CO2 reduction is carbon monoxide (CO), but for fuel development, further reduction is needed, and a key step also needing further development is the transfer of hydride anions to CO. Photobiological production of fuels Some photoautotrophic microorganisms can, under certain conditions, produce hydrogen. Nitrogen-fixing microorganisms, such as filamentous cyanobacteria, possess the enzyme nitrogenase, responsible for conversion of atmospheric N2 into ammonia; molecular hydrogen is a byproduct of this reaction, and is many times not released by the microorganism, but rather taken up by a hydrogen-oxidizing (uptake) hydrogenase. One way of forcing these organisms to produce hydrogen is then to annihilate uptake hydrogenase activity. This has been done on a strain of Nostoc punctiforme: one of the structural genes of the NiFe uptake hydrogenase was inactivated by insertional mutagenesis, and the mutant strain showed hydrogen evolution under illumination. Many of these photoautotrophs also have bidirectional hydrogenases, which can produce hydrogen under certain conditions. However, other energy-demanding metabolic pathways can compete with the necessary electrons for proton reduction, decreasing the efficiency of the overall process; also, these hydrogenases are very sensitive to oxygen. Several carbon-based biofuels have also been produced using cyanobacteria, such as 1-butanol. Synthetic biology techniques are predicted to be useful for this topic. Microbiological and enzymatic engineering have the potential of improving enzyme efficiency and robustness, as well as constructing new biofuel-producing metabolic pathways in photoautotrophs that previously lack them, or improving on the existing ones. Another topic being developed is the optimization of photobioreactors for commercial application. Food production Researchers have achieved controlled growth of diverse foods in the dark . It may become a way to increase energy efficiency of food production and reduce its environmental impacts. However, it is unclear if food production mechanisms based on the experimental process are viable and can be scaled. Employed research techniques Research in artificial photosynthesis is necessarily a multidisciplinary topic, requiring a multitude of different expertise. Some techniques employed in making and investigating catalysts and solar cells include: Organic and inorganic chemical synthesis. Electrochemistry methods, such as photoelectrochemistry, cyclic voltammetry, electrochemical impedance spectroscopy, dielectric spectroscopy and bulk electrolysis. Spectroscopic methods: fast techniques, such as time-resolved spectroscopy and ultrafast laser spectroscopy; magnetic resonance spectroscopies, such as nuclear magnetic resonance, electron paramagnetic resonance; X-ray spectroscopy methods, including x-ray absorption such as XANES and EXAFS, but also x-ray emission. Crystallography. Molecular biology, microbiology and synthetic biology methodologies. Advantages, disadvantages, and efficiency Advantages