CEA Cadarache/CNRS/Aix-Marseille Université, UMR7265 Service de Biologie Végétale et de Microbiologie Environnementale, Laboratoire de Bioénergétique Cellulaire, 13108, Saint Paul lez Durance, France.
Environ Microbiol. 2013 Oct;15(10):2712-35. doi: 10.1111/1462-2920.12128. Epub 2013 Apr 23.
Magnetotactic bacteria (MTB) represent a group of diverse motile prokaryotes that biomineralize magnetosomes, the organelles responsible for magnetotaxis. Magnetosomes consist of intracellular, membrane-bounded, tens-of-nanometre-sized crystals of the magnetic minerals magnetite (Fe3O4) or greigite (Fe3S4) and are usually organized as a chain within the cell acting like a compass needle. Most information regarding the biomineralization processes involved in magnetosome formation comes from studies involving Alphaproteobacteria species which biomineralize cuboctahedral and elongated prismatic crystals of magnetite. Many magnetosome genes, the mam genes, identified in these organisms are conserved in all known MTB. Here we present a comparative genomic analysis of magnetotactic Deltaproteobacteria that synthesize bullet-shaped crystals of magnetite and/or greigite. We show that in addition to mam genes, there is a conserved set of genes, designated mad genes, specific to the magnetotactic Deltaproteobacteria, some also being present in Candidatus Magnetobacterium bavaricum of the Nitrospirae phylum, but absent in the magnetotactic Alphaproteobacteria. Our results suggest that the number of genes associated with magnetotaxis in magnetotactic Deltaproteobacteria is larger than previously thought. We also demonstrate that the minimum set of mam genes necessary for magnetosome formation in Magnetospirillum is also conserved in magnetite-producing, magnetotactic Deltaproteobacteria. Some putative novel functions of mad genes are discussed.
趋磁细菌（MTB）是一组多样化的能动原核生物，它们生物矿化磁小体，磁小体是负责趋磁作用的细胞器。磁小体由细胞内、膜结合的、数十纳米大小的磁性矿物磁铁矿（Fe3O4）或硫铁矿（Fe3S4）晶体组成，通常在细胞内组织成链状，类似于指南针的指针。关于磁小体形成过程中的生物矿化过程的大多数信息都来自于涉及 Alpha 变形菌的研究，这些菌生物矿化出立方体八面体和拉长的棱柱形磁铁矿晶体。在这些生物体中发现的许多磁小体基因，即 mam 基因，在所有已知的 MTB 中都是保守的。在这里，我们对合成磁铁矿和/或硫铁矿子弹形晶体的趋磁 Delta 变形菌进行了比较基因组分析。我们表明，除了 mam 基因外，还有一组保守的基因，称为 mad 基因，这些基因是趋磁 Delta 变形菌特有的，一些基因也存在于硝化螺旋菌门的 Candidatus Magnetobacterium bavaricum 中，但在趋磁 Alpha 变形菌中不存在。我们的结果表明，趋磁 Delta 变形菌中与趋磁作用相关的基因数量比之前认为的要多。我们还证明，在 Magnetospirillum 中形成磁小体所需的最小的 mam 基因集也在产磁铁矿的趋磁 Delta 变形菌中保守。讨论了一些假定的 mad 基因的新功能。
