Bacterial hydrogenases for biohydrogen technology

Hydrogen gas is among a 'basket of solutions' for future energy needs. At present 99% of hydrogen is produced by reforming fossil fuels and 1% comes from electrolysis. Most is used directly by industry, but increasingly it is being used as a fuel. Hydrogen has the highest energy per weight of any fuel, and its use (particularly in a fuel cell) is clean and efficient. As the immediate product of energizing water by photolysis (sunlight) or renewable-powered electrolysis, hydrogen is the 'greenest' and most renewable of fuels. This fact is attracting major research funding in advanced countries, particularly USA, Australia, Germany and Sweden. The drawbacks of hydrogen are frequently voiced - low energy density, difficulty in storage (a disadvantage for small vehicles), primitive supply and distribution infrastructure - but these issues cannot hold back its development, and H2 will eventually be an important and even dominant part of human lives and economies. Biohydrogen is the production or oxidation of hydrogen by organisms. The scope for tapping into this resource constructively is enormous; yet hydrogen is also a nutrient for pathogens. Hydrogen is a byproduct of ammonia synthesis by microorganisms contained in plant root nodules, using an enzyme (catalyst) known as nitrogenase. Hydrogen is also produced and used as a fuel by a vast range of microorganisms. The chemistry depends upon oxygen-sensitive enzymes known as hydrogenases, which are essential to much of the microbial world, including strict soil aerobes, green algae that can be adapted to produce hydrogen, methane-producers, and some notorious human pathogens such as Helicobacter and Salmonella. Indeed, the efficiency of hydrogenases is crucial to bacterial virulence. We and others have proposed that the active sites of hydrogenases are as active as platinum - an expensive and limited resource. This has raised interest in their exploitation as actual or inspirational catalysts in electronic/fuel cell/sensor devices. Understanding and consequently being able to control the activity and oxygen-tolerance of hydrogenases within the cell are therefore among the most important factors in bringing about a future, fully renewable, and healthy H2 energy technology. The Oxford and Dundee laboratories are superbly complementary. The Dundee group has internationally-recognised expertise in studying the cell biology of hydrogenases in the common gut bacterium E. coli and the notorious pathogen, Salmonella. The Oxford group have pioneered a physical method for studying hydrogenases, which reveals, rapidly and accurately, all of their important catalytic properties. The method is an electrochemical technique known as protein film electrochemistry, and it involves the enzyme being attached to an electrode surface. The precise data that are obtained help guide further investigations, saving large amounts of research time and money that is spent worldwide on developing biohydrogen. The attachment of the enzyme molecule to an electrode is analogous to 'wiring' it to an electrical circuit, and in the process the enzyme is able to function as a practical electrocatalyst, able to produce electricity from hydrogen or hydrogen from electricity or light (if the enzyme is attached to light-sensitive particles).

Biohydrogen is the production or oxidation of H2 by organisms. The scope for tapping into this resource for future energy is enormous; yet H2 is also a nutrient for pathogens. Hydrogen is produced and oxidised by a vast range of microorganisms, mainly using oxygen-sensitive enzymes known as hydrogenases. Hydrogen-based metabolism is essential for strict soil aerobes, methane-producers, notorious human pathogens such as Helicobacter and Salmonella, and even green algae that produce H2. The active sites contain Fe or Fe and Ni, coordinated by the unusual ligands CO and CN?, and we and others have proposed that the active sites of hydrogenases are as active as platinum - an expensive and limited resource. This has raised interest in their exploitation as actual or inspirational catalysts in electronic/fuel cell/sensor devices. Understanding the activity and O2-sensitivity of hydrogenases in organisms is one of the most important factors in bringing about a future, fully renewable, and healthy H2 energy technology. The Oxford and Dundee laboratories are superbly complementary. The Dundee group has internationally-recognised expertise in cell and molecular biology of hydrogenases, particularly E. coli and Salmonella. The Oxford group have pioneered a physical method- protein film electrochemistry- for studying hydrogenases; this reveals, rapidly and accurately, all important catalytic properties, with the enzyme attached to an electrode surface. The catalytic activity is recorded as electrical current and enzyme reactions are controlled through the electrode potential. The precise data that are obtained guide further investigations, saving large amounts of research time and money. Attaching an enzyme molecule to an electrode is analogous to 'wiring' it to an electrical circuit: the enzyme becomes a practical electrocatalyst, able to produce electricity from H2,, or H2 from electricity (or light, if attached to a photosensitive particle).