Elucidating the structure of novel cyanobacterial siderophore produced by Anabaena oryzae and its implication in removal of cadmium

Abstract

Cyanobacteria, a group of prokaryotic photoautotrophs, are accredited for trace metal sequestration due to their ability to produce various siderophores and are widely utilised for bioremediation. In this context, we investigated the ability of cyanobacterium Anabaena oryzae for removal of cadmium. Cadmium toxicity disrupts crucial physiological processes in photosynthetic organisms, inhibits growth, reduces photosynthetic efficiency, etc. thereby, truncating nutrient cycling. Structural elucidation of siderophore produced by A. oryzae through FTIR, mass spectrometry, 1D and 2D NMR (COSY, HSQC and NOESY) depicted tetradentate denticity and conspicuous presence of dihydroxamate along with unique spatial arrangement of atoms, conferring novel structure. Furthermore, the physiological and biochemical studies by administering iron and cadmium, individually as well as in combinations, exhibited cadmium-mediated toxicity in the cyanobacterium, ultimately reducing physiological capacity, whereas iron possessed ameliorating effect. Nevertheless, the possibility of Cd-induced siderophore production was shown by higher production of siderophore in presence of cadmium. Proteome profiling further displayed regulation of siderophore synthesis through cadmium supplementation. Moreover, negative binding energies of transporter proteins like OmpA, Pbp, ABC type-transporter and TonB with siderophore-Cd complex, shown by in silico docking studies, suggested uptake and thereby removal of cadmium by A. oryzae. This study addresses the problem of cadmium toxicity in cyanobacteria and explores the potential of A. oryzae to mitigate this toxicity through siderophore production and metal removal. It also contributes to the understanding of siderophore-mediated metal sequestration and introduces a novel siderophore candidate with promising prospects for cadmium remediation.