Storage of solar energy as hydrogen provides a platform towards decarbonizing our economy. One emerging strategy for the production of solar fuels is to use photocatalytic biohybrid systems that ...combine the high catalytic activity of non‐photosynthetic microorganisms with the high light‐harvesting efficiency of metal semiconductor nanoparticles. However, few such systems have been tested for H2 production. We investigated light‐driven H2 production by three novel organisms, Desulfovibrio desulfuricans, Citrobacter freundii, and Shewanella oneidensis, self‐photosensitized with cadmium sulfide nanoparticles, and compared their performance to Escherichia coli. All biohybrid systems produced H2 from light, with D. desulfuricans‐CdS demonstrating the best activity overall and outperforming the other microbial systems even in the absence of a mediator. With this system, H2 was continuously produced for more than 10 days with a specific rate of 36 μmol gdcw−1 h−1. High apparent quantum yields of 23 % and 4 % were obtained, with and without methyl viologen, respectively, exceeding values previously reported.
Novel biohybrid systems are created for light‐driven H2 production by using non‐photosynthetic microorganisms self‐photosensitized with CdS nanoparticles. An outstanding biohybrid system using D. desulfuricans displays high H2 production activity, high stability and a remarkable solar efficiency.
Microbial sulfate reduction has governed Earth's biogeochemical sulfur cycle for at least 2.5 billion years. However, the enzymatic mechanisms behind this pathway are incompletely understood, ...particulary for the reduction of sulfite—a key intermediate in the pathway. This critical reaction is performed by DsrAB, a widespread enzyme also involved in other dissimilatory sulfur metabolisms. Using in vitro assays with an archaeal DsrAB, supported with genetic experiments in a bacterial system, we show that the product of sulfite reduction by DsrAB is a protein-based trisulfide, in which a sulfite-derived sulfur is bridging two conserved cysteines of DsrC. Physiological studies also reveal that sulfate reduction rates are determined by cellular levels of DsrC. Dissimilatory sulfate reduction couples the four-electron reduction of the DsrC trisulfide to energy conservation.
The performance of heterogeneous catalysts for electrocatalytic CO2 reduction suffers from unwanted side reactions and kinetic inefficiencies at the required large overpotential. However, immobilized ...CO2 reduction enzymes—such as formate dehydrogenase—can operate with high turnover and selectivity at a minimal overpotential and are therefore ‘ideal’ model catalysts. Here, through the co-immobilization of carbonic anhydrase, we study the effect of CO2 hydration on the local environment and performance of a range of disparate CO2 reduction systems from enzymatic (formate dehydrogenase) to heterogeneous systems. We show that the co-immobilization of carbonic anhydrase increases the kinetics of CO2 hydration at the electrode. This benefits enzymatic CO2 reduction—despite the decrease in CO2 concentration—due to a reduction in local pH change, whereas it is detrimental to heterogeneous catalysis (on Au) because the system is unable to suppress the H2 evolution side reaction. Understanding the role of CO2 hydration kinetics within the local environment on the performance of electrocatalyst systems provides important insights for the development of next-generation synthetic CO2 reduction catalysts.Carbonic anhydrase enzymatically catalyses CO2 hydration, and its effect on enzymatic and heterogeneous CO2 reduction has now been studied. Through the co-immobilization of carbonic anhydrase, it has been shown that faster CO2 hydration kinetics are beneficial for enzymatic catalysis (using formate dehydrogenase) but detrimental for heterogeneous catalysts, such as gold.
The integration of enzymes with synthetic materials allows efficient electrocatalysis and production of solar fuels. Here, we couple formate dehydrogenase (FDH) from Desulfovibrio vulgaris ...Hildenborough (DvH) to metal oxides for catalytic CO2 reduction and report an in‐depth study of the resulting enzyme–material interface. Protein film voltammetry (PFV) demonstrates the stable binding of FDH on metal‐oxide electrodes and reveals the reversible and selective reduction of CO2 to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR‐IR) spectroscopy confirm a high binding affinity for FDH to the TiO2 surface. Adsorption of FDH on dye‐sensitized TiO2 allows for visible‐light‐driven CO2 reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11±1 s−1. The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in the selective photoreduction of aqueous CO2 to formate.
Electro‐ and solar‐driven CO2 utilization: Reversible electrocatalysis with formate dehydrogenase on porous metal oxides is established. A self‐assembled colloidal system containing formate dehydrogenase immobilized on dye‐sensitized TiO2 provides a benchmark for the selective reduction of CO2 to formate in aqueous solution.
Solar-driven coupling of water oxidation with CO2 reduction sustains life on our planet and is of high priority in contemporary energy research. Here, we report a photoelectrochemical tandem device ...that performs photocatalytic reduction of CO2 to formate. We employ a semi-artificial design, which wires a W-dependent formate dehydrogenase (FDH) cathode to a photoanode containing the photosynthetic water oxidation enzyme, Photosystem II, via a synthetic dye with complementary light absorption. From a biological perspective, the system achieves a metabolically inaccessible pathway of light-driven CO2 fixation to formate. From a synthetic point of view, it represents a proof-of-principle system utilizing precious-metal-free catalysts for selective CO2-to-formate conversion using water as an electron donor. This hybrid platform demonstrates the translatability and versatility of coupling abiotic and biotic components to create challenging models for solar fuel and chemical synthesis.
