Influence of culture medium recycling on the growth of a marine dinoflagellate microalga and bioactives production in a raceway photobioreactor

Abstract Amphidinium carterae is a marine dinoflagellate microalga that produces high-value bioactive polyketides such as amphidinols and amphidinolides, which have remarkable cytotoxic, antifungal and antitumoral activities. This species also produces docosahexaenoic acid and the carotenoid peridinin as high-value byproducts. The development of any sustainable microalgae-based bioprocess must comprise complete valorization of the biomass and reuse of the exhausted culture medium as much as possible to comply with the circular economy concept. In this work we have assessed the effect of recycling the cell-free supernatant on the growth kinetics and production of amphidinols by A. carterae photoautotrophically cultured in a pilot-scale raceway-type photobioreactor in semi-continuous mode. Acclimation to the recycled medium was first studied on a laboratory scale and was accomplished in the fourth sub-culture, except for pigment content, which decreased throughout the process. No measurably negative effect was detected in the cells. Maximum growth rates and cell productivities increased by 60% with use of 75% spent medium, as a result of mixotrophic consumption of the organic carbon present in that medium, remaining constant thereafter. In the photobioreactor, acclimation took 77 days and was also accomplished in the fourth sub-culture, with no negative effects on cell health. Biomass and cell productivities were higher with the recycled medium than with the fresh medium. Pigments decreased throughout the acclimation process, probably due to organic carbon-based mixotrophic growth. Amphidinols and docosahexaenoic acid biomass contents were not affected by medium recycling, which will significantly improve the economics of amphidinols production from A. carterae cultures on a circular economy basis.