biological control mechanism- by kanish
TRANSCRIPT
Fluorescent Pseudomonads: A Brief Review on the Mechanisms
of Biological Control
Presented byKanishendranath Sarker
Roll. VU/ Ph.D./MCB/13 No. 10 Dept. of MicrobiologyVidyasagar University
Midnapore, West Bengal, India.
Supervisors (Joint)
Dr. Pradeep Kumar Das MohapatraAsst. Prof., Dept. of Microbiology, VU, Midnapore.
Dr. Subrata DuttaAsst. Prof (Sr. Res.), Dept. Plant Pathology, BCKV, Kalyani.
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: BacteriaPhylum: ProteobacteriaClass: GammaproteobacteriaOrder: PseudomonadalesFamily: PseudomonadaceaeGenus: Pseudomonas
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
Fluorescent PseudomonadsPhytopathogenic 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…
Non-phytopathogenic, nonnecrogenic strainsP. putida
Biotype A/ Biovar A
Biotype B/ Biovar B
P. Chlororaphis
P. fluorescensBiotype 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
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
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
SIDEROPHORE PRODUCTION: The competition for Iron
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.
Biological control exerted by Production of SECONDARY METABOLITES
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)
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
The OPERON SYSTEM of different important antibiotics
The Operon systems of major antibiotics from fluorescent pseudomonads
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)
Structural genes
type 1 polyketide synthetase thio esterasehalogenasehalogenasehalogenase
transcriptional activator
Physical map of Pyoluteorin operon (Kirner et. al., 1998)
TRANSCRIPTIONAL REGULATORY MECHANISMS of synthesis of different important
Secondary Metabolites
Regulation via GacS/ GacA signal transduction pathway (Haas and Défago, 2005)
phzI
phzR
phzFABCD
AHL
o
PRNAPol
o
o
PhzI PhzR
oo o
oo
AHL-mediated Regulation
INDUCTION OF SYSTEMIC RESISTANCE: The host Immunization
Meziane et. al., 2005Leeman et. al., 1995
Meziane et. al., 2005
Ongena et. al., 2005Maurhofer et. al., 1994
De Meyer et. al., 1999
Audenaert et. al., 2002Leeman et. al., 1996
Weller et. al., 2004
References
Reports of some Bacterial traits that induce systemic resistance in host
Schematic model of the pathogen induced SAR and fluorescent pseudomonads induced ISR signal transduction pathways in Arabidopsis (Pieterse et al. 2003)
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.
THANK YOU …for listening to the Endeavor