Expression of nitrogen fixation genes only in heterocysts Green cells are heterocysts that are able to fix nitrogen and make hydrogen. Red cells are vegetative cells that cannot fix nitrogen and make hydrogen. Arrows indicate heterocysts identified by brightfield microscopy. Bar=10 M
Nitrogen fixation and hydrogen production in heterocysts
Engineer heterocysts to express an efficient hydrogenase http://www.chemistry.montana.edu/~john.peters/gallery/structure1.html CP1 hydrogenase from Clostridium pasteurianum
Engineer a strain with a very high frequency of heterocysts A high frequency of heterocysts as depicted here (artistic rendering, not actual photo) could allow cultures to produce large amounts of hydrogen using nitrogenase or hydrogenase.
Advantages of Anabaena system Requires only sunlight, air and water to grow and produce hydrogen In contrast to other algal systems, it produces hydrogen in cells growing in air No fossil fuels are required and oxygen is the only byproduct Has been demonstrated to produce ¼ of the volume of a bioreactor of hydrogen per day (Tsygankov, A. A., et al. Biotechnol. Bioeng. 80, 777, 2002)
8 [H + + e - ] Reduces nitrogenase reductase N N Dinitrogenase reduces dinitrogen to ammonia and hydrogen