unité de bioindustries passage des déportés, 2 - 5030 ... · centre wallon de biologie...
TRANSCRIPT
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CCentre entre WWallon de allon de BBiologieiologie IIndustrielle ndustrielle (CWBI) fond(CWBI) fondéé en 1988en 1988
Université de Liège – Gembloux Agro-Bio Tech
Unité de BioindustriesPassage des Déportés, 2 - 5030 Gembloux – Belgique. Tél+32(0)81 62 2305 (Fax 6142) - www.fsagx.ac.be
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De la cellule au produit finiDe la cellule au produit fini
sélection de lasouche
étude de la physiologiemicrobienne
réacteurs
. ... .
. .
.
.
..
technologie de lafermentation
récupération etconditionnement
des cellules ou desmétabolites
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3
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4
Fermenteur 2m3
Fermentation
fermenteurs de 2 litres, 20 litres, 250 litres, 500 litres et 2 m3
MatMatéériel disponible au CWBIriel disponible au CWBI
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5
Centrifugeuses
Downstream process
centrifugeuse stérilisable, appareil d’ultrafiltation, filtre à plaque, filtre-presse, évaporateur sous vide
Evaporateur sous vide
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6
atomiseurs
Conditionnement
Sphéroniseur et extrudeur, mélangeur, atomiseurs, lyophilisateurs, lit fluidisé
lyophilisateur
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Université de Liège – Gembloux Agro-Bio Tech – Unité de BioindustriesPassage des Déportés, 2 - 5030 Gembloux – Belgique. Tél+32(0)81 62 2305 (Fax 6142) - www.fsagx.ac.be
Marc [email protected]
Embrapa, September 10, 2010
Molecular basis of biocontrol by Bacillus sp.: Lipopeptides playing in the game
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Part I:
Biopesticides, Bacillus and lipopeptides
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Why developing (microbial) biopesticides?
• Crop Quality and Yield• protective effect against diseases• Labor and Harvest Flexibility• IPM Compatibility• Resistance Management• Environmental Safety• Residue Management
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•Global pesticide market approx. $41 billion (2009)
•Biopesticides market $ 1.6 billion (2009) 15.6% annual growth rate (predicted!)
•Microbial products represent about 30 % of total biopesticide sales
Microbes as biopesticides
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Most of the bacterial strains exploited as biopesticides belong to the genera:
Streptomyces, Agrobacterium, Bacillus and Pseudomonas
Bacillus‐based products represent about half of the commercially available bacterial biocontrol agents
(B. subtilis, B. amyloliquefaciens, B. licheniformis, B. pumilus...)
Bacteria as biopesticides
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Why is Bacillus among the best candidates for developing biopesticides?
Multifactorial basis!
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Efficient producer of antibiotics (more than two dozen)
> antibiosis towards phytopathogens
Efficient colonizer of root systems (soil bacterium)
> compet. for space and nutrients – growth promotion
Bacillus sp. as biopesticide
‐ Controls + Feng
Botrytis‐infected apples
Bs C
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Efficient spore former
> persistence ‐ formulation
Bacillus sp. as biopesticide
Efficient enhancer of plant resistance
> Strenghthening of the host
C LP
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Beneficial effects of B. amyloliquefaciens strain S499 on tomato in Burundi
Bacillus sp. as biopesticide
And efficient in the field…
Multiple examples of disease control in the litterature
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High level of protection (75%) against the disease caused by the endemic Fusarium pathogen
0
1
2
3
4
5
6
7
C 10exp5 10exp6 10exp7 10exp8
Mean diam
eter of n
ecrosis (cm
)
Bacterial inoculum concentration (CFU/ml)
a b c A
B
Bacillus sp. as biopesticide
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Growth promotion
Increased fruit yield
Bacillus sp. as biopesticide
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What are lipopeptides and why are they interesting?
Biosurfactant… with multiple functions!
