Regulation of Hydrogenase Gene Expression

Vignais, Paulette M.; Toussaint, Bertrand; Colbeau, Annette

doi:10.1007/978-1-4020-8815-5_37

Cited by 11 publications

(4 citation statements)

References 88 publications

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“…In the absence of H 2 , HoxJ transfers phosphate to the transcriptional response regulator HoxA, which is inactive in the phosphorylated form. Biochemical and genetic data suggest that signal transduction between the regulatory [NiFe]-hydrogenase and HoxJ involves an electron transport process (80)(81)(82)(83)(84)(85)(86). The regulatory [NiFe]-hydrogenase contains an active site similar to that of the standard [NiFe]-hydrogenases.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen Formation and Its Regulation in Ruminococcus albus: Involvement of an Electron-Bifurcating [FeFe]-Hydrogenase, of a Non-Electron-Bifurcating [FeFe]-Hydrogenase, and of a Putative Hydrogen-Sensing [FeFe]-Hydrogenase

et al. 2014

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bRuminococcus albus 7 has played a key role in the development of the concept of interspecies hydrogen transfer. The rumen bacterium ferments glucose to 1.3 acetate, 0.7 ethanol, 2 CO 2 , and 2.6 H 2 when growing in batch culture and to 2 acetate, 2 CO 2 , and 4 H 2 when growing in continuous culture in syntrophic association with H 2 -consuming microorganisms that keep the H 2 partial pressure low. The organism uses NAD ؉ and ferredoxin for glucose oxidation to acetyl coenzyme A (acetyl-CoA) and CO 2 , NADH for the reduction of acetyl-CoA to ethanol, and NADH and reduced ferredoxin for the reduction of protons to H 2 . Of all the enzymes involved, only the enzyme catalyzing the formation of H 2 from NADH remained unknown. Here, we report that R. T he genus Ruminococcus (class Clostridia) consists of species of anaerobic, Gram-positive bacteria. One or more species of this genus are found in significant numbers in the intestines of humans (enterotype 3) (1, 2) and in the rumen and colon of herbivores (3, 4). Ruminococcus flavefaciens and Ruminococcus albus are among the most important plant cell wall-degrading bacteria in the rumen. These two species produce all required enzymes for hydrolyzing the plant cell wall polysaccharides, cellulose and hemicellulose (5, 6).R. albus was isolated in 1957 from the rumen of cattle by Hungate (7,8), who showed that in batch culture the bacterium ferments cellulose, cellobiose, or glucose to acetate, CO 2 , ethanol, and H 2 . Nevertheless, neither H 2 nor ethanol accumulate to high concentrations in the rumen (9, 10). The low H 2 concentrations in the rumen have been explained by the presence of H 2 -consuming microorganisms, such as Methanobrevibacter ruminantium (formerly Methanobacterium ruminantium), that consume H 2 more rapidly than it is formed from cellulose by R. albus (11). The laboratory of Bryant and Wolin then showed in 1973 that the fermentation of glucose by R. albus strain 7 was shifted from 1.3 acetic acid, 0.7 ethanol, 2 CO 2 , and 2.6 H 2 in batch culture to 2 acetic acid, 2 CO 2 , and 4 H 2 in chemostat culture together with Wolinella succinogenes (formerly Vibrio succinogenes), which grew on H 2 and fumarate producing succinate, keeping the H 2 concentration low (12). The interspecies cooperation allowed W. succinogenes to grow at the expense of H 2 produced by R. albus, but it also offered an energetic advantage to R. albus in the form of a higher ATP gain (4 mol of ATP instead of 3.3 mol of glucose fermented) and, consequently, a better growth yield (13). At low H 2 partial pressures, the free energy associated with glucose fermentation is more negative than that at high H 2 partial pressures, which is the thermodynamic basis for the different ATP gains (13). The fermentation of R. albus on glucose has been modeled (14). The literature on interspecies H 2 and formate transfer has been reviewed recently (15).Enzymatic analyses have revealed that R. albus strain 7 grown in batch culture on glucose contains an NAD-specific glyceraldehyde-3-phosphate dehydr...

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Section: Discussionmentioning

confidence: 99%

Hydrogen Formation and Its Regulation in Ruminococcus albus: Involvement of an Electron-Bifurcating [FeFe]-Hydrogenase, of a Non-Electron-Bifurcating [FeFe]-Hydrogenase, and of a Putative Hydrogen-Sensing [FeFe]-Hydrogenase

et al. 2014

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“…However, the identity of the redox acceptor for the R. capsulatus [NiFe] uptake hydrogenase remains unclear. One suggestion is that electrons can move directly from [NiFe] hydrogenases into the ubiquinone pool, where other unknown oxidoreductases can reduce soluble charge carriers to reduce nitrogenases ( 36 ).…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, Fds can have other roles in nitrogen fixation. Some Fds are involved in the maturation of nitrogenase cofactors, donating electrons to assembly proteins such as NifB ( 36 , 37 ).…”

Section: Introductionmentioning

confidence: 99%

Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase in Rhodobacter capsulatus

