Frequent Mutations within the Genomic Magnetosome Island of Magnetospirillum gryphiswaldense Are Mediated by RecA

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.