A nitrite-oxidizing bacterium constitutively consumes atmospheric hydrogen

Chemolithoautotrophic nitrite-oxidizing bacteria (NOB) of the genus Nitrospira contribute to nitrification in diverse natural environments and engineered systems. Nitrospira are thought to be well-adapted to substrate limitation owing to their high affinity for nitrite and capacity to use alternative energy sources. Here, we demonstrate that the canonical nitrite oxidizer Nitrospira moscoviensis oxidizes hydrogen (H2) below atmospheric levels using a high-affinity group 2a nickel-iron hydrogenase [Km(app) = 32 nM]. Atmospheric H2 oxidation occurred under both nitrite-replete and nitrite-deplete conditions, suggesting low-potential electrons derived from H2 oxidation promote nitrite-dependent growth and enable survival during nitrite limitation. Proteomic analyses confirmed the hydrogenase was abundant under both conditions and indicated extensive metabolic changes occur to reduce energy expenditure and growth under nitrite-deplete conditions. Respirometry analysis indicates the hydrogenase and nitrite oxidoreductase are bona fide components of the aerobic respiratory chain of N. moscoviensis, though they transfer electrons to distinct electron carriers in accord with the contrasting redox potentials of their substrates. Collectively, this study suggests atmospheric H2 oxidation enhances the growth and survival of NOB in amid variability of nitrite supply. These findings also extend the phenomenon of atmospheric H2 oxidation to a seventh phylum (Nitrospirota) and reveal unexpected new links between the global hydrogen and nitrogen cycles.

Hydrogen evolution, electron-transfer, hydride-transfer reactions in a nickel-iron hydrogenase model complex: A theoretical study of the distinctive reactivities for the conformational isomers of nickel-iron hydride

Hydrogen fuel is a promising alternative to fossil fuel. Therefore, efficient hydrogen production is crucial to elucidate the distinctive reactivities of metal hydride species, the intermediates formed during hydrogen activation/evolution...

E. coli Nickel-Iron Hydrogenase 1 Catalyses Non-native Reduction of Flavins: Demonstration for Alkene Hydrogenation by Old Yellow Enzyme

<p>Robust [NiFe] hydrogenase 1 (Hyd1) from <i>Escherichia coli</i> is shown to have non-native, H₂-dependent activity for FMN and FAD reduction, and to function as a promising recycling system for FMNH₂ supply to flavoenzymes for chemical synthesis, giving a total turnover number over 10 thousand when coupled with an Old Yellow Enzyme ene reductase. </p>

E. coli Nickel-Iron Hydrogenase 1 Catalyses Non-native Reduction of Flavins: Demonstration for Alkene Hydrogenation by Old Yellow Enzyme

<p>Robust [NiFe] hydrogenase 1 (Hyd1) from <i>Escherichia coli</i> is shown to have non-native, H₂-dependent activity for FMN and FAD reduction, and to function as a promising recycling system for FMNH₂ supply to flavoenzymes for chemical synthesis, giving a total turnover number over 10 thousand when coupled with an Old Yellow Enzyme ene reductase. </p>

E. coli Nickel-Iron Hydrogenase 1 Catalyses Non-native Reduction of Flavins: Demonstration for Alkene Hydrogenation by Old Yellow Enzyme

<p>Robust [NiFe] hydrogenase 1 (Hyd1) from <i>Escherichia coli</i> is shown to have non-native, H₂-dependent activity for FMN and FAD reduction, and to function as a promising recycling system for FMNH₂ supply to flavoenzymes for chemical synthesis, giving a total turnover number over 10 million when coupled with an Old Yellow Enzyme ene reductase. </p>

Synthetic Models for Nickel–Iron Hydrogenase Featuring Redox-Active Ligands

The nickel–iron hydrogenase enzymes efficiently and reversibly interconvert protons, electrons, and dihydrogen. These redox proteins feature iron–sulfur clusters that relay electrons to and from their active sites. Reported here are synthetic models for nickel–iron hydrogenase featuring redox-active auxiliaries that mimic the iron–sulfur cofactors. The complexes prepared are NiII(μ-H)FeIIFeII species of formula [(diphosphine)Ni(dithiolate)(μ-H)Fe(CO)2(ferrocenylphosphine)]+ or NiIIFeIFeII complexes [(diphosphine)Ni(dithiolate)Fe(CO)2(ferrocenylphosphine)]+ (diphosphine = Ph2P(CH2)2PPh2 or Cy2P(CH2)2PCy2; dithiolate = –S(CH2)3S–; ferrocenylphosphine = diphenylphosphinoferrocene, diphenylphosphinomethyl(nonamethylferrocene) or 1,1′-bis(diphenylphosphino)ferrocene). The hydride species is a catalyst for hydrogen evolution, while the latter hydride-free complexes can exist in four redox states – a feature made possible by the incorporation of the ferrocenyl groups. Mixed-valent complexes of 1,1′-bis(diphenylphosphino)ferrocene have one of the phosphine groups unbound, with these species representing advanced structural models with both a redox-active moiety (the ferrocene group) and a potential proton relay (the free phosphine) proximal to a nickel–iron dithiolate.