Genetic Dissection of the mamAB and mms6 Operons Reveals a Gene Set Essential for Magnetosome Biogenesis in Magnetospirillum gryphiswaldense
Genetic Dissection of the mamAB and mms6 Operons Reveals a Gene Set Essential for Magnetosome Biogenesis in Magnetospirillum gryphiswaldense
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DOI：
10.1128/jb.01716-14
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发表时间：
2014-07-01
影响因子：
3.2
通讯作者：
Schueler, Dirk
中科院分区：
文献类型：
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作者：
Lohsse, Anna;Borg, Sarah;Schueler, Dirk
细菌磁小体是细胞内膜封闭的纳米级磁性晶体，其生物合成由一组> 30个特定基因控制。在磁小体中，这些主要聚集在包含mms 6、mamGFDC、mamAB和mamXY操纵子的大的保守基因组磁小体岛（MAI）内。在这里，我们证明了5个以前未表征的基因的mms 6操纵子有至关重要的功能，磁小体生物矿化的调节，部分重叠MamF和其他蛋白质编码的相邻的mamGFDC操纵子。虽然所有其他缺失导致尺寸减小，但mms 36或mms 48的消除导致比野生型（WT）中的那些更大的磁铁矿晶体的合成。而MMS 6操纵子编码晶体成熟的辅助因子，大的mamAB操纵子包含几个必需和非必需的基因参与磁小体生物合成的各种其他步骤，如所有mamAB基因的单缺失所示。而mamL、-P、-Q、-R、-B、-S、-T和-U的单缺失表现出与先前在相关的M中研究的其直系同源物相似的表型。magneticum，我们发现mamI和mamN是不需要的，至少在M. gryphiswaldense。因此，只有mamE，-L，-M，-O，-Q，和-B是必不可少的磁铁矿的形成，而mamI突变体仍然生物矿化的微小颗粒，然而，由铁氧化物赤铁矿，如高分辨率透射电子显微镜（HRTEM）和X射线吸收近边结构（XANES）所示。在此基础上，我们提出了一个扩展的磁小体生物合成模型。gryphiswaldense。
Biosynthesis of bacterial magnetosomes, which are intracellular membrane-enclosed, nanosized magnetic crystals, is controlled by a set of > 30 specific genes. In Magnetospirillum gryphiswaldense, these are clustered mostly within a large conserved genomic magnetosome island (MAI) comprising the mms6, mamGFDC, mamAB, and mamXY operons. Here, we demonstrate that the five previously uncharacterized genes of the mms6 operon have crucial functions in the regulation of magnetosome biomineralization that partially overlap MamF and other proteins encoded by the adjacent mamGFDC operon. While all other deletions resulted in size reduction, elimination of either mms36 or mms48 caused the synthesis of magnetite crystals larger than those in the wild type (WT). Whereas the mms6 operon encodes accessory factors for crystal maturation, the large mamAB operon contains several essential and nonessential genes involved in various other steps of magnetosome biosynthesis, as shown by single deletions of all mamAB genes. While single deletions of mamL, -P, -Q, -R, -B, -S, -T, and -U showed phenotypes similar to those of their orthologs in a previous study in the related M. magneticum, we found mamI and mamN to be not required for at least rudimentary iron biomineralization in M. gryphiswaldense. Thus, only mamE, -L, -M, -O, -Q, and -B were essential for formation of magnetite, whereas a mamI mutant still biomineralized tiny particles which, however, consisted of the nonmagnetic iron oxide hematite, as shown by high-resolution transmission electron microscopy (HRTEM) and the X-ray absorption near-edge structure (XANES). Based on this and previous studies, we propose an extended model for magnetosome biosynthesis in M. gryphiswaldense.