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“Background Magnetotactic bacteria (MTB) use magnetosomes for orientation in the Earth’s magnetic field to search for click here growth-favoring oxygen-limited zones of stratified aquatic habitats [1]. In the freshwater alphaproteobacterium Magnetospirillum gryphiswaldense (in the following referred to as MSR-1) and other MTB, magnetosomes are membrane-enveloped magnetic crystals

of magnetite (Fe3O4) that are aligned in chains [1]. Magnetite biomineralization is not only controlled by more than 30 specific genes encoded within a genomic magnetosome island (MAI) [2–4], but also requires genes located outside MAI for synthesis of WT-like magnetosomes [5,

6]. Although the mechanism of biomineralization is not completely understood, it has been proposed that the biosynthesis of mixed-valence iron oxide magnetite [FeII(FeIII)2O4] occurs by coprecipitation of ferrous and ferric iron in supersaturating concentrations, which requires a balanced ratio of ferrous and ferric iron [7–9]. In magnetospirilla, magnetosome formation is only induced at low oxygen tension, and maximum magnetosome yield was found under microaerobic conditions in the presence of nitrate, whereas aerobic conditions completely inhibit magnetite biomineralization [5, 10]. However, it is unknown whether this aerobic repression is controlled of by biological regulation, or alternatively, directly buy RAD001 caused by chemical oxidation of iron ions within the cells. In addition, our recent work indicated that magnetite biomineralization in MSR-1 is linked to denitrification

[5, 6]. Deletion of nap genes encoding a periplasmic nitrate reductase not only abolished anaerobic growth and delayed aerobic growth in both nitrate and ammonium medium, but also severely impaired magnetite biomineralization and resulted in biosynthesis of fewer, smaller and irregular crystals during denitrification and microaerobic respiration [5]. In addition, loss of the nitrite reductase gene nirS led to defective growth of cells, which synthesized fewer, smaller and irregular crystals during nitrate reduction [6]. Transcriptional gusA fusions revealed that expression of nap is upregulated by oxygen, whereas other denitrification genes including nirS, nor, and nosZ display the highest expression under microaerobic conditions in the presence of nitrate [5]. In many bacteria, changes in oxygen tension serve as an important environmental GKT137831 molecular weight signal to trigger adaptive changes between anaerobic and aerobic respiration. This has been well studied in Escherichia coli where oxygen deprivation induces the synthesis of a number of enzymes, particularly those carrying out anaerobic respiration [11–15].