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Green Algae Step on the Gas

December 13, 2001

Whether it is in the shape of bread rolls, crunchy flakes or 'spaghetti al pesto di mare', the food industry is on an 'algae trip', selling these marine flora to health-conscious consumers as delicious energy-rich additions to their products. Yet there is another way that algae can help us to solve our energy problems: some of them can produce hydrogen which will, in the future, make it possible to run cars or supply laptops with electricity. Researchers from the University of Bonn have now isolated the gene responsible for producing hydrogen in green algae, and have genetically modified a strain of algae so that it can produce more than twice as much hydrogen than before.

'Hydrogen is a good store of energy,' Dr. Thomas Happe from the University of Bonn's Botanical Institute explains. 'The algae are therefore losing energy when they emit hydrogen to their environment.' In fact, some types of green algae will only do that if forced: for this purpose the Californian firm Melis Energy, with which the Bonn researchers are co-operating, has put them on a sulphur diet - sulphur is a component of many vital cell proteins. The algae then switch their metabolism to energy-saving mode, while part of their photosynthesis continues to run at maximum capacity, producing large amounts of energy-rich compounds which the cells can no longer utilise. As a result, they eventually 'dispose of' the excess energy in the form of hydrogen.

The colourless, non-toxic gas could soon come out in a big way: experts see it as the energy source of the future, capable of fuelling cars and buses and able to provide digital cameras, mobile phones and laptops with power for hours on end. This revolution is made possible by further developments in the fuel cell. In it, hydrogen reacts with the oxygen in the air to form water, producing electricity at the same time - for example, to power electric motors. The advantage is that water can then be split into oxygen and hydrogen by using energy. If solar power is used to maintain this cycle, in theory at least no pollutant substances will be involved. And in contrast to the electrical energy produced by solar cells, there are no major problems with storing hydrogen - only in this way can we guarantee that the appropriate appliances will work when the sun is not shining.

For sixty years it has been known in principle that green algae can produce oxygen and hydrogen from water. In this process they are assisted by a cellular protein, the enzyme hydrogenase; the energy required is provided by photosynthesis. Dr. Happe and his team have succeeded in isolating the gene with the structural plan of the hydrogenase from various kinds of green algae.

The researchers are now attempting to decipher the spatial structure of the enzyme. In this way they hope to discover how the partners in the reaction are adsorbed by the protein and how it catalyses the formation of hydrogen. The experiments involved are complex - to date the Bonn team has therefore been using computer images, which come pretty close to reality.

'Our hydrogenase has a very simple structure,' Dr. Happe explains, 'and this of course makes it easier to understand how it functions.' This is why their findings have attracted great interest worldwide - particularly since the enzyme produces large amounts of hydrogen. In an international project, which is funded by the Japanese energy ministry, the research team is now trying not only to isolate the photosynthesis systems but also the hydrogenase from blue and green algae and to fix them to artificial membranes. Their calculation is that this type of 'biochemical battery', which requires relatively little maintenance, could produce hydrogen when exposed to sunlight.

It is simpler, however, to set the green algae to work directly in energy production - as one-celled 'galley slaves', as it were. Yet the synthesis of hydrogen is a defence mechanism for green algae, which is only activated when food is scarce. Normally, the hydrogenase concentration in the algae cells is correspondingly low - and the less hydrogenase is present, the less hydrogen is emitted. For this reason the Bonn research team has added a turbocharger to the hydrogenase gene which ensures that the genetic information is accessed more frequently, with the result that the alga produces more enzyme. The result is a success: the alga with the turbocharger produces twice to three times as much hydrogen as its cousins out in the wild. 'We now need to subject this mutation to more precise genetic scrutiny,' Dr. Happe explains. 'However, we regard this success as the first step towards the large-scale production of hydrogen.'

Bonn, Universitaet