyramiding genes Ground water Taken up by the plant Development of resistance Biological Control is an attractive alternative/supplement

  5. Nutrient Competition Site Competition Antibiosis Cross-communication How does Biological Control by Pseudomonads work? Biological Control

  6. The Rhizosphere The zone of soil influenced by the plant root Plants can exude ca. 70% of fixed carbon through their roots Rhizosphere is a dynamic environment

  7. The rhizosphere comprises  50% of the biomass of the plant (From Kutschera, L & Lichtenegger, E. 1992 Wurzelatlas Mitteleuropaischer Grundpflanzen Gustav Fischer Verlag Stuttgart) “There is more biomass below the earth’s surface than above it.”

  8. Examples of Biological Control Pseudomonads Take-all of wheat (Gaeumannomyces graminis var. tritici) Pseudomonas aureofaciens 30-84 Pseudomonas fluorescens Tx-1 Dollar spot of turf (Sclerotinia homoeocarpa) Pseudomonas fluorescens Pf-5 Damping off of bean (Rhizoctonia solani) Drechslera leaf spot (D. poae) Pseudomonas fluorescens F113 Damping off of bean (Pythium ultimum) Damping off of bean (Pythium ultimum) Pseudomonas aureofaciens AB254 Pseudomonas fluorescens WCS365 Rhizoctonia solani Pseudomonas fluorescens A506 Fireblight of pear (Erwinia amylovora) Pseudomonas putida Phytophthora root rot of citrus Canadian thistle Pseudomonas syringae pv. tagetis

  9. Nutrient Competition Mechanisms of Biological Control by Fluorescent Pseudomonads Biological Control

  10. Control of Rhizoctonia solani on cotton by P. cepacia D1 Rhizoctonia solani Produces fluorescent siderophores Chelates Fe in environment All organisms require Fe Fe available at 10-18 M

  11. P. cepacia D1 Control Cotton R. solani

  12. Take-all Disease of Wheat No. 1 disease of cereals worldwide (up to 50% yield loss) One infected root in 10,000 is sufficient to cause an epidemic Caused by Gaeumannomyces graminis var. tritici (Ggt) No varieties of wheat or barley exist with specific resistance to take-all. No direct method of chemical control is presently available.

  13. Take-all disease of wheat Pathogen: Gaeumannomyces graminis var. tritici Invades root vascular tissues Physically blocks water & nutrient transport

  14. Take-all Decline- An Example of Natural Suppression Suppressive Conducive Pseudomonas aureofaciens 30-84 Take-all Disease Years of wheat monoculture

  15. Antibiosis Mechanisms of Biological Control by Fluorescent Pseudomonads Biological Control

  16. Pseudomonas aureofaciens Produces Phenazine Antibiotics N COOH N COOH N OH OH N N N 2-OH-PZ 2-OH-PCA PCA “Phenazine Phacts” Broad spectrum Block respiration Pathogen inhibition Competitive fitness

  17. 30-84.44-8 (Phz-) 30-84 Phenazines required for pathogen inhibition Restored Phz- 30-84 30-84 Phz- Restored Ggt

  18. o o o o o o o P RNAPol AHL-mediated Gene Regulation AHL acyl-ACP + o ADO-Met PhzI PhzR phzFABCD phzI phzR

  19. o o o o o o Cell Surface csaI csaR o o o o o o o o o o o o o o o o o Biofilms RpeA (+) Exoprotease rpeA PhzI PhzR CsaR CsaI (+) (+) (+) phzI phzR phzXYFABCD (+) (+) GacA RpoS (+) GacS

  20. AHL Regulatory System P P phzI phzR phzI P phzR 30-84 (PhzR++) 30-84 30-84R (PhzR-) 30-84R (PhzR-) 30-84Z (Phz-, AHL+) Lawn of 30-84I (PhzI-) phzB phzF phzA phzC phzD

  21. O O N O H OH O H O N H O O O O N O H O O O O O N H O O O O N H O O Butyryl HSL P. aeruginosa Hydroxybutyryl HSL V. harveyi 3-oxohexanoyl HSL V. fischeri O O Hexanoyl HSL P. aureofaciens N H O O Octanoyl HSL V. fischeri N H 3-oxooctanoyl HSL A. tumefaciens 3-oxododecanoyl HSL P. aeruginosa O H OH 3R-hydroxy-7-cis-tetradecenoyl HSL R. leguminosarum O N H

  22. What’s this guy thinking? He’s Nuts!! Wanna Rumble! Let’s get together! I hear you! What about the Microbial Community?

  23. Potential Roles of Bacterial Communication • Coordinating gene expression • Competition • Survival • Pathogen inhibition • 2. Interspecies communication • Recognition and defense • Consistency of biological control • Biofilm formation & structure

  24. Negative Positive Cross-communication

  25. Cross-communication Mechanisms of Biological Control by Fluorescent Pseudomonads Biological Control

  26. Why is communication important? PU-186 Enhance pathogen inhibition... PU-186 + 30-84I 30-84I Reduce pathogen inhibition... Mixture Ave. Inhibition (mm) 30-84 8.9 ± 1.0a 0 ± 0b PU-5 0 ± 0b PU-15 30-84 + 5 2.7 ± 1.1c 30-84 + 15 1.3 ± 2.3c Alter rhizosphere competition... Determine the composition & structure of the root community... Can:

  27. Microbial Communities: Biofilms

  28. Competition Antagonism Cross-communication Conclusions Plant diseases cause major loss of food and money Biological control an attractive alternative to chemicals Many biocontrol bacteria identified are Pseudomonads Biological control occurs via several mechanisms

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