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首页> 外文期刊>Applied Microbiology >Overproduction of Magnetosomes by Genomic Amplification of Biosynthesis-Related Gene Clusters in a Magnetotactic Bacterium
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Overproduction of Magnetosomes by Genomic Amplification of Biosynthesis-Related Gene Clusters in a Magnetotactic Bacterium

机译：磁趋化细菌中生物合成相关基因簇的基因组扩增对磁小体的过量生产。

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摘要

Magnetotactic bacteria biosynthesize specific organelles, the magnetosomes, which are membrane-enclosed crystals of a magnetic iron mineral that are aligned in a linear chain. The number and size of magnetosome particles have to be critically controlled to build a sensor sufficiently strong to ensure the efficient alignment of cells within Earth's weak magnetic field while at the same time minimizing the metabolic costs imposed by excessive magnetosome biosynthesis. Apart from their biological function, bacterial magnetosomes have gained considerable interest since they provide a highly useful model for prokaryotic organelle formation and represent biogenic magnetic nanoparticles with exceptional properties. However, potential applications have been hampered by the difficult cultivation of these fastidious bacteria and their poor yields of magnetosomes. In this study, we found that the size and number of magnetosomes within the cell are controlled by many different Mam and Mms proteins. We present a strategy for the overexpression of magnetosome biosynthesis genes in the alphaproteobacterium Magnetospirillum gryphiswaldense by chromosomal multiplication of individual and multiple magnetosome gene clusters via transposition. While stepwise amplification of the mms6 operon resulted in the formation of increasingly larger crystals (increase of ～35%), the duplication of all major magnetosome operons ( mamGFDC , mamAB , mms6 , and mamXY , comprising 29 genes in total) yielded an overproducing strain in which magnetosome numbers were 2.2-fold increased. We demonstrate that the tuned expression of the mam and mms clusters provides a powerful strategy for the control of magnetosome size and number, thereby setting the stage for high-yield production of tailored magnetic nanoparticles by synthetic biology approaches.IMPORTANCE Before our study, it had remained unknown how the upper sizes and numbers of magnetosomes are genetically regulated, and overproduction of magnetosome biosynthesis had not been achieved, owing to the difficulties of large-scale genome engineering in the recalcitrant magnetotactic bacteria. In this study, we established and systematically explored a strategy for the overexpression of magnetosome biosynthesis genes by genomic amplification of single and multiple magnetosome gene clusters via sequential chromosomal insertion by transposition. Our findings also indicate that the expression levels of magnetosome proteins together limit the upper size and number of magnetosomes within the cell. We demonstrate that tuned overexpression of magnetosome gene clusters provides a powerful strategy for the precise control of magnetosome size and number.
机译：趋磁细菌生物合成特定的细胞器，即磁小体，它们是磁性铁矿物质的膜包裹晶体，排列成线性链。必须严格控制磁小体颗粒的数量和大小，以建立足够坚固的传感器，以确保地球弱磁场内细胞的有效排列，同时最大程度地减少由于过多的磁小体生物合成而产生的代谢成本。除了它们的生物学功能外，细菌磁小体还引起了极大的兴趣，因为它们为原核细胞器的形成提供了非常有用的模型，并代表了具有卓越性能的生物磁性纳米粒子。但是，由于难以培养这些营养细菌以及它们的磁小体产量低，阻碍了潜在的应用。在这项研究中，我们发现细胞内磁小体的大小和数量受许多不同的Mam和Mms蛋白控制。我们提出了通过单个和多个磁小体基因簇通过转座染色体倍增的alphaproteobacter Magnetospirillum gryphiswaldense中的磁小体生物合成基因的过表达策略。虽然逐步放大mms6操纵子导致形成越来越大的晶体（增加约35％），但所有主要磁小体操纵子（mamGFDC，mamAB，mms6和mamXY，总共包含29个基因）的重复产生了高产菌株其中磁小体数目增加了2.2倍。我们证明了mam和mms簇的调节表达为控制磁小体的大小和数量提供了强有力的策略，从而为通过合成生物学方法高产量生产定制的磁性纳米颗粒奠定了基础。尚不清楚如何通过遗传调控磁小体的上部大小和数量，并且由于顽固的趋磁细菌难以进行大规模的基因组工程，因此尚未实现磁小体生物合成的过量生产。在这项研究中，我们建立并系统地探索了通过单个染色体和多个磁小体基因簇的基因组扩增，通过转位顺序插入染色体来实现磁小体生物合成基因过表达的策略。我们的发现还表明，磁小体蛋白的表达水平共同限制了细胞内磁小体的上部大小和数量。我们证明，磁小体基因簇的调节过表达为精确控制磁小体的大小和数量提供了一种有力的策略。

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