Metabolites of Pseudomonads: A New Avenue of Plant Health Management 67
activity. Notz ( 2001 ) checked the effects of four
different crops as biotic factor on the expres-
sion of Phl genes and colonization of P f CHAO.
Maximum expression of Phluoroglucinol and
colonization of culture was exhibited in maize
plant. On the other side in absence of adequate
colonization posses diminish biocontrol activity.
It is well reported an inversely proportional rela-
tion between the numbers of bacteria present on
the wheat root and the number of take-all lesions
seen on the plant (Schippers et al. 1987 ; Bull
et al. 1993 ). However, reports also claim absence
of any effects of colonization on biocontrol ac-
tivities of bacteria (Roberts et al. 1994 ).
It is also desired to document the impact of
the deviated expression of such metabolites on
native rhizospheric microflora. During the study
of impact of the wild type P. fluorescens strain
CHA0-Rif and CHA0-Rif/pME3424 which is a
Phl− and Pyoluteorin overproducing derivative
on the indigenous culturable bacterial and fungal
populations in the cucumber rhizosphere has been
investigated. Compared with untreated plants,
Natsch et al. ( 1998 ) demonstrated that neither
CHA0-Rif nor CHA0-Rif/pME3424 affected the
frequency of dominant bacterial groups, whereas
Girlanda et al. ( 2001 ) observed a detectable in-
fluence on the culturable fungal population.
Among all metabolites of Pseudomonas spp.
Pyoverdin, Pyoluteorin and Phluoroglucinol
(Phl) studied as major metabolites to control fun-
gal disease on crops. Phluoroglucinol efficiently
contributes in control of Caenorhabditis elegans
and other nematodes. Expression of the metabo-
lite depends on biotic and abiotic factors/condi-
tions. Biocontrol Pseudomonads are not specific
for one plant. The composition of root exudates is
species and cultivar specific and the differences
in their quantity and/or quality can modulate the
production of metabolites. In addition, the role
of intra-species and inter-species signalling is the
fruitful aspect as a scientific research with equal-
ly relevant applications. For example, increasing
understanding of the role of N-acyl homoserine
lactone (NAHL) signal molecules in antifungal
metabolite production and the identification of
promoters that can be induced in the rhizosphere
is providing new approaches for the development
of novel biocontrol agents.References
Angayarkanni T, Kamalakannan A, Santhini E, Predeepa
D (2005) Identification of biochemical markers for the
selection of Pseudomonas fluorescens against Pythium
spp. In: Asian conference on emerging trends in plant-
miceobial interactions. University of Madras, Chennai
Arima K, Imanaki H, Kousaka M, Fukuta A, Tamura
G (1964) Pyrrolnitrin, a new antibiotic substance,
produced by Psneudomonas. Agric Biol Chem
28:575–576
Arima K, Imanaki H, Kousaka M, Fukuda A, Tamura
G (1965) Studies on pyrrolnitrin a new antibiotic. I.
Isolation and properties of pyrrolnitrin. J Antibiot A
18:201–204
Bakker PAHM, Pieterse CMJ, van Loon LC (2007)
Induced systemic resistance by fluorescent Pseudo-
monas spp. Phytopathology 97:239–243
Bjornlund L, Ronn R, Pechy-Tarr M, Maurhofer M, Keel
C, Nybroe O (2009) Functional GacS in Pseudomonas
DSS73 prevents digestion by Caenorhabditis elegans
and protects the nematode from killer flagellates.
ISME J 3:770–779
Blaha D, Prigent-Combaret C, Mirza MS, Moenne-Loc-
coz Y (2006) Phylogeny of the 1-aminocyclopropane-
1-carboxylic acid deaminase encoding gene acdS in
phyto beneficial and pathogenic Proteobacteriaand
relation with strain biogeography. FEMS Microbiol
Ecol 56: 455–470
Bull CT, Weller DM, Thomashow LS (1993) In situ
measurement of root respiration and soluble C-con-
centrations in the rhizosphere. Soil Biol Biochem
25:1189–96
Byng G, Eustice DC, Jensen RA (1979) Biosynthesis of
Phenazine pigments in mutant and wild-type cultures
of Pseudomonas aeruginosa. J bacteriol 13:884–86
De Mesel I Derycke S Moens T Van Der Gucht K Vincx
M Swings J (2004) Top-down impact of bacterivorous
nematodes onthe bacterial community structure: a
microcosm study. Environ Microbiol 6:733–744
Diby P, Saju K., Jisha PJ, Sharma YR, Kumar A, Anandraj
M (2005) Pseudomonas fluorescens mediated vigour
in black pepper ( Piper nigrum L). Ann of Micro
55:129–133
Dikin A, Sijam K, Kadir J, Seman IA (2007) Mode of
action of antimicrobial substances from Burkholderia
multivorans and Microbacterium testaceum against
Schizophyllum commune Fr. Int J Agri Biol 9:311–314
Frias JE, Flores E, Herrero A (1994) Requirement of the
regulatory protein NtcA for the expression of nitrogen
assimilation and heterocyst development genes in the
cyanobacterium Anabaena sp. PCC 7120. Mol Micro-
biol 14:823–32