Bioactives Overproduction through Operational Strategies in the Ichthyotoxic Microalga Heterosigma akashiwo Culture

The red tide-forming microalga Heterosigma akashiwo has been associated with massive events of fish deaths, both wild and cultured. Culture conditions are responsible for the synthesis or accumulation of some metabolites with different interesting bioactivities. H. akashiwo LC269919 strain was grown in a 10 L bubble column photobioreactor artificially illuminated with multi-coloured LED lights. Growth and production of exopolysaccharides, polyunsaturated fatty acids (PUFAs), and carotenoids were evaluated under different culture modes (batch, fed-batch, semicontinuous, and continuous) at two irradiance levels (300 and 700 mu E (.)s(-1.)m(-2)). Continuous mode at the dilution rate of 0.2(.)day(-1) and 700 mu E(.)s(-1.)m(-) (2) provided the highest production of biomass, PUFAs (132.6 and 2.3 mg(.)L (-1) (.)day(-1)), and maximum fucoxanthin productivity (0.16 mg(.)L(-1.)day(-1)). The fed-batch mode accumulated exopolysaccharides in a concentration (1.02 g(.)L(-1)) 10-fold over the batch mode. An extraction process based on a sequential gradient partition with water and four water-immiscible organic solvents allowed the isolation of bioactive fucoxanthin from methanolic extracts of H. akashiwo. Metabolites present in H. akashiwo, fucoxanthin and polar lipids (i.e., eicosapentaenoic acid (EPA)), or probably such as phytosterol (fi-Sitosterol) from other microalgae, were responsible for the antitumor activity obtained.

Automated summary

The red tide-forming microalga Heterosigma akashiwo is linked to significant fish mortality events. Different culture conditions can affect the production of metabolites with unique bioactivities. A study investigated the growth and production of H. akashiwo LC269919 strain in a 10 L photobioreactor under various culture modes and irradiance levels. Continuous mode at a dilution rate of 0.2 day-1 and 700 mu E.s-1.m-2 provided the highest production of biomass, PUFAs, and fucoxanthin.