Researchers have developed a previously undescribed approach to optimize hydrogen production in a photosynthetic process by microorganisms such as algae and cyanobacteria. An open access paper on their work is published in the Proceedings of the National Academy of Sciences.
Although photosynthetic water splitting, coupled to hydrogenase-catalyzed hydrogen production, is considered a promising clean, renewable source of energy, commercialization of this process has been limited because of the oxygen sensitivity of hydrogen production, combined with competition between hydrogen-producing enzymes (hydrogenases) and NADPH-dependent carbon dioxide fixation in the organisms—i.e., for the production of compounds that the organisms use to support their own growth.
Shuguang Zhang, associate director of MIT’s Center for Biomedical Engineering, and postdocs Iftach Yacoby and Sergii Pochekailov, together with colleagues at Tel Aviv University in Israel and the in Colorado, have found a way to use bioengineered proteins to flip this preference, allowing more hydrogen to be produced.
Here we provide evidence that, under the anaerobic conditions that support hydrogen production, there is a significant loss of photosynthetic electrons toward NADPH production in vitro. To elucidate the basis for competition, we bioengineered a ferredoxin-hydrogenase fusion and characterized hydrogen production kinetics in the presence of Fd, ferredoxin:NADP+-oxidoreductase (FNR), and NADP+. Replacing the hydrogenase with a ferredoxin-hydrogenase fusion switched the bias of electron transfer from FNR to hydrogenase and resulted in an increased rate of hydrogen photoproduction. These results suggest a new direction for improvement of biohydrogen production and a means to further resolve the mechanisms that control partitioning of photosynthetic electron transport.—Yacoby et al.
Adding the bioengineered enzyme increases the rate of algal hydrogen production by about 400%, Yacoby says. The sugar production is suppressed but not eliminated, he explains, because “if it went to zero, it would kill the organism.”
|“The algae are really not interested in producing hydrogen, they want to produce sugar.”|
The research demonstrates for the first time how the two processes carried out by algae compete with each other; it also shows how that competition could be modified to favor hydrogen production in a laboratory environment. Zhang and Yacoby plan to continue developing the system to increase its efficiency of hydrogen production.
Ultimately, such a system could be used to produce hydrogen on a large scale using water and sunlight. The hydrogen could be used directly to generate electricity in a fuel cell or to power a vehicle, or could be combined with carbon dioxide to make methane or other fuels in a renewable, carbon-neutral way, the researchers say.
This particular approach, Yacoby says, is simple enough that it has promise “not just in industrialized countries, but in developing countries as well” as a source of inexpensive fuel. The algae needed for the process exist everywhere on Earth, and there are no toxic materials involved in any part of the process, he says.
The work was supported in part by a European Molecular Biology Organization postdoctoral fellowship, the Yang Trust Fund and the US Department of Energy’s National Renewable Energy Laboratory.
Iftach Yacoby, Sergii Pochekailov, Hila Toporik, Maria L. Ghirardi, Paul W. King, and Shuguang Zhang (2011) Photosynthetic electron partitioning between [FeFe]-hydrogenase and ferredoxin:NADP+-oxidoreductase (FNR) enzymes in vitro. PNAS doi: 10.1073/pnas.1103659108