Physicochemical Properties of Phosphate-Doped Ferrihydrite Mineral: Implications in Understanding Ferritin Iron Core and Bacterial Growth

Abstract

Iron, a crucial element, is inextricably intertwined in various stages of living and non- living systems. Its existence in two different oxidation states (Fe2+/Fe3+) is not only a virtue (involvement in electron transfer) but also troublesome (low solubility of Fe3+ at neutral pH and Fenton’s reaction by Fe2+). As a solution to this essentiality and toxicity dilemma, nature devised a globular multimeric protein nanocage; ferritin to detoxify and store iron in soluble ferrihydrite bio-mineral form. Native ferritin bio-minerals are associated selectively with variable amounts of phosphate depending upon their source, for instance in animals Pi: Fe ~0.1 and in plant and bacteria Pi: Fe ~0.5 -1.0, which possibly contributes to their physicochemical properties. Similarly, in nature among various impurities, phosphate adsorption on ferrihydrite is verily observed. Therefore, a comparison of bare and protein-encapsulated phosphate-doped iron minerals may give insights on impact of phosphate on structure, stability and reactivity of iron bio-mineral. So a detailed investigation was performed on number of phosphate-doped ferrihydrite with varied ratios of Pi and Fe, which closely resembles, iron mineral found in animals, plants, and nature. The doped ferrihydrite having almost equal ratios of Pi and Fe exhibited a phase transition with minimal water of crystallization (amorphous nature of the mineral), showed the highest amount of iron release both in the reductive and non-reductive pathway, and also promoted bacterial growth. Hence, the current work justifies the association of phosphate with native ferrihydrite minerals in different proportions.