Greigite or magnetite: Environmental and genetic determinants controlling biomineralization in magnetotactic bacteria

生物形成的各种材料，即使是在生理条件下用有限的元素制成的，也往往比类似的人造材料具有优越的性能。趋磁细菌中的磁小体链代表了这种生物材料的生物学范式，其中具有受控特性的磁性纳米晶体在称为磁小体的细胞器中合成并排列成线性链。这些链使细胞沿着地球的磁力线排列。磁小体由磁铁矿[Fe(II)Fe(III)2O4]或灰长岩[Fe(II)Fe(III)2S4]晶体嵌入脂质囊泡中构成。直到最近，在纯培养中只有能产生磁铁矿的菌株。因此，近年来，这些菌株的生物矿化机制的分子和物理化学知识稳步发展，但对灰长铁矿矿化细菌的生物矿化机制却严重滞后。随着一种新型细胞BW-1的分离，我们现在有了一种模式生物，它既能形成磁铁矿，也能形成灰铁矿。因此，在本项目中，我们提出了一种综合的多学科方法来了解趋磁细菌中的灰长岩生物矿化。我们将特别研究有利于产生磁铁矿或灰长岩的环境条件，以及导致BW-1菌株中每种磁铁矿和灰长岩形成的化学反应途径。此外，我们将确定生物矿化过程中涉及的生物决定因素，特别关注氧化还原蛋白，如最近发现的磁色素。最后，我们将在体外矿化实验中使用这种生物决定因素来测试其在仿生实验中的作用。我们的结果将对体内生物矿化的基本理解具有直接的相关性。此外，我们预计我们的结果将成为对生物添加剂在烧杯中磁性纳米颗粒控制中的作用进行更定量描述的起点。

There is a variety of materials formed by organisms, which often have superior properties than similar man-made materials, even if they are made with a limited amount of elements and under physiological conditions. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such a biological material, where magnetic nanocrystals with controlled properties are synthesized in organelles called magnetosomes and arranged into linear chains. These chains serve the cells to align along the Earth's magnetic field lines. The magnetosomes are made of a magnetite [Fe(II)Fe(III)2O4] or greigite [Fe(II)Fe(III)2S4] crystal embedded in a lipidic vesicle. Until recently, only magnetite-building strains were available in pure culture. Thus, the molecular and physico-chemical knowledge of the biomineralization mechanism steadily advanced in the recent years for those strains, but dramatically lags behind for greigite-mineralizing bacteria. With the isolation of a new type of cells, BW-1, we now have a model organism in our hands, which is able to form both magnetite and greigite. In this project, we thus propose an integrated and multidisciplinary approach to understand greigite biomineralization in magnetotactic bacteria. We will in particular study the environmental condition favoring the production of magnetite or greigite as well as the chemical reaction pathway leading to the formation of each magnetite and greigite in this BW-1 strain. In addition, we will determine what are the biological determinants involved in the biomineralization process with a particular focus on redox proteins such as the recently discovered magnetochrome. Finally, we will use this biological determinant in in vitro mineralization experiments to test their effect in biomimetic experiments. Our results will be of immediate relevance for the fundamental understanding of biomineralization in vivo. In addition, we anticipate our outcomes to be the starting point towards a more quantitative description of the role biological additives can have on the control of magnetic nanoparticles in the beaker.