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LPs from plant‐associated bacteria: a panoply of structures
Pseudomonas, Bacillus, Serratia
Families ‐ Variants ‐ Homologues
Synthesized via NRPS
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Surfactins
Heptapeptides cyclic lactone ring
4 structural variantsVarious homologues C12 to C15, linear, iso, anteiso
Iturins
heptapeptides linked to a b‐amino fatty acid
7 structural variants(Bacillomycins, mycosubtilins, iturins A)Homologues C14 to C17
4 structural variantsHomologues from C14 to C18
Fengycins
Lipodecapeptides, internal lactone ring
Bacillus lipopeptides
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Colonization, biofilm
Antiviral
Antiprotozoal
Antibacterial
Antioomycete Antifungal
Chelation,solubilization
Motility Virulence,Immunization
Natural functions of LPs
Raaijmakers et al. 2010
involved in biocontrol
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Beneficialrhizobacteria
Involvement of surfactins in pellicle/biofilm formation and motility (Hofemeister et al. 2004 Mol. Genet. Genomics; Branda et al. 2001 Proc. Natl. Acad. Sci. U. S. A.)
Role of surfactin in biofilm formation by B. subtilis on Arabidopsis roots (Bais et al. 2004 Plant Physiol.)
FZB42 wtSrf+Fen+
Bac+
AK3 deriv Srf+Fen-
Bac-
CH1 deriv Srf-Fen+
Bac-
CH2 derivSrf-Fen-
Bac+
Involvement in root colonization
Role of massetolide in colonization of tomato roots (Tran et al. 2007 New Phytol.)
‐ Spreading (reduce surface tension, wettability agents)‐ Attachement (hydrophobic surfaces, plant tissues)‐ Biofilm developement
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Pathogen
Involvement in direct antagonism
- LP + LP
Bacterial cell/fungal spore lysis, inhibition of hyphal developement
Soil‐borne diseases: iturins involved in the control of R. solani (Asaka, Shoda 1996 Appl Environ Microbiol) and P. aphanidermatum on tomato (Leclère et al. 2005 Appl. Environ. Microbiol.)
Phyllosphere diseases: surfactins for reduction of the infection caused by P. syringae on Arabidopsis. Iturins and fengycins in the antagonism toward Podosphaera fuscainfecting melon leaves
Post harvest diseases: fengycins in gray mold disease (Botrytis cinerea) reduction on apple fruits (Ongena et al. 2005 Appl. Microbiol. Biotechnol.)
Detergent, pore forming activity
- LP + LP
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Pathogenrestriction
Host plant immunization
C LP
Involvement of LPs in ISR elicitation
● Disease reduction on leaves upon root treatment with purified LPs
● Disease reduction on leaves upon root treatment with mutants
● No migration of inducing agent from roots to the infected leaves
● Efficient production of the inducing agent in the rhizosphere
● Protection associated with defence responses at the molecular level
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Specific biocontrol‐related activities for the three Bacillus LP families
powerful biosurfactants
Antiviral
Antibacterial
low fungitoxicity
Strongly antifungal (yeast and fungi)
low antibacterial
no antiviral activities
Surfactins Iturins
strongly fungitoxic (filamentous fungi )
Fengycins
Root colonization (biofilm formation, surface motility)
Direct antagonism toward phytopathogens
Involvement in plant systemic resistance elicitation
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Still a very small part of the global market for Bacillus-based biocontrol products…
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Why are microbial biopesticides not so successful ?
Limitations in efficacy – Inconsistency !
Need for a better understanding of what happens in the phytosphere regarding secretion of bioactive compounds
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‐ Auxiliary microflora‐ Root zone‐ Soil type, heterogeneity‐ pH, T, pO2
‐ Plant species, cultivar, developmental stage
Selection of specific microbial populations by the plant through :
‐ Release of soluble carbon compounds and other rhizodeposition‐ pH and redox‐modulating factors‐ Release of complexing agents (siderophores, phenols, carboxylates)‐ Release of antimicrobials (antibiotics, quorum sensing inhibitors)‐ Exudation of specific stimulatory compounds‐ Shaping specific habitat conditions
Rhizosphere factors influencing microbes
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Are LPs actually secreted upon growth of Bacillus on plant roots?
