Photosynthesis from a hydrogen-producing, single-celled green alga, Chlamydomonas reinhardtii, has unmasked a previously unknown fermentation pathway that may open up possibilities for increasing hydrogen production.

Alexandra Dubini and Michael Seibert from the National Renewable Energy Laboratory, Florence Mus and Arthur Grossman of the Carnegie Institution’s Department of Plant Biology, and Matthew Posewitz from the Colorado School of Mines have a new study out published in the Journal of Biological Chemistry.

Chlamydomonas reinhardtii is a common inhabitant of soils that naturally produces small quantities of hydrogen when it’s deprived of oxygen. When starved of oxygen this particular alga generates its energy from fermentation like yeast and other microbes. While fermenting, the hydrogen is released though the action of an enzyme called hydrogenase, powered by electrons generated by either the breakdown of organic compounds or the splitting of water by photosynthesis. Usually, only a small fraction of the electrons go into generating hydrogen. The major research goal is to develop ways to increase this fraction, which would raise the potential yield of hydrogen.

The research group examined the metabolic processes in a mutant strain of Chlamydomonas reinhardtii that was unable to assemble an active hydrogenase enzyme. They expected the cell’s metabolism to compensate by increasing metabolite flow along other known fermentation pathways, such as those producing formate and ethanol as end products. Instead, the algae activated a pathway leading to the production of succinate, which was previously not associated with fermentation metabolism in the specimen.

Now that the team has fully sequenced the Chlamydomonas genome, researchers can identify key genes encoding proteins involved in both fermentation and hydrogen production.

Grossman feels that it is of immediate importance to generate new mutant strains to help us understand how we may be able to alter fermentation metabolism and the production of hydrogen. NREL’s Michael Seibert, the project’s Principal Investigator, observed that “the overarching goal of the work is to gain a fundamental understanding of the total suite of metabolic processes occurring in Chlamydomonas and how they interact; this discovery effort will lead to the development of novel ways to produce renewable hydrogen and other biofuels, which will benefit all of us”.

Grossman says, “We actually didn’t know that this particular pathway for fermentation metabolism existed in the alga until we generated the mutant. This finding suggests that there is significant flexibility in the ways that soil-dwelling green algae can metabolize carbon under anaerobic conditions. By blocking and modifying some of these metabolic pathways, we may be able to augment the donation of electrons to hydrogenase under anaerobic conditions and produce elevated levels of hydrogen.”

Posewitz says, “These are really exciting times in the field. The tools developed at Carnegie and by other groups in the field are presenting unprecedented opportunities for scientists to make important advances in our understanding of the basic biology of organisms such as Chlamydomonas.”

Hydrogen is a commonly needed element in producing a wide array of products in addition to the popular idea to use it to replace fossil fuels. Algae as a biological source of hydrogen production would offer a non fossil fuel source. Algae sourced production would likely not need agricultural land.

But there is a very long way to go. The research in the algae to hydrogen field is just now getting results. Yet should an algae hydrogen process become commercial the ability to use it in carbon fuel products would dramatically change the ways carbon that’s hydrogen enriched would come to market. It also adds another reason to research the algae family for more resources in biological processes to fuels.


3 Comments so far

  1. Matt on March 27, 2009 6:15 AM

    Unfortunately, purity is the problem. Anyone who lives close to a hog farm can attest to natures ability to product hydrogen. (Hydrogen sulfate is what smells so bad) But, the impurities foul up fuel cells like bad gas in an automobile engine.

    I don’t believe algae will ever be able to produce a pure enough hydrogen for commercial use.

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