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Hydrogen Production From Blue Green Algae: Solar Fuels

Jon Van Wagenen

Fossil energy is a limited resource, and the production of carbon dioxide is leading to global warming. Meanwhile, the population of the world continues to increase, as does the amount of energy that each person uses. The world is in need of new, clean and renewable energy sources.

Fortunately, enough energy strikes the surface of the earth in an hour to provide all the energy used in a year. By finding ways to capture some of this energy, future energy needs may be met. The world’s infrastructure relies on having fuels, so electricity alone cannot solve the problem. Photovoltaic solar cells convert sunlight into electricity, which must be fed into the grid, or stored in a battery. Solar concentrators use mirrors to concentrate solar radiation to a small area to create heat energy, which is used to heat water or create electricity. Corn, soy and other plants can be processed into fuels, but they compete with agricultural land and drive up the price of food. Photosynthetic microbes, like algae or cyanobacteria (blue-green algae) could be a solution that creates fuel directly from sunlight without competing with agriculture. All microbes are partially composed of oils, which can be extracted from them. However, why burn oil when you can produce clean hydrogen?

Some strains of cyanobacteria produce hydrogen. One of these is Nostoc punctiforme, which fixes nitrogen from the air when it grows and makes hydrogen as a byproduct. However it has a protein to reuse this hydrogen. When this protein is eliminated by genetic mutation, the cells give away hydrogen as they grow. However, getting these mutants to grow at a larger scale has been a problem. For some reason the cells stick to each other and the surfaces they came in contact with.

In this work, a new system was developed to culture the cells by providing extra nitrogen at the beginning of the growth. This allowed the first large-scale culture of the cells to be achieved. However, even in this system, the cells had a tendency to clump when the nitrogen ran out. It was hypothesized that the cells may have differentiated into a special state, called hormogonia, that they form in nature to move when they face stressful

conditions. Therefore, a technique known as qPCR was employed to study whether mutant cells had increased expression of genes that are known to be related to the hormogonium state. It was found that at least one gene, named pilQ, was regulated differently in the mutants than the wild type.

The implications of this finding are that a strategy for dealing with hormogonia should be incorporated into plans for growing the mutant in larger scales. One strategy is to reduce the amount of stress the cells feel by giving them extra nutrients or scaling back the amount of light or mixing. Another strategy is to immobilize the cells. This means growing them on a three-dimensional support, for example the kind of foam that makes car seats soft.

When cells are immobilized, they may be easier to handle and produce hydrogen more efficiently. The hormogonium phase could even be useful to immobilization. As the

understanding of the cellular processes of cyanobacteria increases, the field becomes closer to being able to use them as a fuel source for the future.

Degree project in biology, Master of science (2 years), 2010 Examensarbete i biologi 45 hp till masterexamen, 2010

Biology Education Centre and Department of Photochemistry and Molecular Science, Uppsala University Supervisors: Peter Lindblad and Thorsten Heidorn

References

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