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Algae-in-a-vat may power the future

green algae

Green algae like this could one day help drive a hydrogen economy (Image: Solar Bio-fuels Consortium)

Genetically modified green algae could one day produce stored energy in the form of hydrogen gas, say Australian researchers, fuelling a hydrogen economy. Associate Professor Ben Hankamer of the University of Queensland and colleagues report they have increased the sunlight-capturing efficiency of algae that can pump out hydrogen. If successfully scaled up, the researchers say this could complement or be an alternative to our present carbon-based economy. "We urgently need to develop and install new CO2-free energy production systems. Our systems offer one solution for this," the researchers say. They report their findings in the latest issue of the Plant Biotechnology Journal. The researchers have been studying single-celled photosynthetic algae (Chlamydomonas reinhardtii). The algae have evolved two kinds of photosynthesis, one of which produces hydrogen gas under low-sulfur conditions. It's this hydrogen gas that the team hopes to harvest from a bioreactor, a concentrated mass of algae in sealed vats that pumps out hydrogen whenever the sun shines. But the researchers have a few hurdles to overcome. A major problem is the algae are inefficient at capturing sunlight, with 90% of the light falling on them given off as heat or fluorescence. Hankamer and colleagues report they have now used RNA interference (RNAi) to engineer a strain of algae to make the process more efficient. Interestingly, they achieved this by silencing some of the genes responsible for producing light-harvesting The engineered algae only use the light they need rather than wasting it as fluorescence and heat. In a bioreactor this means the light the strain doesn't need would pass through to other light-harvesting algae deep inside the mass. And because the new strain has fewer light-harvesting proteins, it is a lighter green than the natural one, which also helps light to penetrate deeper into the bioreactor. The researchers also say the engineered algae are more resistant to light damage than natural strains. This is important because given the same amount of light, the algae would survive longer and reproduce more, thus possibly generating more hydrogen gas. Hankamer and colleagues have already patented a strain of the algae that is more efficient at converting captured sunlight into hydrogen gas. The next step is to improve the light-capturing efficiency of this strain, says Hankamer. "We have to improve the efficiency of the process in order to make it economically viable," he says. Environmental impacts An algal bioreactor would have obvious positives, says Hankamer. Not only would it produce renewable energy, but he says the algae would also consume more carbon dioxide than they give off. And unlike other biofuel systems, it would not take up valuable arable land, since the bioreactors could be put in desert areas. But what about the environmental negatives? "Nothing is 100% safe, whatever you do. But as far as I can see, this is a very safe system," says Hankamer, who says he has thought very carefully about the safety of genetically modified organisms (GMOs). "I take the concerns of people very seriously who worry about GMOs," he says. The organisms would be unlikely to escape into the environment, he says, because they are in sealed bioreactors and locating these in a desert would provide added safety. "If they escape there they're not going to do much," he says. Finally, he says, the plan is to burn the algal waste using a process called pyrolysis, which sterilises the algae and produces a form of stored carbon called agrichar. The research received Australian Research Council and commercial funding.

Tags: environment, climate-change, biotechnology