What’s the influence of rhizosphere‐specific parameters on LP production rate?
Is the LP signature influenced by the host plant species ?
Not only microbial communities but also expression of biocontrol traits may be influenced by the host plant type and environmental factors
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Part II:
In situ production of Bacillus lipopeptides
1. LP production on various host plants
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B. subtilis S499: a natural strain
Efficient producer of the three LP families srf, fen and itu
recalcitrant to transformation
Determination of the LP pattern produced in the rhizospheres(quantitative, qualitative)
Differential expression of srf, fen and myc genes
Development of extract./LC‐DAD‐ESI‐MS methods
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LP production in the rhizosphere of hydroponic plants (non sterile)
LC‐MSExtraction
Populations on most plants > 105 cfu/g root FW but estimated
The three LP families are differentially produced in the rhizosphere
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LP production in the rhizosphere of in vitro‐grown plants (sterile)
Colonization (cfu/g root FW, 2 weeks p.i.)
corn lettuce bean tomato cucumber soy
2,6. 106 2,8. 107 1,8. 107 2,3. 107 nd nd
Imaging TOF‐MS
Transfer on silicium plate
LP analysis
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Control
Bacillus‐colonized root
Srf
Itu
Fen
Inner MS cameraScanned zone
Fingerprint on silicium plate
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Srf
Itu
Fen
Larger root section
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LP production in exudates
Exudates collected from hydroponic and non‐treated plants (4 weeks)
Root exudates seem to be more conducive for itu and srf synthesis
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srf
itu
fen
LP production in individual C sources
Liquid cultures to test substrates individually
Exudates recomposed on the basis of substrates typically found in tomato as described by Kamilova et al., 2006
Higher srf production in the presence of organic acids
C14 and C15 are the forms mainly produced also in the presence of root exsudates
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cLPs synthesis also influenced qualitatively…
Long chain homologues seem to be favored
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Generally:
LP signature may be strongly influenced by the host plant species
‐> Better to use of the Bacillus strain for biocontrol on some specific crops?
In summary…
Quantitatively:
In half of the plants tested so far, srf is seemingly the main LP secreted by S499
Fen are very poorly detected in the rhizosphere. Does it reflect reality?
300 ng/g root FW corresponds to ~ 0.12 µM in the hydroponic medium. Is it sufficient? LPs are active at 5‐30 µM concentrations
Qualitatively:
Long chain homologues seem to be favored (tomato and corn)In some instances, long chain LP homologues demonstrated to be more active
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2. More insights about surfactin synthesis in the rhizosphere
Part II:
In situ production of Bacillus lipopeptides
1. LP production on various host plants
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Combination of two approaches:
Ex vivo: batch cultures, bioreactor/chemostat
In vivo: mass spectrometry, reporter genes lacZ
BGS3 derivative < BC25: lacZ reporter system under the control of the psrf gene
thrCpsrf
lacZ thrC
B. subtilis BGS3: a « laboratory » strain
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Expression of srfA genes in the rhizosphere
Higher surfactin gene expression during the period where BGS3 cells maintain a stable population
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Confirmation of relatively high srfA expression at low growth rate
Influence of µ tested in chemostat cultures
Growth rate
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Surfactin production in the rhizosphere
Collection of roots and nutrient solution
C18 extract. of NS
MeOH/Triton extract of root surface
C18 extract.
