Advancing Biotechnologies for Fuel Generation: Exploiting Transmembrane Cytochromes for Solar Energy Conversion

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Reports concerning dwindling reserves of fossil fuels and concerns over fuel security are frequent news headlines. The rising costs of fuel are a daily reminder of the challenges faced by a global society with ever increasing energy demands. In this context it is perhaps surprising that so many of the renewable energy supplies available to us, namely, sunlight, winds and waves, remain largely untapped resources. This is mainly due to the challenges that exist in converting these energy forms into fuels from which energy can be released 'on demand' when we wish to play computer games, drive a car and so on. However, during plant photosynthesis fuels are made naturally from the energy in sunlight. Light absorption by the green chlorophyll pigments generates an energised electron that is directed, along chains of metal centres, to catalysts that make sugars. These sugars fuel us, and all animals, when their energy is released following digestion of a meal. However, using farmed plants to produce biofuels is controversial as agriculture is also required to feed the world. As a consequence, and inspired by natural processes, we propose to build a system for artificial photosynthesis. In essence, we wish to place tiny solar-panels on microbes in order to harness sunlight to drive the production of hydrogen - a fuel from which the technologies to release energy on demand are well-advanced. We will use dyes and semi-conductor particles as mechanically and chemically robust materials to capture the energy in sunlight and generate energised electrons. We will couple these particles to biology's version of conducting wires. These wires are made from heme proteins that span membranes that provide Nature's solution to compartmentalising water-filled chambers (i.e., the inside of the bacterium). The heme-wires are produced naturally by 'rock-breathing' microorganisms and after these wires have transferred the energised electrons across the membrane they will drive enzyme catalysis to produce hydrogen Our novel bio-mimetic photocatalysts will establish new principles for the design of homogeneous photocatalysts with spatially segregated sites for fuel-evolution and the supply of electrons that is needed to sustain this process. We imagine that our photocatalysts will proove versatile and that with slight modification they will be able to harness solar energy for the manufacture of drugs and fine chemicals.