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Algae are a promising source of biofuels: besides being easy to grow and handle, some varieties are rich in oil similar to that produced by soybeans. Algae also produce another fuel: hydrogen. They make a small amount of hydrogen naturally during photosynthesis, but Anastasios Melis, a plant- and microbial-biology professor at the University of California, Berkeley, believes that genetically engineered versions of the tiny green organisms have a good shot at being a viable source for hydrogen.

Melis has created mutant algae that make better use of sunlight than their natural cousins do. This could increase the hydrogen that the algae produce by a factor of three. It would also boost the algae’s production of oil for biofuels.

The new finding will be important in maximizing the production of hydrogen in large-scale, commercial bioreactors. In a laboratory, Melis says, “[we make] low-density cultures and have thin bottles so that light penetrates from all sides.” Because of this, the cells use all the light falling on them. But in a commercial bioreactor, where dense algae cultures would be spread out in open ponds under the sun, the top layers of algae absorb all the sunlight but can only use a fraction of it.

Melis and his colleagues are designing algae that have less chlorophyll so that they absorb less sunlight. That means more light penetrates into the deeper algae layers, and eventually, more cells use the sunlight to make hydrogen.

The researchers manipulate the genes that control the amount of chlorophyll in the algae’s chloroplasts, the cellular organs that are the centers for photosynthesis. Each chloroplast naturally has 600 chlorophyll molecules. So far, the researchers have reduced this number by half. They plan to reduce the size further, to 130 chlorophyll molecules. At that point, dense cultures of algae in big bioreactors would make three times as much hydrogen as they make now, Melis says.

“If you can increase the productivity by means of thinning out the [chlorophyll], it’s going to affect any product that you make,” says Rolf Mehlhorn, an energy technologist at the Lawrence Berkeley National Laboratory. Algae that use sunlight more effectively would produce more oil, he says. Startups such as Solix Biofuels, based in Fort Collins, CO, and LiveFuels, based in Menlo Park, CA, are trying to extract oil from algae; the oil can be refined to make diesel and jet fuel.

The process is still at least five years from being used for hydrogen generation. Researchers will first have to increase the algae’s capacity to produce hydrogen. During normal photosynthesis, algae focus on using the sun’s energy to convert carbon dioxide and water into glucose, releasing oxygen in the process. Only about 3 to 5 percent of photosynthesis leads to hydrogen. Melis estimates that, if the entire capacity of the photosynthesis of the algae could be directed toward hydrogen production, 80 kilograms of hydrogen could be produced commercially per acre per day.

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Credit: Anastasios Melis, University of California, Berkeley

Tagged: Energy

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