320 ± 80 µg surfactin / 108 cells= approx. 1.8 µM in the plant growthmedium
LC-MS
+
Surfactin recovery from the rhizosphere in the range of concentrations necessary for triggering plant resistance or defense reactions (2-5 µM)
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Gene expression Surfactin productionβ‐gal U µg/108 cells
Optimized medium 53 ± 11 470 ± 35
Natural exudates 17 ± 3 140 ± 40
Recomposed exudates 25 ± 1.7 340 ± 75
srfA gene expression and lipopeptide secretion into the medium also effective upon growth of BGS3 in tomato root exudates
Surfactin synthesis in root exsudates
Exudates collected from non‐bacterized tomato plantlets after 23‐25 days of growth in nutrient solution under sterile conditions (suppl. (NH4)2SO4 )
Exudates recomposed on the basis of substrates typically found in tomato exudates as described by Kamilova et al., 2006
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Liquid cultures to test substrates individually (flasks)
Effect of carbon sources on surfactin synthesis
Biomass production
Higher cell concentration in sugars and a.a. but efficient growth on most substrates except Ara
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srfA gene expression
Effect of carbon sources on surfactin synthesis
Market effect of Ara ?Higher expression in the presence of a.a. and some organic acids
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Surfactin production
Higher production in organic and amino acids
C14 and C15 mainly produced are also the more active forms
Effect of carbon sources on surfactin synthesis
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No significant effect of cell immobilization/development on solid support/roots
Similar trends in surfactin gene expression and production on gelified media
Other clues…
Higher surfactin production in the presence of Fum, Mal, Cit, Asp, Glu
Higher gene expression in the presence of organic acids and a.a.
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Culture conditionsBiomass
(cells x 108/ml)
srfA expression
(b‐gal /108 cells)
Surfactin prod.
(mg/108 cells)
Bioreactor, 1 vvm, 300 rpm 6.1 54 550
Aerated flask 5.6±0.3 47±11 660±70
Sealed flask + nitrogen flushed 3.3±0.7 18±4 480±40
Limited effect of low aeration rate on surfactin synthesis
Other clues…
Low oxygen availability in soil not detrimental to surfactin production
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Other clues…
Effect of Temperature
Effect of pH
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Rhizosphere conditions conducive to surfactin secretion by B. subtilis with regards to: ‐ exudates
‐ growth rate‐microcolonies‐ oxygen status
In summary…
The surfactin pattern may also be influenced by‐ the nutritional basis imposed by the host plant‐ the immobilization (not shown)‐ oxygen availability (not shown)
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Need for a better understanding of the mode of action of the bioactive compounds
Why are microbial biopesticides not so successful ?
Limitations in efficacy – Inconsistency !
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Part III:
Bacillus lipopeptides as elicitors of resistance in the host plant
1. Demonstration for a role of LP in triggering systemic resistance
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Primed state
Pathogen
Infection
Colonization
PGPR
Induced resistance state
Pathogen restriction
Rhizobacteria‐induced systemic resistance (ISR) in plants
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Disease reduction on leaves upon root treatment with purified LPs
Demonstration of LP involvement in ISR stimulation
ISR activitytomato bean cucumber tobacco
B. subtilis strain S499 ++* ++* ++* ++* Surfactin (5‐10 µM) ++* ++* ‐ ++
P. fluorescens SS10 ++* n.t. n.t. n.t.Massetolide (22‐44 μM) +* n.t. n.t. n.t.
++, 25‐40% disease reduction*, statistically different from disease controln.t., not tested
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Disease reduction on leaves upon root treatment with mutants
