Genetic and Ultrastructural Analysis Reveals the Key Players and Initial Steps of Bacterial Magnetosome Membrane Biogenesis.
Genetic and Ultrastructural Analysis Reveals the Key Players and Initial Steps of Bacterial Magnetosome Membrane Biogenesis.
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DOI：
10.1371/journal.pgen.1006101
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发表时间：
2016-06
期刊：
影响因子：
4.5
通讯作者：
Schüler D
中科院分区：
文献类型：
--
作者：
Raschdorf O;Forstner Y;Kolinko I;Uebe R;Plitzko JM;Schüler D
趋磁细菌的磁小体含有有序的纳米晶体，用于磁导航，最近已成为研究原核生物中膜结合细胞器形成的最复杂的模型系统。磁小体生物合成被认为开始于一个专门的隔室，磁小体膜（MM）的形成，其中磁性矿物的生物合成受到严格控制。虽然磁小体的生物矿化及其随后组装成线性链最近已经越来越好地研究，但MM形成的分子机制和早期阶段仍然知之甚少。在Alphaproteobacterium Magnetoelillum gryphiswaldense中，发现大约30个基因控制磁小体生物合成。通过几个关键突变株的冷冻电子断层扫描，我们确定了该模式生物中控制MM形成的基因互补。而推定的磁小体铁转运蛋白MamB是最关键的过程，并导致最严重的MM表型消除后，MamM，MamQ和MamL也需要形成野生型样MM。合成操纵子中组合的七个基因子集（mamLQBIEMO）足以在缺乏关键mamAB操纵子的其他基因的情况下恢复细胞内膜的形成。跟踪从头磁小体膜形成的遗传诱导显示，磁小体起源于非特异性细胞质膜位置之前对齐成连贯的链。我们的研究结果表明，没有一个单一的因素是必不可少的MM形成，而是精心策划的几个磁小体蛋白的累积作用。膜结合原核细胞器最有趣的例子之一是磁小体，它由形状完美的磁性纳米晶体组成的有序链组成，在许多水生细菌中，磁小体作为地磁场传感器，引导它们游向天然沃茨底部的缺氧区。在模型细菌Gryphiswaldense磁小体和相关的趋磁微生物中，磁小体是通过由30多个基因协调的复杂途径形成的。然而，磁小体生物合成的初始和最关键的步骤，形成和分化的一个专门的细胞内膜隔室控制生物矿化的磁铁矿晶体，仍然知之甚少。通过对几个突变体的超微结构分析和磁小体从头合成的遗传诱导，我们确定了磁小体膜生物合成的关键决定因素和早期步骤。我们的研究结果表明，在细菌中的细胞内膜的形成是由几个因素的累积作用介导的，但显然是不同的控制比真核细胞中的细胞内膜重塑。
Magnetosomes of magnetotactic bacteria contain well-ordered nanocrystals for magnetic navigation and have recently emerged as the most sophisticated model system to study the formation of membrane bounded organelles in prokaryotes. Magnetosome biosynthesis is thought to begin with the formation of a dedicated compartment, the magnetosome membrane (MM), in which the biosynthesis of a magnetic mineral is strictly controlled. While the biomineralization of magnetosomes and their subsequent assembly into linear chains recently have become increasingly well studied, the molecular mechanisms and early stages involved in MM formation remained poorly understood. In the Alphaproteobacterium Magnetospirillum gryphiswaldense, approximately 30 genes were found to control magnetosome biosynthesis. By cryo-electron tomography of several key mutant strains we identified the gene complement controlling MM formation in this model organism. Whereas the putative magnetosomal iron transporter MamB was most crucial for the process and caused the most severe MM phenotype upon elimination, MamM, MamQ and MamL were also required for the formation of wild-type-like MMs. A subset of seven genes (mamLQBIEMO) combined within a synthetic operon was sufficient to restore the formation of intracellular membranes in the absence of other genes from the key mamAB operon. Tracking of de novo magnetosome membrane formation by genetic induction revealed that magnetosomes originate from unspecific cytoplasmic membrane locations before alignment into coherent chains. Our results indicate that no single factor alone is essential for MM formation, which instead is orchestrated by the cumulative action of several magnetosome proteins. One of the most intriguing examples for membrane-bounded prokaryotic organelles are magnetosomes which consist of well-ordered chains of perfectly shaped magnetic nanocrystals that in many aquatic bacteria serve as geomagnetic field sensors to direct their swimming towards microoxic zones at the bottom of natural waters. In the model bacterium Magnetospirillum gryphiswaldense and related magnetotactic microorganisms, magnetosomes are formed by a complex pathway that is orchestrated by more than 30 genes. However, the initial and most crucial step of magnetosome biosynthesis, formation and differentiation of a dedicated intracellular membrane compartment for controlled biomineralization of magnetite crystals, remained only poorly understood. By ultrastructural analysis of several mutants and genetic induction of de novo magnetosome synthesis, we identified the key determinants and early steps of magnetosome membrane biogenesis. Our results suggest that formation of intracellular membranes in bacteria is mediated by a cumulative action of several factors, but apparently is differently controlled than intracellular membrane remodeling in eukaryotic cells.