Ferrichrysin siderophore from gangetic Aspergillus japonicus: Isolation, Characterization, and role in sustained...

Arsenic is a highly toxic metalloid and a major environmental contaminant of global concern. Indo-Gangetic plain is among the most arsenic affected regions. The groundwater arsenic level across the Indo-Gangetic plain of Bihar and West Bengal is known to exceed permissible limits. Bioremediation presents a sustainable and eco-friendly alternative to conventional remediation techniques where microorganisms or their metabolic products like siderophores can be used for detoxifying the contaminants. In this study, a fungal isolate obtained from Gangetic water was identified as Aspergillus japonicus. The isolate exhibited tolerance up to 3000 mg L⁻¹ of arsenate (As⁵⁺) and 750 mg L⁻¹ of arsenite (As³⁺), while maintaining the ability to produce siderophores even under arsenic stress. The isolated siderophore was identified as ferrichrysin, a hydroxamate siderophore using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) showing m/z ~ 821.31 corresponding to [M + NH₄]⁺ adduct of ferrichrysin. Ferrichrysin's arsenic-binding potential was evaluated by modified chrome azurol S (CAS) assay where ferrichrysin caused 84.5% discoloration of the CAS/As reagent. Molecular docking revealed stable complexes of ferrichrysin with arsenate and arsenite with E_total i.e. docking scores of -103.72 and - 91.80 respectively. These findings were further substantiated by Density Functional Theory (DFT) analysis which confirmed binding of ferrichrysin with arsenic. Overall, this study provides experimental as well as orbital analysis based electronic confirmation of arsenic chelation ability of purified fungal hydroxamate siderophore. This further establishes the parallelism of this secondary metabolite production in arsenic tolerance of the fungus. This work represents a preliminary investigation focusing on the mechanistic and analytical aspects of siderophore-arsenic interaction. Further studies are required to evaluate its practical efficacy and feasibility as a bioremediation agent under field conditions.