Demonstration of LP involvement in ISR stimulation
ISR activitytomato bean cucumber tobacco
B. subtilis wt 168 ‐ ‐ n.t. n.t.Surfactin overproducer ++* ++* n.t. n.t.
P. fluorescens SS10 ++* n.t. n.t. n.t.Massetolide suppressed ‐ n.t. n.t. n.t.
++, 25‐40% disease reduction*, statistically different from disease controln.t., not tested
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No migration of inducing agent from roots to the infected leaves
Demonstration of LP involvement in ISR stimulation
OK
Production of the inducing agent in the rhizosphere
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Macroscopic protection associated with defence responses at the molecular level
Demonstration of LP involvement in ISR stimulation
Stimulation of early defence events (oxidative burst) in roots of plants treated with surfactin
Srf
Ctrl
Time in min
0 30LOCAL
Not the « SAR‐type » ISR
SIGNALLING1 2 3
1: BTH treated plants; lanes 2: control plants; 3: Bac. S499‐treated plants
> No (free) SA accumulation and no PR protein expression in plants induced by surfactin producers
> ISR induced by massetolide also in nahG tomato plants no longer able to accumulate SA
PR1
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Nucleus
H2O2NADPH oxydase
2 O2 2 O2.-
2 NADPH2 NADP + 2 H+
SOD
H2O2
H+
ATP ADP+Pi
NO3-
Cl-K+
H+
Ion fluxespH
Ca2+
Unsaturated fatty acids
Kinases Defense gene activation
PL A2PL C
PALLOX
Phenoliccompounds
Octadecanoidpathway
?
Oxidative burst
EARLY EVENTS INDUCED IN TOBACCO CELLS
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Macroscopic protection associated with defence responses at the molecular level
Demonstration of LP involvement in ISR stimulation
Stimulation of key enzyme activities (LOX, LHP) of the oxylipin pathway within 48 h.p.i. (new LOX gene isoform) in leaf tissues
possible accumulation of antifungal volatiles and/or signalling compounds (JA)
0 48 96 0 48 96 MeJA
Control Bs2500
Lox F
C C CBs Bs Bs0 48 96 hpi
> Accumulation of antifungal compounds (phytoalexins) in leaves of plants treated with surfactin overproducer isolate
SYSTEMIC
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Surfactins stimulate ISR in various plants, fengycins are also active albeit to a lower extent, but iturins are not
Fengycins and surfactins (less active) induce phenolic accumulation in potato tuber cells but iturin do not.
In tobacco cells, surfactins trigger a whole set of defence‐related early events while fengycins only stimulate later enzyme activities and iturins are not active.
Differential activity of LP families on plants
From Bacillus:
Surf
Itu
Feng
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2. How do LPs work at eliciting plant cells?
Part III:
Bacillus lipopeptides as elicitors of resistance in the host plant
1. Demonstration for a role of LPs in triggering systemic resistance
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More insights into the molecular interaction of cLPs with plant cells
elicitorsreceptors bilayer perturbation?
Elicitor perception
Rhizobacteria
Early events
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FlagellaLipopolysaccharidesBiosurfactants
lipopeptidesrhamnolipids
N‐acyl‐L‐homoserine lactoneN‐alkylated benzylamineSiderophores
1. Pseudobactins SA and SA‐containing siderophores.
Antibiotics1. 2,4‐Diacetylphloroglucinol2. Pyocyanin
VolatilesExopolysaccharides
ISR elicitors from rhizobacteria
Receptor (also PAMP)Low‐affinity receptor (also PAMP)??
?????? (iron stress)
??
????
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Defense‐related events stimulated by LPs in cultured plant cells (Tobacco)
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Nucleus
H2O2NADPH oxydase
2 O2 2 O2.-
2 NADPH2 NADP + 2 H+
SOD
H2O2
H+
ATP ADP+Pi
NO3-
Cl-K+
H+
Ion fluxespH
Ca2+
Unsaturated fatty acids
Kinases Defense gene activation
PL A2PL C
PALLOX
Phenoliccompounds
Octadecanoidpathway
?
Oxidative burst
Early and later defense events elicited by surfactin in plant cells
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Differential activities of the 3 families (fengycin only induce later
response, iturin not active)
> role of structural features in the peptide?
Similarities with the early responses to PAMPs
Mechanism of surfactin perception
Strong interaction with lipid bilayers in model systems
Biocidal activity relying on pore formation within the envelop of the target (virus, bacteria)
Specific receptors? Interaction with plasma membrane ?
