The rnf gene products in Rhodobacter capsulatus play an essential role in nitrogen fixation during anaerobic DMSO-dependent growth in the dark

Saeki, Kazuhiko; Kumagai, Hirotaka

doi:10.1007/s002030050598

Cited by 36 publications

(28 citation statements)

References 3 publications

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“…The Rnf complex was first described in Rhodobacter capsulatus (34), where it is proposed to encode a six-subunit (20) membrane-bound complex (RnfABCDGE) oxidizing NADH and reducing a ferredoxin which then donates electrons to nitrogenase (23,34). It is further proposed that the thermodynamically unfavorable reverse electron transport is driven by an electrochemical gradient (27,33). It has previously been suggested (23) that the Rnf complex is a new energy-coupling family that may also function to generate an electrochemical gradient for ATP synthesis, consistent with the proposed function in M. acetivorans.…”

Section: Resultsmentioning

confidence: 99%

Electron Transport in the Pathway of Acetate Conversion to Methane in the Marine Archaeon Methanosarcina acetivorans

et al. 2006

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Section: Resultsmentioning

confidence: 99%

Electron Transport in the Pathway of Acetate Conversion to Methane in the Marine Archaeon Methanosarcina acetivorans

et al. 2006

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“…rubrum and Rd. capsulatus can also perform anaerobic photolithoautotrophy (479,550), anaerobic photoheterotrophy (35), nitrate respiration (451), dimethyl sulfoxide respiration (425), or growth on carbon monoxide (239), to name a few of the possibilities, in addition to being able to fix nitrogen in the light or in the dark (425), if needed.…”

Section: Comparing Diversity: Eukaryotes Versus Rhodobactermentioning

confidence: 99%

Biochemistry and Evolution of Anaerobic Energy Metabolism in Eukaryotes

Müller

Mentel

Hellemond

et al. 2012

Microbiol Mol Biol Rev

685

904

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SUMMARY Major insights into the phylogenetic distribution, biochemistry, and evolutionary significance of organelles involved in ATP synthesis (energy metabolism) in eukaryotes that thrive in anaerobic environments for all or part of their life cycles have accrued in recent years. All known eukaryotic groups possess an organelle of mitochondrial origin, mapping the origin of mitochondria to the eukaryotic common ancestor, and genome sequence data are rapidly accumulating for eukaryotes that possess anaerobic mitochondria, hydrogenosomes, or mitosomes. Here we review the available biochemical data on the enzymes and pathways that eukaryotes use in anaerobic energy metabolism and summarize the metabolic end products that they generate in their anaerobic habitats, focusing on the biochemical roles that their mitochondria play in anaerobic ATP synthesis. We present metabolic maps of compartmentalized energy metabolism for 16 well-studied species. There are currently no enzymes of core anaerobic energy metabolism that are specific to any of the six eukaryotic supergroup lineages; genes present in one supergroup are also found in at least one other supergroup. The gene distribution across lineages thus reflects the presence of anaerobic energy metabolism in the eukaryote common ancestor and differential loss during the specialization of some lineages to oxic niches, just as oxphos capabilities have been differentially lost in specialization to anoxic niches and the parasitic life-style. Some facultative anaerobes have retained both aerobic and anaerobic pathways. Diversified eukaryotic lineages have retained the same enzymes of anaerobic ATP synthesis, in line with geochemical data indicating low environmental oxygen levels while eukaryotes arose and diversified.

