Bio-gene magnetite in organisms: its structure and putative function for orientation in the Earths magnetic field

亚铁磁性矿物磁铁矿 (Fe3O4) 以磁小体的形式存在，作为趋磁细菌的细胞内生物矿化产物，为细胞提供沿着地球磁场线游泳的能力。自 1980 年以来，有人提出，磁铁矿作为磁感受剂，在高等生物体，特别是迁徙动物的磁感中也发挥着关键作用，这在很大程度上依赖于可靠的方向感。事实上，磁小体样磁铁矿晶体是从洄游鱼类（鲑鱼、金枪鱼）的均质组织中提取的。然而，目前尚不清楚这些提取的磁铁矿晶体是否涉及磁感受器结构，因为所使用的提取技术不允许对磁铁矿晶体的细胞背景进行任何解释。最近，我们成功地从虹鳟鱼的嗅上皮中轻轻地提取和分离带有磁性内含物的完整细胞。该方法首次提供了更详细地研究这些候选磁感受器细胞的可能性。为了阐明这些磁性细胞的结构和功能，我们计划借助电子显微技术和显微拉曼光谱技术来表征磁性包裹体的内部结构、化学成分和矿物学性质。为了更深入地了解夹杂物的磁性结构，我们将使用交变场和脉冲场退磁技术测量单个单元的剩磁曲线。铁磁共振谱将用于筛选组织中与磁小体结构一致的磁性特征，以便进一步识别磁感受器细胞的候选位点。最后，我们将研究磁场变化是否会触发这些细胞的生理反应，以测试它们假定的磁感受性质。结构、磁性和生理学层面的信息将被整合到基于磁铁矿的磁接收模型中。

The ferrimagnetic mineral magnetite (Fe3O4) occurs in the form of magnetosomes as intracellular biomineralization product in magnetotactic bacteria, where it provides the cells with the ability to swim along the Earths magnetic field lines. Since 1980, it has been suggested that magnetite also plays a key role as magnetoreception agent in the magnetic sense of higher organisms, particularly of migratory animals, which critically depend on a reliable sense of orientation. Indeed, magnetosome-like magnetite crystals were extracted from homogenized tissues of migratory fish species (salmon, tuna). However, it is still not clear whether these extracted magnetite crystals are involved in a magnetoreceptor structure, since the extraction technique used does not allow any interpretation on the cellular context of the magnetite crystals. Recently we succeeded in our efforts to gently extract and isolate intact cells with magnetic inclusions from the olfactory epithelium of rainbow trout. This method provides for the first time the possibility to study these candidate magnetoreceptor cells in more detail. In order to clarify the structure and function of these magnetic cells, we are planning to characterize the magnetic inclusions in terms of inner architecture, chemical composition and mineralogical nature with the aid of electron-micrographic techniques and micro-Raman-spectroscopy. In order to gain more insight into the magnetic structure of the inclusions, we will measure magnetic remanence curves of individual cells using alternating-field and pulse-field demagnetization techniques. Ferromagnetic resonance spectra will be used to screen tissue for magnetic signatures consistent with magnetosome structures in order to identify further candidate sites for magnetorceptor cells. Finally, we will investigate if magnetic field changes trigger physiological responses in these cells to test their putative magnetoreceptive nature. The information grained on the levels of structure, magnetism, and physiology, will be combined into a model of magnetite-based magnetoreception.