(359e) A Fed-Batch Mixotrophic Cultivation Strategy for Enhanced Biomass Growth and Metabolite Formation

Microalgal biomass - rich in industrially important biomolecules (e.g. carbohydrates, lipids, proteins) - has emerged as a suitable biorefinery platform for high value-added fuels and chemicals [1]. However, despite its promising potential, the large-scale production of microalgae for commercial applications is restricted by the low biomass productivities typically attained by the conventional batch cultivation of phototrophic species (i.e. those that assimilate inorganic carbon dioxide in the presence of light). Low biomass productivities, in turn, lead to a low production of biomolecules, making the overall production and conversion processes economically unattractive [2,3].

Studies have shown that nutrient-limited cultivation influences microalgae’s intracellular composition, generally leading to increased accumulation of intracellular metabolites such as lipids and/or starch. Nevertheless, the benefits of nutrient limitation are often outweighed by a well-known trade-off between metabolite accumulation and cellular growth [4]. Instead, the establishment of a better-suited strategy for induced metabolite formation which does not simultaneously hinder biomass density can be approached through: i) the use of mixotrophic species (i.e. those capable of assimilating both inorganic and organic carbon) which exhibit higher growth rates [5], and ii) fed-batch systems which target prolonged cell life through adequate nutrient feeding regimes [6].

In this work we present a highly productive fed-batch mixotrophic cultivation strategy, consisting of intermittent nutrient pulses, leading to increased biomass growth whilst inducing enhanced metabolite formation. The fed-batch strategy was evaluated at laboratory-scale with the model species Chlamydomonas reinhardtii, grown mixotrophically in standard Tris-Acetate-Phosphate (TAP) medium. Furthermore, an optimal pulse feeding regime (i.e. pulse concentration, pulse feeding time) for maximal metabolite formation, specifically starch and lipid molecules, was identified by exploiting and further enhancing an in-house developed multiparametric kinetic model capable of simulating various fed-batch cultivation scenarios. The optimal pulse-feeding strategy was validated experimentally, and yielded significantly higher concentrations of biomass, starch, and lipids, compared to a typical batch system, making it a promising cultivation strategy fit for biorefinery applications.

References

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