Agriculture Reference
In-Depth Information
by PS bacteria and their consequential impact on plant pathogens are discussed
briefly in the following section.
Role of Siderophores in Disease Suppression
Iron is one of the most important nutrients for both eukaryotes (Sayyed et al.
2007a
,
b
) and nearly all prokaryotes (Kaplan and Kaplan
2009
) which play fundamental
roles in both iron metabolism and virulence of most fungi. Some of the crucial
functions of iron in different metabolism include (1) transport, storage, and activa-
tion of molecular oxygen and amino acid syntheses, (2) respiration, (3) DNA
biosynthesis, (4) nitrogen fixation, (5) reduction of ribonucleotides and dinitrogen,
and (6) activation and decomposition of peroxides and electron transport (Duhan
et al.
1998
; Faraldo-Gomez and Sansom
2003
; Katiyar and Goel
2004
; Miethke and
Marahiel
2007
; Sandy and Butler
2009
). However, when iron concentration in the
environment is reduced, the growth of organisms requiring such element is
inhibited. Under iron-starved conditions, numerous prokaryotes including bacteria
such as
Chryseobacterium
sp. (Radzki et al.
2013
),
Pseudomonas
sp. (Babana
et al.
2013
),
Pantoea agglomerans
and
Burkholderia anthina
(Walpola and Yoon
2013
), and
P. fluorescens
(Parani and Saha
2012
); fungi such as
A. fumigatus
and
A. nidulans
(Gr¨ndlinger et al.
2013
); and actinomycetes
Streptomycetes
spp. (Das
et al. 2007), however, synthesize a wide range of siderophores (a Greek phrase for
“iron bearer”), a relatively low molecular weight (below 2 kDa), ferric ion-specific
chelating agents (Neilands
1995
; Budzikiewicz et al.
2010
) in order to solubilize,
capture, and transport inorganic iron to the cell (Carrillo-Castaneda et al.
2005
;
Sandy and Butler
2009
). Some of the common siderophores produced by many
fungi include ferrichromes by
Aspergillus
spp. (Charlang et al.
1981
),
Suillus
variegatus
(Wallander and Wickman
1999
), and
Microsporum
spp. (Bentley
et al.
2008
); coprogens by
Fusarium dimerum
(Van der Helm and Winkelmann
1994
) and
Epicoccum purpurascens
(Frederick et al.
1981
); and fusigen by
Fusar-
ium
spp. (Van der Helm and Winkelmann
1994
) and
Histoplasma capsulatum
(Burt
1982
). Siderophores produced by many organisms play some vital roles, for
example, it functions as plant growth promoters (Yadav et al.
2011
; Gamit and
Tank
2014
), biocontrol agents (Arora et al.
2001
; Schenk et al.
2012
), and biore-
mediation agents (Wang et al.
2011
; Ishimaru et al.
2012
), in addition to their
valuable role in soil mineral weathering (Reichard et al.
2005
; Buss et al.
2007
;
Shirvani and Nourbakhsh
2010
). Realizing these properties, siderophore-positive
strains have been exploited in the management of plant diseases (Kloepper
et al.
1980
; Wong et al.
1996
; Sindhu et al.
1997
; Sritharan
2000
; Verma
et al.
2011
). The siderophoregenic rhizobacteria inhabiting soil/rhizospheres pro-
tect the plants from damage by preventing the iron acquisition by phytopathogens
(Lemanceau and Albouvette
1993
; Estrella and Chet
1998
; Bloemberg and
Lugtenberg
2001
; Johri et al.
2003
). Apart from iron, siderophores also form
complex with heavy metals such as Cd, Pb, Ni, As (III, V), Al, Zn, Cu, Co, and
Sr (Nair et al.
2006
; Sayyed and Chincholkar
2010
). Therefore, iron-deficient
