title: Cytochrome cd1 nitrite reductase NirS is involved in anaerobic magnetite biomineralization in Magnetospirillum gryphiswaldense and requires NirN for proper d1 heme assembly.
abstract: The alphaproteobacterium Magnetospirillum gryphiswaldense synthesizes magnetosomes, which are membrane-enveloped crystals of magnetite. Here we show that nitrite reduction is involved in redox control during anaerobic biomineralization of the mixed-valence iron oxide magnetite. The cytochrome cd1-type nitrite reductase NirS shares conspicuous sequence similarity with NirN, which is also encoded within a larger nir cluster. Deletion of any one of these two nir genes resulted in impaired growth and smaller, fewer, and aberrantly shaped magnetite crystals during nitrate reduction. However, whereas nitrite reduction was completely abolished in the ΔnirS mutant, attenuated but significant nitrite reduction occurred in the ΔnirN mutant, indicating that only NirS is a nitrite reductase in M. gryphiswaldense. However, the ΔnirN mutant produced a different form of periplasmic d(1) heme that was not noncovalently bound to NirS, indicating that NirN is required for full reductase activity by maintaining a proper form of d1 heme for holo-cytochrome cd(1) assembly. In conclusion, we assign for the first time a physiological function to NirN and demonstrate that effective nitrite reduction is required for biomineralization of wild-type crystals, probably by contributing to oxidation of ferrous iron under oxygen-limited conditions.
authors.affiliation: Ludwig-Maximilians-Universität München, Department Biologie I, Mikrobiologie, Planegg-Martinsried, Germany.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Li
authors.forename: Shilpa
authors.initials: S
authors.lastname: Bali
authors.forename: Sarah
authors.initials: S
authors.lastname: Borg
authors.forename: Emanuel
authors.initials: E
authors.lastname: Katzmann
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Ferguson
authors.forename: Dirk
authors.initials: D
authors.lastname: Schüler
mesh_terms: D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003580:Cytochromes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D052203:Ferrosoferric Oxide / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives* / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D055944:Magnetosomes; D042201:Magnetospirillum / Q000145:classification / Q000201:enzymology*; D009572:Nitrite Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010084:Oxidation-Reduction
chemical_list: D001426:Bacterial Proteins; D003580:Cytochromes; D009573:Nitrites; D006418:Heme; C029400:heme d1; D007501:Iron; D009572:Nitrite Reductases; C028123:nitrite reductase (NO-forming); D052203:Ferrosoferric Oxide
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