Abstract
Magnetospirillum gryphiswaldense strain MSR-1 has the unique capability of taking up large amounts of iron and synthesizing magnetosomes (intracellular magnetic particles composed of Fe3O4). The unusual high iron content of MSR-1 makes it a useful model for studying biological mechanisms of iron uptake and homeostasis. The ferric uptake regulator (Fur) protein plays a key role in maintaining iron homeostasis in many bacteria. We identified and characterized a fur-homologous gene (MGR_1314) in MSR-1. MGR_1314 was able to complement a fur mutant of E. coli in iron-responsive manner in vivo. We constructed a fur mutant strain of MSR-1. In comparison to wild-type MSR-1, the mutant strain had lower magnetosome formation, and was more sensitive to hydrogen peroxide and streptonigrin, indicating higher intracellular free iron content. Quantitative real-time RT-PCR and chromatin immunoprecipitation analyses indicated that Fur protein directly regulates expression of several key genes involved in iron transport and oxygen metabolism, in addition it also functions in magnetosome formation in M. gryphiswaldense.
Highlights
Iron is an essential microelement for bacteria, being an important cofactor for a wide range of cellular processes, e.g., nitrogen fixation, photosynthesis, H2 production and consumption, membrane energetic, oxygen transport and DNA biosynthesis
Our results suggests that fur gene assists in magnetosome formation in MSR-1, that ferric uptake regulator (Fur) protein directly regulates expression of several genes involved in iron and oxygen metabolism
Examination of the genomic sequence of MSR-1 revealed the presence of four genes (MGR_1305, MGR_1314, MGR_1399, MGR_3480) having products characterized as belonging to the Fur protein family
Summary
Iron is an essential microelement for bacteria, being an important cofactor for a wide range of cellular processes, e.g., nitrogen fixation, photosynthesis, H2 production and consumption, membrane energetic, oxygen transport and DNA biosynthesis. Excessive uptake of iron may lead to oxidative damage via the Fenton reaction [2,3], so precise control of iron homeostasis is necessary. Fur (ferric uptake regulator) is the most common and best characterized transcriptional regulator of genes involved in iron uptake, storage and metabolism. When sufficient iron is present, Fur forms a complex with ferrous ions, and binds to a conserved 19 bp DNA sequence (‘‘Fur box’’) which overlaps the promoters and suppresses their transcription. Fur dissociates from the promoters, their transcription occurs and genes involved in the iron uptake system are expressed [4,5]
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