Reconstruction of a genome-scale metabolic model for Auxenochlorella protothecoides to study hydrogen production under anaerobiosis using multiple optimal solutions

Low yield and inhibition of hydrogenase by oxygen are the main limitations for hydrogen production by microalgae. Considering the role of electron flow in the metabolism for hydrogen production, a genome-scale metabolic model (named iMM627) was reconstructed for Auxenochlorella protothecoides. iMM627 was evaluated using experimental data for growth and flux distribution. Then, considering the well-known degeneracy of FBA solutions, a new method of finding effective reactions based on multiple optimal solutions was developed. At a constant growth rate, flux distributions for maximal and minimal hydrogen production under anaerobiosis and for maximal oxygen production were compared to identify target reactions for improvement of hydrogen production and for providing anaerobiosis. Existing researches on some reactions truly confirm the predicted changes by iMM627. The main proposed strategies for improvement of hydrogen production include changes in metabolism to provide NADH. Consumption of oxygen by mitochondrial respiration and energy dissipation was proposed to provide anaerobiosis.