Mechanism of Bio-control by Fluorescent Pseudomonads

1. Fluorescent Pseudomonads:
A Brief Review on the Mechanisms of
Biological Control
Presented by
Kanishendranath Sarker
Roll. VU/ Ph.D./MCB/13 No. 10
Dept. of Microbiology
Vidyasagar University
Midnapore, West Bengal, India.
Supervisors (Joint)
Dr. Pradeep Kumar Das Mohapatra
Asst. Prof., Dept. of Microbiology, VU, Midnapore.
Dr. Subrata Dutta
Asst. Prof (Sr. Res.), Dept. Plant Pathology, BCKV, Kalyani.

2. What is Biological control?
Biological control is a bio-effector-method of controlling pests (including insects, mites,
weeds and plant diseases)using other living organisms. It relies on predation, parasitism,
herbivory, or other natural mechanisms.
Introduction to fluorescent Pseudomonads:
Pseudomonas is a genus of Gram-negative, motile, aerobic gammaproteobacteria,
belonging to the family Pseudomonadaceae containing 191 validly described species.
The members of the genus demonstrate a great deal of metabolic diversity, and
consequently are able to colonize a wide range of niches.
Some species are able to fluoresce under U.V. at 365nm.
Scientific classification (Migula, 1894)
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pseudomonadales
Family: Pseudomonadaceae
Genus: Pseudomonas

3. Fluorescent pseudomonads as biological control agent:
Since the mid-1980s, certain members of the Pseudomonas genus have been applied to
cereal seeds or applied directly to soils as a way of preventing the growth crop pathogens.
The bio-control properties of several Pseudomonas type strains are currently best
understood, although the exact mechanism of bio-control is slowly being revealed.
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
Examples of some well-known strains of fluorescent pseudomonads as bio-control agent

4. Fluorescent
Pseudomonads
Phytopathogenic
cytochrome c
oxidase-positive species
P. Cichorii
P. marginalis
P. tolaasii
Non-phytopathogenic,
nonnecrogenic
Phytopathogenic
necrogenic fluorescent
Pseudomonas spp.
without cytochrome c
oxidase
P. syringae
P. viridiflava
Taxonomic Status of Fluorescent pseudomonads (proposed by Jonhson and
Palleroni, 1989)
Continued…

5. Non-
phytopathogenic,
nonnecrogenic
strains
P. putida
Biotype A/
Biovar A
Biotype B/
Biovar B
P. Chlororaphis
P. fluorescens
Biotype A/
Biovar I
Biotype B/
Biovar II
Biotype C/
Biovar III
Biotype D/
Biovar IV; P.
chlororophis
Biotype E; P.
aureofaciens
Biotype F/
Biovar V
P. aerugenosa
…continued

6. Steps involved in Biological control
Step 1.
• Recognition by flagellin and LPS
Step 2.
• Stimulation of host defenses and
root colonization
Step 3.
• Biological control

7. Mechanisms
of biological
control
Induction of
systemic
resistance
Production of
secondary
metabolites
DAPG Pyoluteorin Pyrrolnitrin Phenazines
Competition
for iron
Pyovirdin Pyochelin
Basic mechanisms involved in biological control

8. SIDEROPHORE PRODUCTION: The
competition for Iron

9. Pyovirdin:
Pyoverdin are extracellular diffusible pigment with high affinity for Fe3+ ions. (Meyer
and Abdallah, 1978).
The hypothesis postulates that PGPR exert their plant growth-promotion activity by
depriving pathogens of iron.
under greenhouse conditions, Pseudomonas putida strain B10 suppressed Fusarium
wilt and take-all, but this suppression was lost when the soil was amended with iron
(Kloepper et. al., 1980).
in some plant–pathogen systems, Pvd-negative (Pvd–) mutants of fluorescent
pseudomonads protect plants less effectively than do the parental strains (Keel et. al.,
1989; Loper and Buyer, 1991).
Pyochelin:
Pyochelin is a relatively weak Fe3+ chelator, but a good Cu2+ and Zn2+ chelator (Cuppels
et. al., 1987; Visca et. al., 1992)
it might be able to deprive some fungi of copper and/or zinc
Siderophores are primary metabolites(because iron is an essential element), on occasion
they also behave as antibiotics.

10. Biological control exerted by Production of
SECONDARY METABOLITES

11. Production of antibiotics in several strains of fluorescent pseudomonads has been
recognized as a major factor in suppression of root pathogens
The antibiotics pyoluteorin (Plt), pyrrolnitrin (Prn), phenazine-1-carboxylic acid (PCA)
and 2,4-di-acetylphloroglucinol (Phl) have drawn great attention of research in biological
control, since they help in competition within the rhizosphere milieu (Gaur, 2002)

12. Rosales et. al., 1995
Kirner et. al., 1998
Kraus et. al., 1995
Mavrodi et. al., 1998
References
Reports of antibiotics from different producer strains involved in suppression of various
phyto-pathogens in field conditions

13. The OPERON SYSTEM of different important
antibiotics

14. The Operon systems of major antibiotics from fluorescent pseudomonads

15. Phl F, a repressor
molecule, regulates
phl operon
Produces red pigment,
helps transport of Phl
out of the cell
NOT KNOWN
cell density-dependent
Regulatory factors
Structural
gene products
stabilization of PCA-
synthesizing
multienzyme complex
PCA to
2-OH-PCA
NOT
KNOWN
Physical map of Phenazine operon (Delany et. al., 2001).
Physical map of DAPG operon(Delany et. al., 2000)

16. Structural genes
type 1 polyketide synthetase thio esterasehalogenasehalogenasehalogenase
transcriptional activator
Physical map of Pyoluteorin operon (Kirner et. al., 1998)

17. TRANSCRIPTIONAL REGULATORY MECHANISMS
of synthesis of different important
Secondary Metabolites

18. Regulation via GacS/ GacA signal transduction pathway (Haas and Défago, 2005)

19. phzI phzR phzFABCD
AHL
o
PRNAPol
o
o
PhzI PhzR
o
o o
oo
AHL-mediated Regulation

20. INDUCTION OF SYSTEMIC RESISTANCE:
The host Immunization

21. Meziane et. al., 2005
Leeman et. al., 1995
Meziane et. al., 2005
Ongena et. al., 2005
Maurhofer et. al., 1994
De Meyer et. al., 1999
Audenaert et. al., 2002
Leeman et. al., 1996
Weller et. al., 2004
References
Reports of some Bacterial traits that induce systemic resistance in host

22. Schematic model of the pathogen induced SAR and fluorescent pseudomonads
induced ISR signal transduction pathways in Arabidopsis (Pieterse et al. 2003)

23. Concluding Remarks
Despite a century long history of rhizosphere research we are still at the beginning of
understanding the complex plant-microbe interactions in this dynamic environment
In a few years, modern technologies, such as immunofluorescence microscopy, confocal
laser scanning microscopy and reporter genes, have improved the study of Pseudomonas
inoculants in soil and have markedly enhanced the knowledge about their behavior in this
environment.
Continuous searching for new approaches to improve the field efficiency and
delivery system of fluorescent pseudomonads as BCAs are strongly required to enable
sensible applications to control diseases in a sustainable manner.

24. THANK YOU
…for listening to the Endeavor