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Characterization Of A Spontaneous Nonmagnetic Mutant Of Magnetospirillum Gryphiswaldense Reveals A Large Deletion Comprising A Putative Magnetosome Island

Sabrina Schübbe, Michael Kube, André Scheffel, Cathrin Wawer, Udo Heyen, Anke Meyerdierks, Mohamed H. Madkour, Frank Mayer, Richard Reinhardt, Dirk Schüler

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ABSTRACT Frequent spontaneous loss of the magnetic phenotype was observed in stationary-phase cultures of the magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1. A nonmagnetic mutant, designated strain MSR-1B, was isolated and characterized. The mutant lacked any structures resembling magnetosome crystals as well as internal membrane vesicles. The growth of strain MSR-1B was impaired under all growth conditions tested, and the uptake and accumulation of iron were drastically reduced under iron-replete conditions. A large chromosomal deletion of approximately 80 kb was identified in strain MSR-1B, which comprised both the entire mamAB and mamDC clusters as well as further putative operons encoding a number of magnetosome-associated proteins. A bacterial artificial chromosome clone partially covering the deleted region was isolated from the genomic library of wild-type M. gryphiswaldense. Sequence analysis of this fragment revealed that all previously identified mam genes were closely linked with genes encoding other magnetosome-associated proteins within less than 35 kb. In addition, this region was remarkably rich in insertion elements and harbored a considerable number of unknown gene families which appeared to be specific for magnetotactic bacteria. Overall, these findings suggest the existence of a putative large magnetosome island in M. gryphiswaldense and other magnetotactic bacteria.