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.

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