Pseudomonas bacteria are root colonizing bacteria that produce antimicrobial compounds to control plant pathogens through quorum sensing. They assess their population density through signaling molecules and coordinate metabolic activities accordingly. The antimicrobial compounds produced include 2,4-diacetylphloroglucinol, polyteorin, phenazines, acyl homoserine lactones, hydrogen cyanide, and cyclic lipopeptides. These compounds are produced through density-dependent regulation and help pseudomonas suppress disease-causing pathogens while also promoting plant growth.

1. Pseudomonas
As a biocontrol agent

2. Introduction
• Pesudomonas are root colonizing fluroscent
bacteria present in rhizosphere.
• All free living bacteria communicate with one
another by synthesizing , secretion & sensing
signal molecules ,which diffuse in
environment are detected by specific cellular
receptor ,this is known as quorum sensing.

3. Continued………
• It is assumed that signaling enable to produce
bacterial to asses their microbial population and
densities.
• This signals are to be coordinate metabolic
activities &developed bacterial population.
• Pseudomonas produces antimicrobial compound
which are produced under cell population density
dependent auto induction control acting at
transcriptional & post transcriptional levels.

4. Continued………………………….
• This regulation can either be stimulated
/inhibited by variety of chemical signals
produced by pseudomanas themselves.
• Along with biocontrol agent ,pseudomanas
also act as plant growth promoting bacteria &
suppress phytopathogens.

5. Mechanism
• They produce antimicrobial factors such as
antibiotics.
• They metabolites or degrade virulense factor
in pathogens .
• They compete with bacterial/fungal pathogen
for nutrition & space.

6. The antimicrobial factors produced by
pseudomonas are :
1. 2,4-diacetylphloroglucinol (DAPG):-
it is particularly important in
the suppression of roots disease caused by
thiclauiopsis blasicola ,pythium ultimum etc
• DAPG includes its own biosynthesis via
autoinduction mechenism.

7. Continued…………………
2. Polyteorin
• It kills oomycetes pythium ultinum.
• It induces its own biosynthesis pathways via
autoinduction mechenism.
• The DAPG & PLT biosynthesis pathways
enable the bacteria to maintain production
of these key antibiotic at balanced levels.

8. Continued…
• 3. phenazines
• Phenazines are colored heterocytes derived
from chorismate .
• They are synthesized by gram negative &
positive bacteria.
• Phenazine -1-carboxylic acid is primary
product of pheanzine operon.

9. Also………
4. Acyl homoserine lactones
• AHL regulates phenazine operon on roots & can
serve as inter populations signals in the wheat
rhizosphere.
5. Hydrogen cyanide
• HCN is an inhibitors of metaloenzymes in
particular of most terminal oxidases.
6. Cyclic lipopeptides
• At high conc. They are deterimental to integrity
of phospholipid membrane in various organism.