Addison,

Glatter,

K. A. Hochberg

et al. 2024

mBio

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Nitrogenases are the only enzymes able to fix gaseous nitrogen into bioavailable ammonia and hence are essential for sustaining life. Catalysis by nitrogenases requires both a large amount of ATP and electrons donated by strongly reducing ferredoxins or flavodoxins. Our knowledge about the mechanisms of electron transfer to nitrogenase enzymes is limited: The electron transport to the iron (Fe)-nitrogenase has hardly been investigated. Here, we characterized the electron transfer pathway to the Fe-nitrogenase in Rhodobacter capsulatus via proteome analyses, genetic deletions, complementation studies, and phylogenetics. Proteome analyses revealed an upregulation of four ferredoxins under nitrogen-fixing conditions reliant on the Fe-nitrogenase in a molybdenum nitrogenase knockout strain, compared to non-nitrogen-fixing conditions. Based on these findings, R. capsulatus strains with deletions of ferredoxin ( fdx ) and flavodoxin ( fld, nifF ) genes were constructed to investigate their roles in nitrogen fixation by the Fe-nitrogenase. R. capsulatus deletion strains were characterized by monitoring diazotrophic growth and Fe-nitrogenase activity in vivo . Only deletions of fdxC or fdxN resulted in slower growth and reduced Fe-nitrogenase activity, whereas the double deletion of both fdxC and fdxN abolished diazotrophic growth. Differences in the proteomes of ∆ fdxC and ∆ fdxN strains, in conjunction with differing plasmid complementation behaviors of fdxC and fdxN, indicate that the two Fds likely possess different roles and functions. These findings will guide future engineering of the electron transport systems to nitrogenase enzymes, with the aim of increased electron flux and product formation. IMPORTANCE Nitrogenases are essential for biological nitrogen fixation, converting atmospheric nitrogen gas to bioavailable ammonia. The production of ammonia by diazotrophic organisms, harboring nitrogenases, is essential for sustaining plant growth. Hence, there is a large scientific interest in understanding the cellular mechanisms for nitrogen fixation via nitrogenases. Nitrogenases rely on highly reduced electrons to power catalysis, although we lack knowledge as to which proteins shuttle the electrons to nitrogenases within cells. Here, we characterized the electron transport to the iron (Fe)-nitrogenase in the model diazotroph Rhodobacter capsulatus , showing that two distinct ferredoxins are very important for nitrogen fixation despite having different redox centers. In addition, our research expands upon the debate on whether ferredoxins have functional redundancy or perform distinct roles within cells. Here, we observe that both essential ferredoxins likely have distinct roles based on differential proteome shifts of deletion strains and different complementation behaviors.

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“…However, the identity of the redox acceptor for the R. capsulatus [NiFe] uptake hydrogenase remains unclear. One suggestion is that electrons can move directly from [NiFe] hydrogenase into the ubiquinone pool, where other unknown oxidoreductases can reduce soluble charge carriers to reduce nitrogenases [33] .…”

Section: Introductionmentioning

confidence: 99%

Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase inRhodobacter capsulatus

Addison,

Glatter,

Hochberg

et al. 2023

Preprint

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Nitrogenases are the only enzymes able to fix gaseous nitrogen into bioavailable ammonia and, hence, are essential for sustaining life. Catalysis by nitrogenases requires both a large amount of ATP and electrons donated by strongly reducing ferredoxins or flavodoxins. Our knowledge about the mechanisms of electron transfer to nitrogenase enzymes is limited: The electron transport to the iron (Fe)-nitrogenase has hardly been investigated. Here, we characterised the electron transfer pathway to the Fe-nitrogenase inRhodobacter capsulatusvia proteome analyses, genetic deletions, complementation studies and phylogenetics. Proteome analyses revealed an upregulation of four ferredoxins under nitrogen-fixing conditions reliant on the Fe-nitrogenase in a molybdenum nitrogenase knockout strain, compared to non-nitrogen-fixing conditions. Based on these findings,R. capsulatusstrains with deletions of ferredoxin (fdx) and flavodoxin (fld, nifF) genes were constructed to investigate their roles in nitrogen fixation by the Fe-nitrogenase.R. capsulatusdeletion strains were characterised by monitoring diazotrophic growth and Fe-nitrogenase activityin vivo. Only deletions offdxCorfdxNresulted in slower growth and reduced Fe-nitrogenase activity, whereas the double-deletion of bothfdxCandfdxNabolished diazotrophic growth. Differences in the proteomes of ΔfdxCand ΔfdxNstrains, in conjunction with differing plasmid complementation behaviours offdxCandfdxN, indicate that the two Fds likely possess different roles and functions. These findings will guide future engineering of the electron transport systems to nitrogenase enzymes, with the aim of increased electron flux and product formation.ImportanceNitrogenases are essential for biological nitrogen fixation, converting atmospheric nitrogen gas to bioavailable ammonia. Production of ammonia by diazotrophic organisms, harbouring nitrogenases, is essential for sustaining plant growth. Hence, there is a large scientific interest in understanding the cellular mechanisms for nitrogen fixation via nitrogenases. Nitrogenases rely on highly reduced electrons to power catalysis, though we lack knowledge as to which proteins shuttle the electrons to nitrogenases within cells. Here, we characterised the electron transport to the iron (Fe)-nitrogenase in the model diazotrophRhodobacter capsulatus, showing that two distinct ferredoxins are very important for nitrogen fixation despite having different redox centres. Additionally, our research expands upon the debate on whether ferredoxins have functional redundancy or perform distinct roles within cells. Here, we observe that both essential ferredoxins likely have distinct roles based on differential proteome shifts of deletion strains and different complementation behaviours.

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Regulation of Hydrogenase Gene Expression

Cited by 11 publications

References 88 publications

Hydrogen Formation and Its Regulation in Ruminococcus albus: Involvement of an Electron-Bifurcating [FeFe]-Hydrogenase, of a Non-Electron-Bifurcating [FeFe]-Hydrogenase, and of a Putative Hydrogen-Sensing [FeFe]-Hydrogenase

Hydrogen Formation and Its Regulation in Ruminococcus albus: Involvement of an Electron-Bifurcating [FeFe]-Hydrogenase, of a Non-Electron-Bifurcating [FeFe]-Hydrogenase, and of a Putative Hydrogen-Sensing [FeFe]-Hydrogenase

Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase in Rhodobacter capsulatus

Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase inRhodobacter capsulatus

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