[52] Electron donation to nitrogenase in heterocysts

Bothe, Hermann; Neuer, G.

doi:10.1016/0076-6879(88)67055-8

Cited by 24 publications

(21 citation statements)

References 20 publications

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“…We cannot, however, explain why dithionite did not support proportionally higher acetylene reducing activity follow- (Fig. 1) and then to ␣-ketoglutarate, which would yield reduced ferredoxin and NADPH (5,34). We found no molecular genetic evidence for a second zwf gene in addition to that in the opc operon and have no facile explanation for the low level of G6P-dependent NADPH production in extracts of zwf mutant strain UCD 341.…”

Section: Discussioncontrasting

confidence: 45%

“…The reduction of N 2 to NH 3 by nitrogenase requires the molar equivalent of at least eight electrons and 16 ATP molecules (55). Studies describing enzyme activities and substrates capable of supporting nitrogenase activity in heterocyst extracts implicated either the initial enzymes of the oxidative pentose phosphate (OPP) pathway or those of the Embden-Meyerhof-Parnas, or glycolytic, pathway as the source(s) of reductant required for conversion of N 2 to NH 3 and for respiratory O 2 uptake (1,5,33,53), with vegetative cells supplying the reduced carbon substrate (54). However, there have been neither genetic nor detailed radiotracer experiments to resolve the routes of carbon catabolism in heterocysts.…”

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confidence: 99%

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Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133

et al. 1995

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Heterocysts, sites of nitrogen fixation in certain filamentous cyanobacteria, are limited to a heterotrophic metabolism, rather than the photoautotrophic metabolism characteristic of cyanobacterial vegetative cells. The metabolic route of carbon catabolism in the supply of reductant to nitrogenase and for respiratory electron transport in heterocysts is unresolved. The gene (zwf) encoding glucose-6-phosphate dehydrogenase (G6PD), the initial enzyme of the oxidative pentose phosphate pathway, was inactivated in the heterocyst-forming, facultatively heterotrophic cyanobacterium, Nostoc sp. strain ATCC 29133. The zwf mutant strain had less than 5% of the wild-type apparent G6PD activity, while retaining wild-type rates of photoautotrophic growth with NH 4 ؉ and of dark O 2 uptake, but it failed to grow either under N 2 -fixing conditions or in the dark with organic carbon sources. A wild-type copy of zwf in trans in the zwf mutant strain restored only 25% of the G6PD specific activity, but the defective N 2 fixation and dark growth phenotypes were nearly completely complemented. Transcript analysis established that zwf is in an operon also containing genes encoding two other enzymes of the oxidative pentose phosphate cycle, fructose-1,6-bisphosphatase and transaldolase, as well as a previously undescribed gene (designated opcA) that is cotranscribed with zwf. Inactivation of opcA yielded a growth phenotype identical to that of the zwf mutant, including a 98% decrease, relative to the wild type, in apparent G6PD specific activity. The growth phenotype and lesion in G6PD activity in the opcA mutant were complemented in trans with a wild-type copy of opcA. In addition, placement in trans of a multicopy plasmid containing the wild-type copies of both zwf and opcA in the zwf mutant resulted in an approximately 20-fold stimulation of G6PD activity, relative to the wild type, complete restoration of nitrogenase activity, and a slight stimulation of N 2 -dependent photoautotrophic growth and fructose-supported dark growth. These results unequivocally establish that G6PD, and most likely the oxidative pentose phosphate pathway, represents the essential catabolic route for providing reductant for nitrogen fixation and respiration in differentiated heterocysts and for dark growth of vegetative cells. Moreover, the opcA gene product is involved by an as yet unknown mechanism in G6PD synthesis or catalytic activity.Cyanobacteria are a morphologically diverse but phylogenetically cohesive group of gram-negative eubacteria that are phenotypically united by their oxygen-evolving photosynthetic mechanism. All cyanobacteria are photoautotrophic, using ATP and NADPH generated in the light reactions for autotrophic CO 2 assimilation by enzymes of the Calvin-Benson, or reductive pentose phosphate, cycle. They synthesize glycogen as the storage material in the light, and this glycogen is subsequently catabolized to provide maintenance energy during the dark periods of natural day-night cycles.The vegetative cells of many filamentous cya...

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Section: Discussioncontrasting

confidence: 45%

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confidence: 99%

Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133

et al. 1995

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“…In contrast, G6PD protein levels in Nostoc symbionts are up-shifted under the dark heterotrophic conditions offered in plant symbiosis (Ekman et al, 2006). This result is expected since the OPP pathway is a major route for providing reductants (NADPH) to nitrogenase in heterocysts (Winkenbach & Wolk, 1973;Bothe & Neuer 1988). This illustrates the metabolic flexibility of the genus and the findings are supported by our data.…”

Section: Discussionsupporting

confidence: 82%

Proteomic analyses of the photoauto- and diazotrophically grown cyanobacterium Nostoc sp. PCC 73102

et al. 2007

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The filamentous cyanobacteria of the genus Nostoc are globally distributed, phenotypically complex organisms, capable of cellular differentiation and of forming symbiotic associations with a wide range of plants. To further our understanding of these processes and functions, the proteome of photoautotrophically and diazotrophically grown Nostoc sp. PCC 73102 (N. punctiforme) cells was examined. Extracted proteins were separated into membrane and soluble protein fractions and analysed using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The analysis led to the identification of 82 proteins that could be divided into 12 functional categories. Significantly, 65 of these proteins have not been previously documented in the Nostoc proteome. Many of the proteins identified were readily recognized as housekeeping proteins involved in carbon, nitrogen and energy metabolism, but a number of proteins related to stress, motility, secretion and post-translational modifications were also identified. Ten unclassified proteins were also detected, representing potential novel functions. These proteins were highly expressed, suggesting that they play key roles during photoautotrophic and diazotrophic growth. Nineteen of the proteins expressed under the growth conditions examined contained putative thioredoxin (Trx) targets, a motif that functions in redox regulation via redox equivalent mediators and is known to be significant in a wide range of biological processes. These observations contribute to our understanding of the complex Nostoc life cycle.

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“…Generally, intact N 2 -fixing cyanobacteria show very little net H 2 production due to the efficient recycling of the gas by uptake hydrogenase. This H 2 consumption proceeds by the respiration-and photosystem I-dependent pathways (33). In cyanobacteria, respiration and photosynthesis share the cytochrome bc complex (respiratory complex III), from where the electrons are allocated either to the donor side of photosystem I to generate reduced ferredoxin or to respiratory complex IV accompanied by O 2 consumption.…”

Section: Hydrogenases In Cyanobacteria Hydrogenase Types In Cyanobactmentioning

confidence: 99%

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

Bothe

Schmitz²,

Yates

et al. 2010

Microbiol Mol Biol Rev

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357

222

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SUMMARY This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N2 fixation and/or H2 formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H2 as a source of combustible energy. To enhance the rates of H2 production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H2 formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.

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[52] Electron donation to nitrogenase in heterocysts

Cited by 24 publications

References 20 publications

Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133

Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133

Proteomic analyses of the photoauto- and diazotrophically grown cyanobacterium Nostoc sp. PCC 73102

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

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