Biosynthesis of the Iron-Molybdenum Cofactor of Nitrogenase

Rubio, Luis M.; Ludden, Paul W.

doi:10.1146/annurev.micro.62.081307.162737

Cited by 373 publications

(308 citation statements)

References 88 publications

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“…Using these primers, M. chthonoplastes-dominated microbial mats seem to be low in cyanobacterial specific nifH genes. As described in the introduction, this observation, in combination with the failure to detect nitrogenase activity in pure cultures of M. chthonoplastes, led to the general assumption that this organism lacked the genes for dinitrogen fixation and, hence, lacked the ability to fix dinitrogen (Zehr et al, 1995;Steppe and Paerl, 2002;de Wit et al, 2005) Our results, however, show that all strains of M. chthonoplastes tested by us contained nifH, nifD and nifK, and the genome sequence of M. chthonoplastes PCC7420 shows that a complete nif-gene cluster is present (Rubio and Ludden, 2008). As M. chthonoplastes forms large bundles of filaments enclosed in a thick extracellular polysaccharide sheath, it was difficult to grow this organism axenically.…”

Section: Discussionmentioning

confidence: 74%

“…In addition, the nifcluster contains two genes proposed to be involved in nitrogen regulation, P-II and P-II', (Martin and Reinhold-Hurek, 2002) and a gene encoding a ferredoxin protein (fd) mediating electron transfer (Rubio and Ludden, 2008). Two copies of nifB were found, of which the first seems to be a partial and possibly non-functional gene (nifB').…”

Section: Genetic Analysismentioning

confidence: 99%

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Horizontal transfer of the nitrogen fixation gene cluster in the cyanobacterium Microcoleus chthonoplastes

et al. 2009

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The filamentous, non-heterocystous cyanobacterium Microcoleus chthonoplastes is a cosmopolitan organism, known to build microbial mats in a variety of different environments. Although most of these cyanobacterial mats are known for their capacity to fix dinitrogen, M. chthonoplastes has not been assigned as a diazotrophic organism. None of the strains that were correctly identified as M. chthonoplastes has been shown to fix dinitrogen and it has repeatedly been reported that these organisms lacked the cyanobacterial nifH, the structural gene for dinitrogenase reductase. In this study, we show that a complete nif-gene cluster is present in the genome of M. chthonoplastes PCC 7420 and that the three structural nitrogenase genes, nifHDK, are present in a collection of axenic strains of M. chthonoplastes from distant locations. Phylogenetic analysis of nifHDK revealed that they cluster with the Deltaproteobacteria and that they are closely related to Desulfovibrio. The nif operon is flanked by typical cyanobacterial genes, suggesting that it is an integral part of the M. chthonoplastes genome. In this study, we provide evidence that the nif operon of M. chthonoplastes is acquired through horizontal gene transfer. Moreover, the presence of the same nif-cluster in M. chthonoplastes isolates derived from various sites around the world suggests that this horizontal gene transfer event must have occurred early in the evolution of M. chthonoplastes. We have been unable to express nitrogenase in cultures of M. chthonoplastes, but we show that these genes were expressed under natural conditions in the field.

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Section: Discussionmentioning

confidence: 74%

Section: Genetic Analysismentioning

confidence: 99%

Horizontal transfer of the nitrogen fixation gene cluster in the cyanobacterium Microcoleus chthonoplastes

et al. 2009

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“…This has been well illustrated in the case of the assembly of [FeS] clusters [11,12] or in the case of the maturation of nitrogenase [13].…”

Section: Introductionmentioning

confidence: 82%

The role of the maturase HydG in [FeFe]‐hydrogenase active site synthesis and assembly

et al. 2009

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a b s t r a c t[FeFe]-hydrogenases catalyze the protons/hydrogen interconversion through a unique di-iron active site consisting of three CO and two CN ligands, and a non-protein SCH 2 XCH 2 S (X = N or O) dithiolate bridge. Site assembly requires two ''Radical-S-adenosylmethionine (SAM or AdoMet)" iron-sulfur enzymes, HydE and HydG, and one GTPase, HydF. The sequence homology between HydG and ThiH, a Radical-SAM enzyme which cleaves tyrosine into p-cresol and dehydroglycine, and the finding of a similar cleavage reaction catalyzed by HydG suggests a mechanism for hydrogenase maturation. Here we propose that HydG is specifically involved in the synthesis of the dithiolate ligand, with two tyrosine-derived dehydroglycines as precursors along with an [FeS] cluster of HydG functioning both as electron shuttle and source of the sulfur atoms.

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“…Whereas much of the primary productivity in the tropical and subtropical regions of the oceans is predicted to be nitrogen limited, the diazotrophs' nitrogen source, resupplied from the large atmospheric reservoir, is essentially limitless. Instead, iron is considered the critical micronutrient for marine diazotrophs due to their use of the ironnitrogenase protein complex containing a homodimeric iron protein with a 4Fe∶4S metallocluster (NifH) and a heterotetrameric molybdenum-iron protein with an 8Fe∶7S P cluster and a 7 Fe and 1 Mo MoFe cofactor (NifDK, α and β subunits) (7,8) (Table S1). Field experiments and models both predict the distribution of oceanic nitrogen fixation to be primarily constrained by the availability of iron (2,(9)(10)(11).…”

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confidence: 99%

Iron conservation by reduction of metalloenzyme inventories in the marine diazotroph Crocosphaera watsonii

Saito¹,

Bertrand²,

Dutkiewicz

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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The marine nitrogen fixing microorganisms (diazotrophs) are a major source of nitrogen to open ocean ecosystems and are predicted to be limited by iron in most marine environments. Here we use global and targeted proteomic analyses on a key unicellular marine diazotroph Crocosphaera watsonii to reveal large scale diel changes in its proteome, including substantial variations in concentrations of iron metalloproteins involved in nitrogen fixation and photosynthesis, as well as nocturnal flavodoxin production. The daily synthesis and degradation of enzymes in coordination with their utilization results in a lowered cellular metalloenzyme inventory that requires ∼40% less iron than if these enzymes were maintained throughout the diel cycle. This strategy is energetically expensive, but appears to serve as an important adaptation for confronting the iron scarcity of the open oceans. A global numerical model of ocean circulation, biogeochemistry and ecosystems suggests that Crocosphaera's ability to reduce its iron-metalloenzyme inventory provides two advantages: It allows Crocosphaera to inhabit regions lower in iron and allows the same iron supply to support higher Crocosphaera biomass and nitrogen fixation than if they did not have this reduced iron requirement.cyanobacteria | marine iron cycle | nitrogen cycle

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Biosynthesis of the Iron-Molybdenum Cofactor of Nitrogenase

Cited by 373 publications

References 88 publications

Horizontal transfer of the nitrogen fixation gene cluster in the cyanobacterium Microcoleus chthonoplastes

Horizontal transfer of the nitrogen fixation gene cluster in the cyanobacterium Microcoleus chthonoplastes

The role of the maturase HydG in [FeFe]‐hydrogenase active site synthesis and assembly

Iron conservation by reduction of metalloenzyme inventories in the marine diazotroph Crocosphaera watsonii

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