During many millions of years, plants, algae, and cyanobacteria have evolved to oxidize water and generate oxygen. Oxygenic photosynthesis follows the well-established Z-scheme mechanism (Blankenship 2002) wherein photonic energy converts NADP+ to the reductant NADPH and ADP to ATP. These molecules are generated stoichiometrically with photons and are the chemical currencies used to fix CO2 and drive cell metabolism. Fixation of one CO2 requires two NADPH and three ATP. The requirement for CO2 fixation under ABT-737 manufacturer atmospheric conditions (where CO2 concentration is ~0.04%) eFT-508 purchase has been observed to be between 9 and 10 photons/CO2

(Blankenship 2002). The extra photon requirement beyond eight is accounted for by the efficiency loss due to the process of photorespiration. Because of the low-O2/CO2 selectivity of the first enzyme step of carbon fixation, at the ribulose-1,5-bisphosphate carboxylase, oxygenation competes with carboxylation and diverts some carbon to glycolate in systems operating under atmospheric CO2 concentrations. Some phototrophs, particularly C-4 plants and the cyanobacteria, have evolved sophisticated CO2 capture mechanisms to maintain high-CO2 concentrations in physical contact with the carbon-fixing machinery. In photosynthetic processes utilizing CO2 at 50–100 times atmospheric concentrations, it is reasonable SC79 clinical trial to minimize the contribution of photorespiration and to assume photon/CO2

stoichiometries of eight (see

Furbank and Hatch 1987; Zhu et al. 2008). A photon/product ratio can be calculated for any metabolic intermediate or synthetic product from either a natural or engineered recombinantly expressed pathway. Fludarabine manufacturer For example, though fixation of a mole of CO2 into biomass with empirical formula CH2O requires eight photons, production of other metabolic intermediates requiring ATP and/or NADPH may require more photons per mole CO2 fixed. Processes relying on the refining of biomass must account for product yields in efficiency calculations. Algal processes for fuel production take advantage of intrinsically high triglyceride oil production, up to 30–50% dry cell weight (Zemke et al. 2010). Batch cultivation and processing of algae, either in open ponds or in closed photobioreactors, require subsequent harvesting, dewatering, oil processing, and transesterification to produce a biodiesel fuel product, e.g., a fatty acyl ester. The overall productivity of this process is affected by the amount of carbon fixed to triglyceride per unit time and the process efficiency over a given area. This analysis uses the higher yield value for algae. Cyanobacteria, once classified as blue-green algae, are now taxonomically categorized as water-splitting bacteria. They differ from algae in that they lack a defined nucleus and other genome-containing organelle compartments, e.g., mitochondria and chloroplasts, and have bacterial-style inner and outer membranes.