64 J. Jani et al.
Potentiality, Mechanisms and Factors
Of Bacterial Metabolites
The antibiotics pertain to polyketides, hetero-
cyclic nitrogenous compounds and lipopeptides
have broad-spectrum action against several plant
pathogens, affecting crop plants. Secondary me-
tabolites reduce various pathogens in vitro and
some of these metabolites have been detected in
the rhizosphere (Leon et al. 2009 ). Role of bio-
control bacterial agents and their antagonistic
properties was evidenced from the comparison
of wild-type strains, non-producing insertion
or deletion mutants, and complemented deriva-
tives (Raaijmakers and Weller 1998 ; Haas and
Defago 2005 ). Moreover, shuffling of specific
genes encoding biocontrol trait to less efficient
strains in respective of particular trait may confer
or enhance biocontrol potential to non-producing
Pseudomonas respectively. Metabolites play
roles in different plant-protection mechanism,
e.g. pyoverdine in ISR and competition, and
DAPG in ISR and antagonism (Maketon et al.
2012 ). In addition, certain strains display mul-
tiple plant-beneficial traits, such as some exhibits
ACC deaminase activity and produce the phyto-
hormone indole-acetic acid, pyoverdine, DAPG
and hydrogen cyanide. The modes of action of
these secondary metabolites are partly under-
stood.
The phenazines, which are analogues of fla-
vin coenzymes, inhibit electron transport and are
known to have various pharmacological effects
on pathogenic cells (Byng et al. 1979 ). In the
presence of ferripyochelin, phenazines catalyze
the formation of hydroxyl radicals, which dam-
age lipids and other macromolecules. 2, 4-di-
acetylphloroglucinol (DAPG), Phl is the best-
known phloroglucinol compound in a family of
related. Phenazines Phl causes membrane damage
to Pythium spp. and is particularly inhibitory to
zoospores of this oomycet. Pyrrolnitrin has been
described as an inhibitor of fungal respiratory
chains. Synthetic analogues of pyrrolnitrin have
been developed for use as agricultural fungicides
(Siddiqui et al. 2006 ). Cyclic lipopeptides, which
include biocontrol-active substances have surfac-
tant properties, and are able to insert into mem-
branes and perturb their function (Groboillot
et al. 2011 ). Cyanide ion derived from HCN is a
potent inhibitor of many metalloenzymes, espe-
cially copper-containing cytochrome c oxidases.
Tryptophan-dependent IAA synthesis involved
various enzymes of Pseudomonas that help in the
development of crop plants. Apart from antibiot-
ic metabolites, it also secretes organic acids and
enzymes responsible for mineral solubilization
and antipathogenic activity (Fig. 1 ).Siderophores
Antagonism and competition may concern the
attainment of organic substrates released by
seeds and roots (Rudresh et al. 2004 ; Kamilova
et al. 2005 ) and micronutrients such as soluble
iron. Iron acquisition entails the production of
siderophores, perceptibly fluorescent pyover-
dines. Once it complexes to ferric iron in soil or
the root zone, the siderophores are then taken up
using outer membrane receptors. In a perspec-
tive of biological control, competition for iron
involves the synthesis of siderophores of higher
affinity compared with siderophores used by
phyto-pathogens (Lemanceau et al. 1992 ). Prop-
er upholding of trait and conditions can achieve
the control of pathogens by competition where
siderophore mediated iron competition may also
prevent growth of Escherichia coli O157:H7 on
food human pathogenic strain of E. coli (McKel-
lar 2007 ).