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“…As shown above, clostridia and other anaerobes have no problem with providing these agents, but nitrogen-fixing aerobes and phototrophs do have difficulties. One solution is Rnf from R. capsulatus, which is thought to catalyze the NADH-dependent reduction of ferredoxin driven by ⌬H ϩ (36,38). Rhodospirillum rubrum, however, lacks the rnfABCDFG genes, but it contains the fixABCX cluster that is also present in several other diazotrophic bacteria (11)(12)(13).…”

Section: Nitrogen Fixationmentioning

confidence: 99%

Energy Conservation via Electron-Transferring Flavoprotein in Anaerobic Bacteria

et al. 2008

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Energy conservation in chemotrophic organisms is generally coupled to redox reactions in catabolic pathways. In the oxidative part or branch, "energy-rich" compounds are formed, from which ATP is generated via substrate-level phosphorylation (SLP). In the reductive branch the electron carriers are reoxidized by a terminal acceptor; in this way an electrochemical ion gradient (⌬H ϩ or ⌬Na ϩ ) at the cytoplasmic membrane is established, which is used for ATP synthesis, transport across membranes, and motility. This second type of energy conservation is called respiration or electron transport phosphorylation (ETP). Bacterial fermentations are considered apparent exceptions to this generalization because they are thought to lack ETP (41). In these fermentations the substrate serves not only as an electron donor but also as a terminal acceptor, since oxygen, nitrate, fumarate, etc. are absent (44). An example is the fermentation of glutamate via 3-methylasparate by the closely related anaerobic bacteria Clostridium tetani, Clostridium tetanomorphum, and Clostridium pascui to ammonia, acetate, butyrate, and molecular hydrogen according to equation 1 (Fig. 1) (8,16,51):In the first part of this pathway, glutamate is converted to ammonia, acetate, and pyruvate, which is oxidized by ferredoxin and coenzyme A (CoA) to acetyl-CoA and CO 2 . In order to regenerate the oxidant, acetyl-CoA and protons are reduced to butyryl-CoA and hydrogen, respectively. From 2 butyrylCoA and 1 acetyl-CoA, 3 ATP are obtained via SLP. But the free enthalpy required to synthesize 1 ATP (Ϫ317/3 ϭ Ϫ106 kJ mol Ϫ1 ) is still much higher than that needed in other systems; i.e., the efficiency is low ( ϭ 42%). Usually, Ϫ75 Ϯ 5 kJ mol Ϫ1 ( ϭ 60%) is considered the minimum free enthalpy for ATP synthesis (44). It should be noted that without hydrogen formation the ATP yield would drop to 2.5 mol ATP (5 mol glutamate)Ϫ1 , because in order to maintain the redox balance, acetyl-CoA has to be completely reduced to butyrate. Thus, hydrogen formation increases SLP. If all the reducing equivalents dissipated as hydrogen and no butyrate was formed, the yield would rise to 5 mol ATP (5 mol glutamate)Ϫ1 . This, however, is thermodynamically not possible (Ϫ46 kJ mol glutamate Ϫ1 ). The oxidation of pyruvate derived from glutamate yields reduced ferredoxin (E 0 Ј Յ Ϫ420 mV), whereas NADH (E 0 Ј ϭ Ϫ320 mV) is the reductant in butyrate synthesis. The difference (Ն100 mV) could be used for additional energy conservation. Recently, we discovered the enzyme that catalyzes the reduction of NAD ϩ with reduced ferredoxin (Fig. 1) and characterized it as an Rnf-type NADH ferredoxin oxidoreductase localized in the membrane of C. tetanomorphum. Although it has not been demonstrated yet that this clostridial Rnf protein pumps protons or sodium ions, its cellular localization and the homology of four of its six subunits with four of the subunits of NADH-quinone reductase (Nqr) from Vibrio alginolyticus and Vibrio cholerae strongly suggest that this enzyme is involved in ener...

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The rnf gene products in Rhodobacter capsulatus play an essential role in nitrogen fixation during anaerobic DMSO-dependent growth in the dark

Cited by 36 publications

References 3 publications

Electron Transport in the Pathway of Acetate Conversion to Methane in the Marine Archaeon Methanosarcina acetivorans

Electron Transport in the Pathway of Acetate Conversion to Methane in the Marine Archaeon Methanosarcina acetivorans

Biochemistry and Evolution of Anaerobic Energy Metabolism in Eukaryotes

Energy Conservation via Electron-Transferring Flavoprotein in Anaerobic Bacteria

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