Metabolic modeling of C. sorokiniana diauxic heterotrophic growth

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Abstract: Microalgae are promising microorganisms for the production of numerous molecules of interest, such as pigments, proteins or triglycerides that can be turned into biofuels. Heterotrophic growth on wastes represents an interesting approach to achieve higher biomass concentrations, while reducing cost and improving the environmental footprint. Wastes generally consist of a mixt of diverse molecules. It is crucial to understand microalgal metabolism in such conditions, where switching between substrates might occur. Metabolic modeling has proven to be an efficient tool for understanding metabolism and guiding the optimization of biomass or target molecule production. Here, we focused on the metabolism of Chlorella sorokiniana growing heterotrophically on acetate and butyrate. The metabolism was represented by 163 metabolic reactions. The DRUM modeling framework, with a mildly relaxed quasi-steady-state assumption, was used to account for possible intracellular accumulation during switching between substrates. Six experiments were used to calibrate the model and eight experiments for the validation. The model efficiently predicted the experimental data, including the transient behavior. To the best of our knowledge, this is the first study to describe the dynamic metabolic fluxes of microalgae during heterotrophic and diauxic growth. It shows that an accurate model of metabolism can now be constructed, even in dynamic conditions, with the presence of several carbon substrates. It also opens new perspectives for the heterotrophic use of microalgae, especially for biofuel production from wastes.