Abstract Synergisms between microbial exudates on Fe (hydr)oxide dissolution as an effective Fe acquisition pathway have been recently addressed and vigorously debated. However, Fe liberation mechanisms and where siderophores and phosphorus (P) coexist received little attentions. Current study systematically investigated ferrihydrite dissolution in the presence of desferrioxamine B (DFOB) (a kind of fungally-derived siderophores) and inorganic/organic phosphorus (orthophosphate, Pi; myo-inositol hexaphosphate, IHP), as a function of solute pH, reaction time and reagent content. Reacted solids were characterized by N2-BET adsorption, zeta (ζ) potential analysis, sequential extraction analysis (SEDEX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Our results indicate that upon reaction with P-only or (DFOB + P) systems, interfacial complexation partially switched from monolayer bidentate-binuclear surface complexes to ternary complexes, or laterally transformed into amorphous Fe-P precipitates. The Fe-Pi complex precipitated more readily under acidic conditions, and Fe-IHP complex preferentially nucleated in neutral-alkaline environments. Phosphorus slightly promoted Fe release from minerals and fixation to the leached layer or interfacial liquid zone initially, but subsequently prevented further attacks from protons and DFOB. The co-effects of P and DFOB likely correspond to two successive scenarios: 1) DFOB is preferentially attracted toward ferrihydrite surfaces by negative electrical fields induced by adsorbed phosphorus and can act synergistically with labile P-Fe complexes, resulting in intensive temporal dissolution of Fh; 2) subsequent Fe shuttling to DFOB can be prohibited by stabilized, passive P/Fe-P layers. Our results emphasize the antagonism between P compounds and siderophores (i.e., DFOB here) on ferrihydrite dissolution to improve understanding of the biologically-mediated Fe cycling in natural systems.

中文翻译：

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磷/铁载体系统中铁循环的系统研究：协同还是拮抗？

摘要 微生物渗出物对 Fe（氢氧化物）溶解作为有效的 Fe 获取途径之间的协同作用最近得到了解决和激烈争论。然而，Fe 释放机制以及铁载体和磷 (P) 共存的地方很少受到关注。目前的研究系统地研究了在去铁胺 B (DFOB)（一种真菌衍生的铁载体）和无机/有机磷（正磷酸盐，Pi；肌醇六磷酸盐，IHP）存在下，作为溶质 pH、反应的函数的水铁矿溶解时间和试剂含量。通过 N2-BET 吸附、zeta (ζ) 电位分析、顺序萃取分析 (SEDEX)、场发射扫描电子显微镜 (FESEM)、高分辨率透射电子显微镜 (HRTEM)、X 射线衍射 (XRD) 表征反应的固体, X 射线光电子能谱 (XPS)、微拉曼光谱和衰减全反射傅立叶变换红外光谱 (ATR-FTIR)。我们的结果表明，在与 P-only 或 (DFOB + P) 系统反应时，界面络合部分从单层双齿双核表面复合物转变为三元复合物，或横向转变为无定形 Fe-P 沉淀物。Fe-Pi 复合物在酸性条件下更容易沉淀，Fe-IHP 复合物优先在中性碱性环境中成核。磷最初略微促进了铁从矿物中释放并固定到浸出层或界面液体区，但随后阻止了质子和 DFOB 的进一步攻击。P 和 DFOB 的共同效应可能对应于两个连续的场景：1) DFOB 被吸附的磷诱导的负电场优先吸引到水铁矿表面，并且可以与不稳定的 P-Fe 配合物协同作用，导致 Fh 的强烈时间溶解；2) 稳定的被动 P/Fe-P 层可以禁止随后的 Fe 穿梭到 DFOB。我们的结果强调了 P 化合物和铁载体（即这里的 DFOB）对水铁矿溶解的拮抗作用，以提高对自然系统中生物介导的 Fe 循环的理解。