Biological Sciences

NREL researchers in the Biological Sciences group are helping the nation develop environmentally benign technologies that will produce renewable fuels and chemicals in the near future. Our work emphasizes the biochemistry, physiology, and molecular biology of algae, cyanobacteria, photosynthetic bacteria, and dark fermentative bacteria. This research is revealing new ways to produce hydrogen fuel and valuable reduced-carbon byproducts. The common theme is to understand and manipulate normal photosynthesis and dark fermentation. The former can use sunlight to split water and the latter uses waste biomass. Both processes will produce desirable products.

The major research activities of the Biological Sciences group involve:

• Basic Studies of Photosynthesis
• Basic Studies of Hydrogenases
• Microbial Hydrogen Production by Direct Conversion Processes
• Fermentative Hydrogen Production

Basic Studies of Photosynthesis

The process of plant photosynthesis produces the oxygen we breathe, the food we eat, and important materials for our homes, clothes, and industries. NREL researchers are seeking to understand the detailed workings of the part of the photosynthetic apparatus that provides the energy and electrons that plants require to grow. These particular processes lead to the splitting of water molecules and the evolution of oxygen (which, to the plant, is a waste product). Our research has "visualized" the protein structure that performs these basic processes and has examined the extremely fast photochemical reactions (in trillionths of a second!) that drive these processes. Furthermore, the specific structure and function of the protein complex that actually splits water is under examination. New understanding may someday help us improve the efficiency of natural photosynthesis and design artificial photosynthetic processes as next-generation systems to produce renewable energy.

Basic Studies of Hydrogenases

Hydrogenases are specialized proteins (enzymes) that can take electrons released from water by photosynthesis and combine them with protons also released by the water-splitting process. The result is the generation of hydrogen gas. NREL is studying the basic structure of hydrogenases at the molecular level in order to understand the mechanisms involved in the generation of hydrogen, and how the enzymes can be modified to improve the efficiency and duration of hydrogen production in vivo (within a living organism) or coupled to synthetic photochemical cells. Our work also involves studies of the factors that affect the expression of hydrogenase genes, such as the redox (reduction of oxidation) state of the cells and the activity of the accessory proteins that perform the assembly of the metallo-catalytic clusters of hydrogenases.

Microbial Hydrogen Production by Direct Conversion Processes

Green algae and cyanobacteria can produce hydrogen by splitting water through a process called "biophotolysis" or "photobiological hydrogen production." This photosynthetic pathway produces renewable fuels without producing greenhouse gases. The scientific challenge associated with the approach is that the hydrogenase enzyme is sensitive to oxygen. The process of photosynthesis produces oxygen, but this normally stops hydrogen production very quickly in green algae. To overcome this problem, NREL scientists are trying several approaches. First, oxygen and hydrogen production in algae are separated from each other using a nutrient stress mechanism. Second, oxygen-tolerant bacterial hydrogenases are being introduced into cyanobacteria so that the organisms can produce hydrogen when some oxygen is present. Finally, hydrogenases in the green alga, Chlamydomonas reinhardtii, are being engineered to remove the detrimental oxygen-sensitivity property. The ultimate goal of this work is to develop a water-splitting process that will result in a commercial hydrogen-production system that is cost effective, scalable to large production, non-polluting, and self-sustaining.

Fermentative Hydrogen Production

Another attractive feedstock for hydrogen production is waste lignocellulosic biomass (the leafy or woody part of plants). Two challenges must be overcome: the high cost of glucose feedstock and the low yield of hydrogen. To lower the cost of the feedstock, NREL scientists have identified cellulolytic bacteria such as Clostridium thermocellum, which can use cellulose and hemicellulose directly for hydrogen production. To overcome the relatively low yield of hydrogen production from sugar metabolism, NREL scientists will metabolically engineer the organism to divert cellular energy toward hydrogen production while minimizing the accumulation of other waste metabolites. Surmounting this technical barrier will maximize the potential of fermentative hydrogen production.

For staff profiles, publications, and contact information see Biological Sciences Research staff.