143
the ability to bind different iron moieties, and the siderophores vary based on their
affinity toward iron (Aznar and Dellagi 2015). Among the fungal organisms,
Saccharomyces cerevisiae, Cryptococcus neoformans, and Candida albicans lack
the production of siderophores and instead utilize the siderophores produced by
other organisms; those are called xenosiderophores. Moreover, these organisms
undertake RIA, heme-bound iron, and low-affinity iron uptake mechanism (Kaplan
and Kaplan 2009).
The presence of ferrichromes, the coprogens, and fusigen siderophores was
abundant among fungal species, as well. Ahmed and Holmstrom (2014) reported
that the polished mineral surfaces highly influence the production of siderophores at
higher concentration than the minerals surrounding bulk soil. Recently, a novel
metachelin A (O-glycosylated and N-oxidized coprogen) and metachelin B
(O-glycosylated) and a coprogen-type siderophore were identified from the insectpathogenic fungus Metarhizium robertsii (Krasnoff et al. 2014).
9.3 Fungal Siderophore Synthesis and Function
Synthesis of siderophores both in fungi and bacteria is similar (non-ribosomal peptide synthetase, NRPS), but differs with a unique fungal siderophore transporter
(SIT) uptake mechanism (Sorensen et al. 2014). After uptake, iron-free siderophores
are hydrolyzed and recycled by the cellular vesicles (Sorensen et al. 2014). The
presence of siderophore transporters (SIT) exclusively in fungi enhances the uptake
of different types of small chelators and secures their own needs of iron requirement
from the bacterial uptake (Saha et al. 2013).
Boyce and Andrianopoulos (2015) have reviewed the genes responsible for the
biosynthesis of siderophores and their ability to acquire iron from the host critically
for intracellular growth. So far, genes responsible for siderophore biosynthesis are
identified from Ustilago maydis (sid1) (Mei et al. 1993), Aspergillus nidulans (sidA)
(Eisendle et al. 2003), A. oryzae (dffA) (Yamada et al. 2003), A. fumigatus (sidA)
(Schrettl et al. 2004), Fusarium graminearum (SID1) (Greenshields et al. 2007),
Cochliobolus heterostrophus (SIDA) (Turgeon et al. 2008), and Rhizophagus irregularis (Tamayo et al. 2014). Moreover, the genes regulating the homeostasis in the
organisms, viz., C. albicans, Aspergillus sp., and Cr. neoformans, are explained by
Chen et al. (2014).
Different types of siderophores are produced by the fungus with each performing
its respective functions like extracellular iron acquisition, intracellular iron storage,
conidial iron acquisition, as well as storage during infections. These different siderophores are encoded by different gene sequences, where the study on silencing
the siderophore-producing genes of A. fumigatus prevented the infections in murine
models of pulmonary aspergillosis (Bills et al. 2014). The intracellular and extracellular siderophores are mostly produced through the genes of non-ribosomal peptide
synthetases (NPS), where Oide and his colleagues (2015) pointed the importance
and function of the genes NPS1, NPS2, and NPS6 in cereal pathogen F. graminearum,
9 Fungal Siderophores: Prospects and Applications
the ability to bind different iron moieties, and the siderophores vary based on their
affinity toward iron (Aznar and Dellagi 2015). Among the fungal organisms,
Saccharomyces cerevisiae, Cryptococcus neoformans, and Candida albicans lack
the production of siderophores and instead utilize the siderophores produced by
other organisms; those are called xenosiderophores. Moreover, these organisms
undertake RIA, heme-bound iron, and low-affinity iron uptake mechanism (Kaplan
and Kaplan 2009).
The presence of ferrichromes, the coprogens, and fusigen siderophores was
abundant among fungal species, as well. Ahmed and Holmstrom (2014) reported
that the polished mineral surfaces highly influence the production of siderophores at
higher concentration than the minerals surrounding bulk soil. Recently, a novel
metachelin A (O-glycosylated and N-oxidized coprogen) and metachelin B
(O-glycosylated) and a coprogen-type siderophore were identified from the insectpathogenic fungus Metarhizium robertsii (Krasnoff et al. 2014).
9.3 Fungal Siderophore Synthesis and Function
Synthesis of siderophores both in fungi and bacteria is similar (non-ribosomal peptide synthetase, NRPS), but differs with a unique fungal siderophore transporter
(SIT) uptake mechanism (Sorensen et al. 2014). After uptake, iron-free siderophores
are hydrolyzed and recycled by the cellular vesicles (Sorensen et al. 2014). The
presence of siderophore transporters (SIT) exclusively in fungi enhances the uptake
of different types of small chelators and secures their own needs of iron requirement
from the bacterial uptake (Saha et al. 2013).
Boyce and Andrianopoulos (2015) have reviewed the genes responsible for the
biosynthesis of siderophores and their ability to acquire iron from the host critically
for intracellular growth. So far, genes responsible for siderophore biosynthesis are
identified from Ustilago maydis (sid1) (Mei et al. 1993), Aspergillus nidulans (sidA)
(Eisendle et al. 2003), A. oryzae (dffA) (Yamada et al. 2003), A. fumigatus (sidA)
(Schrettl et al. 2004), Fusarium graminearum (SID1) (Greenshields et al. 2007),
Cochliobolus heterostrophus (SIDA) (Turgeon et al. 2008), and Rhizophagus irregularis (Tamayo et al. 2014). Moreover, the genes regulating the homeostasis in the
organisms, viz., C. albicans, Aspergillus sp., and Cr. neoformans, are explained by
Chen et al. (2014).
Different types of siderophores are produced by the fungus with each performing
its respective functions like extracellular iron acquisition, intracellular iron storage,
conidial iron acquisition, as well as storage during infections. These different siderophores are encoded by different gene sequences, where the study on silencing
the siderophore-producing genes of A. fumigatus prevented the infections in murine
models of pulmonary aspergillosis (Bills et al. 2014). The intracellular and extracellular siderophores are mostly produced through the genes of non-ribosomal peptide
synthetases (NPS), where Oide and his colleagues (2015) pointed the importance
and function of the genes NPS1, NPS2, and NPS6 in cereal pathogen F. graminearum,
9 Fungal Siderophores: Prospects and Applications