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0
20
40
60
80
100
120
140
160
180
200
Mix C12 C13 C14 ni C14 nn C14 ni,m C14 ni,l C14 ni,lm C15
Activity (%
)
0
20
40
60
80
100
120
140
160
180
200
Mix C12 C13 C13 Val7 C13 Leu4 C14 C14 Leu4 C14 Ile C15 C15 Val7 C15 Leu4 C15 Ile
Activity (%
)
■ Structure/activity: comparison of multiple homologues and variants
Specific aspects in the interaction between surfactin and plant cells
Chemical synthesis Metabolic engineering
LinearizedMethylated
Natural co-production
C12, C13, C14i+n, C15 Amino-acid substitutions(Leu<>Val<>Ile)
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■ Structure/activity: the more lipophilic the more active, crucial role for the amphiphilic character, the neo‐synthesized peptide forms are the more active
Specific aspects in the interaction between surfactin and plant cells
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■ Structure/activity: no crucial role for a.a. sequence, the more lipophilic the more active, crucial role for the amphiphilic character
■ No competitive effect between homologues
Specific aspects in the interaction between surfactin and plant cells
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■ Structure/activity: no crucial role for a.a. sequence, the more lipophilic the more active, crucial role for the amphiphilic character
■ No competitive effect between homologues
0
0,2
0,4
0,6
0,8
1
1,2
0 2 4 6 8 10 12 14 16 18 20
ΔpH
Surfactin concentration (µM)
C
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20
Rel
ativ
e H
202
accu
mul
atio
n
Surfactin concentration (µM)
B
■Micromolar concentrations required (EC50 ~ 2.5 µM) for activity
Specific aspects in the interaction between surfactin and plant cells
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■ Structure/activity: no crucial role for a.a. sequence, the more lipophilic the more active, crucial role for the amphiphilic character
■ No competitive effect between homologues
■Micromolar concentrations required (EC50 ~ 2.5 µM) for activity
■ No secondary oxidative burst associated with HR and very limited cell death
Specific aspects in the interaction between surfactin and plant cells
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■ Structure/activity: no crucial role for a.a. sequence, the more lipophilic the more active, crucial role for the amphiphilic character
■ No competitive effect between homologues
■Micromolar concentrations required (EC50 ~ 2.5 µM) for activity
■ No secondary oxidative burst associated with HR and very limited cell death
■ No refractory state phenomenon
S C14, 10 µMS C14, 10 µM
Specific aspects in the interaction between surfactin and plant cells
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Specific aspects in the interaction between surfactin and plant cells
■ Structure/activity: no crucial role for a.a. sequence, the more lipophilic the more active, crucial role for the amphiphilic character
■ No competitive effect between homologues
■Micromolar concentrations required (EC50 ~ 2.5 µM) for activity
■ No secondary oxidative burst associated with HR and very limited cell death
■ No refractory state phenomenon
> Talk against the presence of a high affinity/receptor‐based surfactin recognition system in plants
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■ Surfactin fully insert into plasma membrane fraction
Specific aspects in the interaction between surfactin and plant cells
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■ Surfactin fully insert into plasma membrane fraction
■ Higher affinity for membrane of long‐ chain surfactins, significant decrease in affinity for methylated and/or linear surfactins
Specific aspects in the interaction between surfactin and plant cells
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■ Surfactin fully insert into plasma membrane fraction
■ Higher insertion rate in membrane for long‐ chain surfactins, significant decrease for methylated and/or linear surfactins
■ No significant change in insertion rate of C14 surfactins in heat‐treated or protease‐treated cells/protoplasts (not shown)
Specific aspects in the interaction between surfactin and plant cells
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■ Surfactin fully insert into plasma membrane fraction
■ Higher insertion rate in membrane for long‐ chain surfactins, significant decrease for methylated and/or linear surfactins
■ No significant change in insertion rate of C14 surfactins in heat‐treated or protease‐treated cells/protoplasts (not shown)
■ Data from Iso Thermal Calorimetry using model vesicles
Specific aspects in the interaction between surfactin and plant cells
Surfactin activity on eucaryotic cells:not or poorly active on fungi> 15 µM (not toxic) on mammalian cells, within hours> 2.5 µM (not toxic) on tobacco cells, within minutes
Affinity related to phospholipid and/or sterol content of plasma membrane?
> Specific targetting in rafts?
Martin et al. (2005) Trends Plant Sci.
