Post on 02-Feb-2016
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Pierson LabPierson Lab
Microbial gene regulationMicrobial gene regulation
Root-associated free-living bacteriaRoot-associated free-living bacteria
Microbial community Microbial community interactionsinteractions
Plant disease Plant disease controlcontrol
The Pseudomonads in Biological Control
Importance of plant diseases
Estimated annual crop production worldwide
Amount lost to disease, insects, weeds using current control measures
Additional losses without current control measures
$1.2 - 1.3 trillion$1.2 - 1.3 trillion
$500 billion$500 billion
$330 billion$330 billion
Verticillium wiltVerticillium wilt
Citrus cankerCitrus canker
Fireblight of pearFireblight of pear Apple scab
Take-all of wheatTake-all of wheat
Plant
Pathogen EnvironmentHumidityH2O
GenotypeStage of growth
Species
Stress
Genotype: hrp, avr raceDispersal, colonization site
Plant factors
Other Microbes
What determines disease?
1995: United States spent $26 billion$26 billion on chemical pesticides
Of this, < 1%< 1% actually gets to where the pathogen is
What happens to the rest?
Ground water
Taken up by the plant
Development of resistance
Current approaches to disease control
Chemical
Identification of resistance genes
Introgressing into commercial cultivars
Problems with development of resistance, pyramiding genes
Breeding
Biological Control is an attractive alternative/supplement
How does Biological Control by Pseudomonads work?
Nutrient Competition
Cross-communication
Biological ControlSite Competition Antibiosis
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
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.”
Pseudomonas fluorescens Tx-1 Dollar spot of turf (Sclerotinia homoeocarpa)
Pseudomonas aureofaciens 30-84 Take-all of wheat (Gaeumannomyces graminis var. tritici)
Pseudomonas fluorescens Pf-5 Damping off of bean (Rhizoctonia solani)
Pseudomonas fluorescens F113 Damping off of bean (Pythium ultimum)
Pseudomonas aureofaciens AB254 Damping off of bean (Pythium ultimum)
Drechslera leaf spot (D. poae)
Pseudomonas fluorescens WCS365 Rhizoctonia solani
Pseudomonas fluorescens A506 Fireblight of pear (Erwinia amylovora)
Pseudomonas putida Phytophthora root rot of citrus
Pseudomonas syringae pv. tagetis Canadian thistle
Examples of Biological Control Pseudomonads
Mechanisms of Biological Control by Fluorescent Pseudomonads
Nutrient Competition
Biological Control
Produces fluorescent siderophores
Chelates Fe in environment
Fe available at 10-18 M
All organisms require Fe
Control of Rhizoctonia solani on cotton by P. cepacia D1
Rhizoctonia solani
P. cepacia D1
R. solani
Cotton
Control
Take-all Disease of Wheat
Caused by Gaeumannomyces graminis var. tritici (Ggt)
No. 1 disease of cereals worldwide (up to 50% yield loss)
One infected root in 10,000 is sufficient to cause an epidemic
No varieties of wheat or barley exist with specific resistance to take-all.No direct method of chemical control is presently available.
Take-all disease of wheat
Pathogen: Gaeumannomyces graminis var. tritici
Invades root vascular tissues
Physically blocks water & nutrient transport
Take-all Decline- An Example of Natural Suppression
Years of wheat monoculture
Tak
e-al
l D
isea
se
SuppressiveConducive
Pseudomonas aureofaciens 30-84
Mechanisms of Biological Control by Fluorescent Pseudomonads
Biological Control Antibiosis
Pseudomonas aureofaciens Produces Phenazine Antibiotics
2-OH-PCA2-OH-PCAPCAPCA 2-OH-PZ2-OH-PZ
OHOH
NN
NN COOHCOOHCOOHCOOH
NN
NNOHOH
NN
NN
Pathogen inhibition
Competitive fitness
“Phenazine Phacts”
Broad spectrum
Block respiration
Phenazines required for pathogen inhibition
30-8430-8430-8430-84
Phz-Phz-
Phz-Phz-RestoredRestored
RestoredRestored
Ggt 30-
84.
44-8
(P
hz
30-
84.4
4-8
(P
hz-- ))
30-
84
30-
84
phzIphzI phzRphzR phzFABCD
AHL
oacyl-ACP +
ADO-Met
PRNAPolRNAPol
o
o
PhzIPhzI PhzRPhzR
AHL-mediated Gene Regulationo
o o
oo
phzXYFABCD
CsaRCsaRCsaICsaI
(+)
(+)
(+)GacAGacARpoSRpoS
csaIcsaI csaRcsaR
GacSGacS
oo
(+)
o
o o
o
o
o
o
phzI phzR
(+)(+)(+)
o
oo
PhzIPhzI PhzRPhzR
o
o
o
ExoproteaseExoprotease
o
rpeArpeA
BiofilmsBiofilmsCell SurfaceCell Surface
RpeARpeA
o
oo
o
o
oo
AHL Regulatory System
phzF phzA phzB phzC phzD
P
30-8430-8430-84R (PhzR-)30-84R (PhzR-) 30-84 (PhzR30-84 (PhzR++++))
phzRP
phzR
phzIP
phzI
Lawn of 30-84I (PhzI-)
30-84R (PhzR-)
30-84Z (Phz-, AHL+)
O
O
H
N
O
O
OH
O
H
N
OH
O
OO
H
N
O
O
OO
H
N
O
O
O
H
N
O
O
O
H
N
O
O
O
H
N
O
O
3-oxohexanoyl HSL
Hydroxybutyryl HSL
3-oxooctanoyl HSL
3-oxododecanoyl HSL
Hexanoyl HSL
Octanoyl HSL
Butyryl HSLP. aeruginosa
V. harveyi
V. fischeri
P. aureofaciens
V. fischeri
A. tumefaciens
P. aeruginosa
OHO
H
N
O
O
H3R-hydroxy-7-cis-tetradecenoyl HSL
R. leguminosarum
What about the Microbial Community?
What’s this guy thinking?
He’s Nuts!!
Let’s get together!
Wanna Rumble!
I hear you!
Potential Roles of Bacterial Communication
1. Coordinating gene expression
CompetitionSurvivalPathogen inhibition
2. Interspecies communication
Recognition and defenseConsistency of biological controlBiofilm formation & structure
Positive Negative
Cross-communication
Mechanisms of Biological Control by Fluorescent Pseudomonads
Cross-communication
Biological Control
Why is communication important?
Determine the composition & structure of the root community...
Alter rhizosphere competition...
Reduce pathogen inhibition...
30-84
30-84 + 530-84 + 15
2.7 ± 1.1c
8.9 ± 1.0a
1.3 ± 2.3c
Mixture Ave. Inhibition (mm)
PU-5
PU-15
0 ± 0b
0 ± 0b
Enhance pathogen inhibition...
PU-186
30-84I PU-186 + 30-84I
Can:
Microbial Communities: Biofilms
Conclusions
Biological control an attractive alternative to chemicals
Many biocontrol bacteria identified are Pseudomonads
Plant diseases cause major loss of food and money
Biological control occurs via several mechanisms
Competition
AntagonismCross-communication