Capture of carbon dioxide and hydrogen by engineered Escherichia coli: hydrogen-dependent CO reduction to formate.

In times of global climate change and the fear of dwindling resources, we are facing different considerable challenges such as the replacement of fossil fuel-based energy carriers with the coincident maintenance of the increasing energy supply of our growing world population. Therefore, CO capturing and H storing solutions are urgently needed. In this study, we demonstrate the production of a functional and biotechnological interesting enzyme complex from acetogenic bacteria, the hydrogen-dependent CO reductase (HDCR), in the well-known model organism Escherichia coli.

Complex Multimeric [FeFe] Hydrogenases: Biochemistry, Physiology and New Opportunities for the Hydrogen Economy.

Hydrogenases are key enzymes of the energy metabolism of many microorganisms. Especially in anoxic habitats where molecular hydrogen (H) is an important intermediate, these enzymes are used to expel excess reducing power by reducing protons or they are used for the oxidation of H as energy and electron source. Despite the fact that hydrogenases catalyze the simplest chemical reaction of reducing two protons with two electrons it turned out that they are often parts of multimeric enzyme complexes catalyzing complex chemical reactions with a multitude of functions in the metabolism.

Hydrogenation of CO at ambient pressure catalyzed by a highly active thermostable biocatalyst.

Background: Replacing fossil fuels as energy carrier requires alternatives that combine sustainable production, high volumetric energy density, easy and fast refueling for mobile applications, and preferably low risk of hazard. Molecular hydrogen (H) has been considered as promising alternative; however, practical application is struggling because of the low volumetric energy density and the explosion hazard when stored in large amounts. One way to overcome these limitations is the transient conversion of H into other chemicals with increased volumetric energy density and lower risk hazard, for example so-called liquid organic hydrogen carriers such as formic acid/formate that is obtained by hydrogenation of CO.

Efficient whole cell biocatalyst for formate-based hydrogen production.

Background: Molecular hydrogen (H) is an attractive future energy carrier to replace fossil fuels. Biologically and sustainably produced H could contribute significantly to the future energy mix. However, biological H production methods are faced with multiple barriers including substrate cost, low production rates, and low yields.

Energetics and Application of Heterotrophy in Acetogenic Bacteria.

Acetogenic bacteria are a diverse group of strictly anaerobic bacteria that utilize the Wood-Ljungdahl pathway for CO2 fixation and energy conservation. These microorganisms play an important part in the global carbon cycle and are a key component of the anaerobic food web. Their most prominent metabolic feature is autotrophic growth with molecular hydrogen and carbon dioxide as the substrates.

A bacterial hydrogen-dependent CO2 reductase forms filamentous structures.

Interconversion of CO2 and formic acid is an important reaction in bacteria. A novel enzyme complex that directly utilizes molecular hydrogen as electron donor for the reversible reduction of CO2 has recently been identified in the Wood-Ljungdahl pathway of an acetogenic bacterium. This pathway is utilized for carbon fixation as well as energy conservation.

Ethylene Glycol Metabolism in the Acetogen Acetobacterium woodii.

Unlabelled: The acetogenic bacterium Acetobacterium woodii is able to grow by the oxidation of diols, such as 1,2-propanediol, 2,3-butanediol, or ethylene glycol. Recent analyses demonstrated fundamentally different ways for oxidation of 1,2-propanediol and 2,3-butanediol. Here, we analyzed the metabolism of ethylene glycol.

Nonacetogenic growth of the acetogen Acetobacterium woodii on 1,2-propanediol.

Acetogenic bacteria can grow by the oxidation of various substrates coupled to the reduction of CO2 in the Wood-Ljungdahl pathway. Here, we show that growth of the acetogen Acetobacterium woodii on 1,2-propanediol (1,2-PD) as the sole carbon and energy source is independent of acetogenesis. Enzymatic measurements and metabolite analysis revealed that 1,2-PD is dehydrated to propionaldehyde, which is further oxidized to propionyl coenzyme A (propionyl-CoA) with concomitant reduction of NAD.

Autotrophy at the thermodynamic limit of life: a model for energy conservation in acetogenic bacteria.

Life on earth evolved in the absence of oxygen with inorganic gases as potential sources of carbon and energy. Among the alternative mechanisms for carbon dioxide (CO₂) fixation in the living world, only the reduction of CO₂ by the Wood-Ljungdahl pathway, which is used by acetogenic bacteria, complies with the two requirements to sustain life: conservation of energy and production of biomass. However, how energy is conserved in acetogenic bacteria has been an enigma since their discovery.

The ferredoxin:NAD+ oxidoreductase (Rnf) from the acetogen Acetobacterium woodii requires Na+ and is reversibly coupled to the membrane potential.

The anaerobic acetogenic bacterium Acetobacterium woodii has a novel Na(+)-translocating electron transport chain that couples electron transfer from reduced ferredoxin to NAD(+) with the generation of a primary electrochemical Na(+) potential across its cytoplasmic membrane. In previous assays in which Ti(3+) was used to reduce ferredoxin, Na(+) transport was observed, but not a Na(+) dependence of the electron transfer reaction. Here, we describe a new biological reduction system for ferredoxin in which ferredoxin is reduced with CO, catalyzed by the purified acetyl-CoA synthase/CO dehydrogenase from A.

A bacterial electron-bifurcating hydrogenase.

The Wood-Ljungdahl pathway of anaerobic CO(2) fixation with hydrogen as reductant is considered a candidate for the first life-sustaining pathway on earth because it combines carbon dioxide fixation with the synthesis of ATP via a chemiosmotic mechanism. The acetogenic bacterium Acetobacterium woodii uses an ancient version of the pathway that has only one site to generate the electrochemical ion potential used to drive ATP synthesis, the ferredoxin-fueled, sodium-motive Rnf complex. However, hydrogen-based ferredoxin reduction is endergonic, and how the steep energy barrier is overcome has been an enigma for a long time.

An ancient pathway combining carbon dioxide fixation with the generation and utilization of a sodium ion gradient for ATP synthesis.

Synthesis of acetate from carbon dioxide and molecular hydrogen is considered to be the first carbon assimilation pathway on earth. It combines carbon dioxide fixation into acetyl-CoA with the production of ATP via an energized cell membrane. How the pathway is coupled with the net synthesis of ATP has been an enigma.