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Surfactin interacts spontaneously with model vesicles, in an endothermic and entropy‐driven process > Confirm strong hydrophobic and dose‐dependent interactions (no signal < 2µM, similar as biological activity on tobacco cells)
Lipid composition of vesicles K (mM‐1)POPC 1mM 39,5±4,1PLPC 1mM 43,1±1,3PLPC/Stigmasterol 9/1 1mM 39,2±3,8PLPC/Stigmasterol 3/1 1mM 27,4±3,4PLPC/Ergosterol 3/1 1mM * 34,0±0,8DPPC/PLPC 3/1 1mM 61,1±5,3DPPC/POPC 3/1 1mM * 85,4±8,5* Result from one measurement
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Strong difference in partitioning constants between C13 and 14 homologues as well as between surfactin and fengycins and iturins which interacted spontaneously (ΔG<0) but in an exothermic manner with vesicles by contrary to surfactins
Lipid composition of vesicles K (mM-1)Surfactin C13 8,3Surfactin C14 30,9Surfactins mix 54Fengycins 9,4Iturins 31,8
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Close relationship between the physical structure of the lipid bilayer and the association of surfactin with the bilayer
Lipid composition of vesicles Lipid phases KPOPC/PSM 0.1/0.9 GelPOPC LdPOPC/Chol 0.45/0.55 Lo POPC/PSM/Chol 0.5/0.25/0.25 Ld + Lo (raft)POPC/PSM/Chol 0.2/0.5/0.3 Lo + GelPOPC /PSM 0.6/0.4 Ld + GelPOPC/PSM/Chol 0.4/0.5/0.1 Ld + Lo + Gel
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■ Surfactin fully insert into plasma membrane fraction
■ Higher insertion rate in membrane for long‐ chain surfactins, significant decrease for methylated and/or linear surfactins
■ No significant change in insertion rate of C14 surfactins in heat‐treated or protease‐treated cells/protoplasts (not shown)
■ Data from Iso Thermal Calorimetry using model vesicles
Specific aspects in the interaction between surfactin and plant cells
Talk in favor of a role as “sensor”of the plasma membrane with surfactin‐induced disturbance or rearrangement, lauching defense signalling cascade
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Favour the ecological fitness of the producing isolates in the phytosphere:
> Niche colonization (motility, biofilm)> Competitive interactions with the other organisms
More than just antibiotics!
> Immuno‐stimulation in plants
May impact on various cell processes without causingany detrimental leakage in membrane
‐ Cytotoxicity /antagonism‐ Inhibition of pathogen attachement/biofilm ‐ Interference with fungal toxin synthesis (fumonisin, aflatoxin)‐ Signalling in molecular dialogue with predators
Molecular pneumatic drills
and
In conclusion
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What factors drive the perception at the membrane level?
Cannot conclusively rule out the involvement of low‐affinity proteic receptors
‐ Testing other structural variants on tobacco cells and in ITC‐ Testing reactivity of cells from other plants with different phospholipids‐ Testing binding of radiolabelled surfactin on proteic fraction of plant membrane
Surfactin among the rare Bacillusmetabolites identified so far as plant immuno‐stimulators (2,3‐butandiol)
Shen et al. 2009
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Competitive advantage of an efficient production of surfactin, fengycin and iturin with specific roles and targets (synergistic effects)
May explain why some Bacillus or Pseudomonas strains are efficient and others not
Rapid method of screening for the selection of useful strains that co‐produce the broadest panoply of LP families should display a multi‐faceted biological control
In the context of biocontrol
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Thank you…
Financial support from FRS‐F.N.R.S, F.R.I.A. and Walloon Region in Belgium.
For more information:
Ongena et al. 2007 Environ. Microbiol. 9, 1084Adam 2008 PhD thesis, Univ. LiègeAdam et al. 2008 BMC Plant Biol. 8, 113Jourdan et al. 2009 Mol. Plant Microbe Interact. 22, 456Nihorimbere et al. 2009 Environ. Microbiol. Rep. 1, 124