A fluxomic model of microalgae photoautotrophic growth for application in industrial photobioreactors

In commercial microalgae cultivations with high cell density, individual cells are exposed to rapid shifts in the illumination conditions, due to a limited light penetration combined with the fluid circulation patterns. The impact of these shifts on the physiological state of the cells must be precisely assessed, to obtain reliable predictions of the productivity of the cultivation, and to evaluate the degree of light utilization and the illumination needs. To this end, in this study we present a first-principles dynamic model that encompasses the processes of photon capture, electron transport, photoinhibition, pH regulation and carbon fixation, at the molecular level. These processes are characterized in terms of several cellular rates, including electron transport, photodamage, photorespiration, pH variation in stroma and lumen, ATP and NADPH formation and consumption, carbon fixation, and O 2 and CO 2 exchange across the cell membrane. The rates, grounded it a state-of-the-art understanding of the photosynthetic machinery in the chloroplast, are incorporated into a system of 10 differential equations, which yields macroscopic predictions of oxygen production, carbon consumption and biomass growth rate. The computational simulation showed results in significant agreement with multiple literature sources, thereby validating the mechanistic modelling framework. The resulting model, based on a characterization of fundamental photosynthetic components, is therefore broadly applicable, and can be adapted to different microalgae species. • A dynamic mechanistic model for photosynthesis-associated processes has been developed. • The model encompasses photon capture, electron transport, photoinhibition, pH regulation and carbon fixation. • Literature-based parametrization led to results in good agreement with available empirical data.