Ludwig-Maximilians-Universität München, Department Biologie I, Bereich Mikrobiologie, Biozentrum der LMU, Großhaderner Str. 4, 82152 Planegg-Martinsried, Germany.
J Bacteriol. 2011 Oct;193(19):5328-34. doi: 10.1128/JB.05491-11. Epub 2011 Aug 5.
Genes for magnetosome formation in magnetotactic bacteria are clustered in large genomic magnetosome islands (MAI). Spontaneous deletions and rearrangements were frequently observed within these regions upon metabolic stress. This instability was speculated to be due to RecA-dependent homologous recombination between the numerous sequence repeats present within the MAI. Here we show that a RecA-deficient strain of Magnetospirillum gryphiswaldense (IK-1) no longer exhibits genetic instability of magnetosome formation. Strain IK-1 displayed higher sensitivity to oxygen and UV irradiation. Furthermore, the lack of RecA abolished allelic exchange in the mutant. Cells of strain IK-1 displayed a slightly altered (i.e., more elongated) morphology, whereas the absence of RecA did not affect the ability to synthesize wild-type-like magnetosomes. Our data provide evidence that the observed genetic instability of magnetosome formation in the wild type is due predominantly to RecA-mediated recombination. In addition, increased genetic stability could make strain IK-1 a useful tool for the expression of genes and further genetic engineering, as well as for biotechnological production of bacterial magnetosomes.
在趋磁细菌中，用于磁小体形成的基因簇集在大型基因组磁小体岛（MAI）中。在代谢应激下，这些区域内经常观察到自发缺失和重排。这种不稳定性被推测是由于 MAIs 中存在的大量序列重复之间依赖 RecA 的同源重组所致。在这里，我们表明，缺乏 RecA 的趋磁螺菌（IK-1）菌株不再表现出磁小体形成的遗传不稳定性。菌株 IK-1 对氧和紫外线照射的敏感性更高。此外，RecA 的缺失消除了突变体中的等位基因交换。菌株 IK-1 的细胞显示出略微改变的（即更长的）形态，而 RecA 的缺失并不影响合成类似野生型磁小体的能力。我们的数据提供了证据，表明野生型中观察到的磁小体形成的遗传不稳定性主要是由于 RecA 介导的重组。此外，增加遗传稳定性可以使菌株 IK-1 成为表达基因和进一步遗传工程以及细菌磁小体生物技术生产的有用工具。
