Biomineralization of Fe³⁺ to Nanosized γFe₂O₃ by Haloferax alexandrinus GUSF-1

Abstract

Hypersaline environment is a habitat with extreme osmotic conditions along with low A_w, serving as a home to extremely halophilic and halotolerant bacteria. The hypersaline environments, such as solar salterns located along the rivers, are exposed to fluxes of iron from iron ore transportation and other industrial wastes. The solar salterns often serve as a sink for metal intoxicants. Studies on archaea interaction with metal ions indicate the formation of minerals such as goethite, hematite, rhodochrosite, etc. However, studies exploring haloarchaeal candidates interacting with metals such as Fe³⁺ in a hypersaline growth condition are scarce. This study unveils for the first time formation of γFe₂O₃ from Fe³⁺ by the haloarchaeon, Haloferax sp. GUSF-1 thus implying the significance of the culture synthesizing minerals in hypersaline sediments. γFe₂O₃ is formed from Fe³⁺ by the haloarchaeon Haloferax sp. GUSF-1 (GenBank accession no.GU-1KF796625), under microaerophilic growth on sodium acetate. A 50 mg L⁻¹ of Fe²⁺ and 30.6 mg L⁻¹ of Fe³⁺ was detected inside the cells. Simultaneously, a brown-colored crystalline material deposited in the culture broth through an iron reductase inhibited by Zn²⁺ ions. The XRD of the deposit exhibited d values of 2.96, 2.514, 2.086, 1.6, and 1.45, while SEM-EDX displayed cubic and irregularly shaped minute particles with peaks for Fe at 0.6, 6.4, and 6.6 keV, respectively. TEM profiles revealed polycrystalline particles of 12–23 nm in size. Further, the SAED concentric pattern of light scattering with well-defined diffraction spots was consistent and matched with maghemite's crystal structure (γFe₂O₃). The FTIR spectrum revealed a peak at 1450 cm⁻¹ indicating iron oxyhydroxide formation as an intermediate having γ-FeOOH stretching bond vibrations. Conclusively, this study opens the possibility of the haloarchaea isolated from solar salterns for its exploitation in nanobiotechnology.

Keywords:

• Archaea
• ferric reductase
• Haloferax sp. GUSF-1
• maghemite

Acknowledgments

The authors are indebted to Dr. M. Shyamprasad and Mr.V. Khedekar, National Institute of Oceanography, Goa, India, for extending the SEM-EDX facility and Mr. G Prabhu for XRD profiling. We also thank the Indian Institute of Technology, Bombay, on for the TEM facility.

Disclosure statement

No potential conflict of interest was reported by the author(s).