Bio-Hydrogen

Hydrogenases, enzymes involved in the microbial production and consumption of hydrogen gas, were first described in a series of classic papers in the Biochemical Journal by Stephenson and Stickland in the 1930s. The enzymes came to prominence during the fuel crisis of the 1970s, when it became apparent that reserves of fossil fuels were finite and biological hydrogen production offered a sustainable alternative. Since then, the prospect of climate change has spurred the search for sources of hydrogen that do not involve net production of CO2. There has been steady progress in our understanding of hydrogen in the biosphere. Hydrogen is produced by photosynthetic cleavage of water, by fermentation of waste materials, and as a by-product of nitrogen fixation. How we could make this bio-hydrogen into a viable fuel source is certainly a challenge for the future. It will not be possible until we understand, in much more detail, how and why organisms produce hydrogen.
It became obvious early on that economic hydrogen production it is not just a matter of extracting enzymes or growing monocultures of hydrogen-producing organisms and using them like chemical catalysts. Microbes have their own agenda. Hydrogenases are complex enzymes; their synthesis depends on complex multi-step assembly processes, which are now being elucidated. They use complex machinery to transport the hydrogenases, complete with their elaborate nickel- and iron-containing centres, specifically through cell membranes. Moreover organisms in the environment are accustomed to exchanging metabolites, including hydrogen, to optimize their use of energy sources; production of hydrogen and hydrogenases is tightly regulated. Details are emerging of their mechanisms of control of biosynthesis and environmental hydrogen sensing, by regulatory proteins very similar to hydrogenases.