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Applied and Environmental Microbiology, September 2006, p. 5757-5765, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.00201-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Transcriptional Organization and Regulation of Magnetosome Operons in Magnetospirillum gryphiswaldense

Max Planck Institute for Marine Microbiology, Department of Microbiology, Celsiusstr. 1, 28359 Bremen, Germany,¹ Max Planck Institute for Marine Microbiology, Microbial Genomics Group, Celsiusstr. 1, 28359 Bremen, Germany²

Received 25 January 2006/ Accepted 16 June 2006

Genes involved in magnetite biomineralization are clustered within the genomic magnetosome island of Magnetospirillum gryphiswaldense. Their transcriptional organization and regulation were studied by several approaches. Cotranscription of genes within the mamAB, mamDC, and mms clusters was demonstrated by reverse transcription-PCR (RT-PCR) of intergenic regions, indicating the presence of long polycistronic transcripts extending over more than 16 kb. The transcription start points of the mamAB, mamDC, and mms operons were mapped at 22 bp, 52 bp, and 58 bp upstream of the first genes of the operons, respectively. Identified –10 and –35 boxes of the P_mamAB, P_mamDC, and P_mms promoters showed high similarity to the canonical ⁷⁰ recognition sequence. The transcription of magnetosome genes was further studied in response to iron and oxygen. Transcripts of magnetosome genes were detected by RT-PCR both in magnetic cells grown microaerobically under iron-sufficient conditions and in nonmagnetic cells grown either aerobically or with iron limitation. The presence of transcripts was found to be independent of the growth phase. Further results from partial RNA microarrays targeting the putative magnetosome transcriptome of M. gryphiswaldense and real-time RT-PCR experiments indicated differences in expression levels depending on growth conditions. The expression of the mam and mms genes was down-regulated in nonmagnetic cells under iron limitation and, to a lesser extent, during aerobic growth compared to that in magnetite-forming cells grown microaerobically under iron-sufficient conditions.

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