Microbial dissimilatory sulfur metabolism utilizing dissimilatory sulfite reductases (Dsr) influenced the biochemical sulfur cycle during Earth's history and the Dsr pathway is thought to be an ...ancient metabolic process. Here we performed comparative genomics, phylogenetic, and synteny analyses of several Dsr proteins involved in or associated with the Dsr pathway across over 195,000 prokaryotic metagenomes. The results point to an archaeal origin of the minimal DsrABCMK(N) protein set, having as primordial function sulfite reduction. The acquisition of additional Dsr proteins (DsrJOPT) increased the Dsr pathway complexity. Archaeoglobus would originally possess the archaeal-type Dsr pathway and the archaeal DsrAB proteins were replaced with the bacterial reductive-type version, possibly at the same time as the acquisition of the QmoABC and DsrD proteins. Further inventions of two Qmo complex types, which are more spread than previously thought, allowed microorganisms to use sulfate as electron acceptor. The ability to use the Dsr pathway for sulfur oxidation evolved at least twice, with Chlorobi and Proteobacteria being extant descendants of these two independent adaptations.
Mo/W formate dehydrogenases catalyze the reversible reduction of CO2 species to formate. It is thought that the substrate is CO2 and not a hydrated species like HCO3−, but there is still no ...indisputable evidence for this, in spite of the extreme importance of the nature of the substrate for mechanistic studies. We devised a simple electrochemical method to definitively demonstrate that the substrate of formate dehydrogenases is indeed CO2.
A simple, inexpensive and fast method based on protein film electrochemistry is proposed to discriminate whether CO2 or HCO3− is the substrate of any catalyst interacting with an electrode. In this study, CO2 rather than HCO3− is found to be the substrate of both formate dehydrogenase and CO dehydrogenase.
Early bioenergetic evolution Sousa, Filipa L.; Thiergart, Thorsten; Landan, Giddy ...
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
07/2013, Letnik:
368, Številka:
1622
Journal Article
Recenzirano
Odprti dostop
Life is the harnessing of chemical energy in such a way that the energy-harnessing device makes a copy of itself. This paper outlines an energetically feasible path from a particular inorganic ...setting for the origin of life to the first free-living cells. The sources of energy available to early organic synthesis, early evolving systems and early cells stand in the foreground, as do the possible mechanisms of their conversion into harnessable chemical energy for synthetic reactions. With regard to the possible temporal sequence of events, we focus on: (i) alkaline hydrothermal vents as the far-from-equilibrium setting, (ii) the Wood–Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes, (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria, respectively. In terms of the main evolutionary transitions in early bioenergetic evolution, we focus on: (i) thioester-dependent substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent–ocean interface via the ATP synthase, (iii) harnessing of Na+ gradients generated by H+/Na+ antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent) proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately, all of these bioenergetic processes depend, even today, upon CO2 reduction with low-potential ferredoxin (Fd), generated either chemosynthetically or photosynthetically, suggesting a reaction of the type ‘reduced iron → reduced carbon’ at the beginning of bioenergetic evolution.
Abstract
Organohalide-respiring bacteria are key organisms for the bioremediation of soils and aquifers contaminated with halogenated organic compounds. The major players in this process are ...respiratory reductive dehalogenases, corrinoid enzymes that use organohalides as substrates and contribute to energy conservation. Here, we present the structure of a menaquinol:organohalide oxidoreductase obtained by cryo-EM. The membrane-bound protein was isolated from
Desulfitobacterium hafniense
strain TCE1 as a PceA
2
B
2
complex catalysing the dechlorination of tetrachloroethene. Two catalytic PceA subunits are anchored to the membrane by two small integral membrane PceB subunits. The structure reveals two menaquinone molecules bound at the interface of the two different subunits, which are the starting point of a chain of redox cofactors for electron transfer to the active site. In this work, the structure elucidates how energy is conserved during organohalide respiration in menaquinone-dependent organohalide-respiring bacteria.
While the importance of sulfur transfer reactions is well established for a number of biosynthetic pathways, evidence has only started to emerge that sulfurtransferases may also be major players in ...sulfur-based microbial energy metabolism. Among the first organisms studied in this regard is the phototrophic purple sulfur bacterium Allochromatium vinosum. During the oxidation of reduced sulfur species to sulfate this Gammaproteobacterium accumulates sulfur globules. Low molecular weight organic persulfides have been proposed as carrier molecules transferring sulfur from the periplasmic sulfur globules into the cytoplasm where it is further oxidized via the "Dsr" (dissimilatory sulfite reductase) proteins. We have suggested earlier that the heterohexameric protein DsrEFH is the direct or indirect acceptor for persulfidic sulfur imported into the cytoplasm. This proposal originated from the structural similarity of DsrEFH with the established sulfurtransferase TusBCD from E. coli. As part of a system for tRNA modification TusBCD transfers sulfur to TusE, a homolog of another crucial component of the A. vinosum Dsr system, namely DsrC. Here we show that neither DsrEFH nor DsrC have the ability to mobilize sulfane sulfur directly from low molecular weight thiols like thiosulfate or glutathione persulfide. However, we demonstrate that DsrEFH binds sulfur specifically to the conserved cysteine residue DsrE-Cys78 in vitro. Sulfur atoms bound to cysteines in DsrH and DsrF were not detected. DsrC was exclusively persulfurated at DsrC-Cys111 in the penultimate position of the protein. Most importantly, we show that persulfurated DsrEFH indeed serves as an effective sulfur donor for DsrC in vitro. The active site cysteines Cys78 of DsrE and Cys20 of DsrH furthermore proved to be essential for sulfur oxidation in vivo supporting the notion that DsrEFH and DsrC are part of a sulfur relay system that transfers sulfur from a persulfurated carrier molecule to the dissimilatory sulfite reductase DsrAB.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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