Fungal Siderophore: Biosynthesis, Transport, Regulation, and Potential Applications

Iron (Fe) is an essential nutrient for life and the fourth most abundant element in the earth. The availability of ferric iron (Fe III) is less in soil solution due to the low solubility of ferric hydroxides, oxides, and oxyhydroxides. Therefore, the Fe availability to microbes and plants is limited, albeit its abundance in the environment. Therefore, the availability of Fe to microbes and plants has evolved strategies based on acidification through proton extrusion and organic acid production, chelation, ligands like siderophore and phytosiderophore production, and enzymatic reduction involving reductase enzymes. This review attempts to explain the fungal siderophore, its biosynthesis, transport, and practical application. Thus, siderophore is an iron-binding molecule synthesized by fungi, bacteria, cyanobacteria, and plants. The common types of siderophore are hydroxamates, catecholates, carboxylates, but hydroxamate type is dominant in fungi. L-ornithine is a biosynthetic precursor of siderophore and synthesized through multimodular large enzymes complex nonribosomal peptide synthetase (NRPSs) dependent/independent. Siderophore-Fe chelators protein (FIT1, FIT2, and FIT3) helps in the retention of siderophore. Saccharomyces cerevisiae expresses two genetically separate systems (reductive and a non-reductive system) at the plasma membrane, which converts Fe III into Fe II by ferrous-specific metallo-reductases enzyme complex, FRE reductases. Regulation of the siderophore gene expression on the promoter region by Fur Box protein depends on the availability of Fe in the external medium. Biotechnologically, it is more important due to its wide range of applications that include medical, remediation of heavy metal, biocontrol of plant pathogens, and enzyme inhibitions.