Co-cultivation of mixotrophic non-green algae with the green alga Haematococcus pluvialis in aquaculture effluent

Abstract Microalgae cultivation in aquaculture effluents offers an opportunity for high-value biomass production coupled with bioremediation but can be suppressed by bacterial competition. We hypothesized that co-cultivation of Haematococcus pluvialis, known for the synthesis of the valuable carotenoid astaxanthin, with mixotrophic non-green algae could reduce bacterial pressure, leading to enhanced production of algal biomass and nutrient removal. The growth of algae in fourteen two-species co-cultures was screened on 24-well plates, and the best-performing combinations were tested in 650-mL culture bottles in a long-term experiment (28 days) for stability, biomass production, nutrient removal, and biomolecular composition. Contrary to our hypothesis, mixotrophs stimulated bacterial proliferation rather than suppressed it. Co-cultivation reached equal biomass production in comparison to the monoculture of H. pluvialis and frequently improved the nutritional quality of biomass in terms of higher contribution of proteins, total and essential fatty acids (EFAs). However, the highest content of proteins, fatty acids, and EFAs was detected in monocultures of mixotrophs. Particularly Gymnodinium impatiens was rich in EFAs and was successfully cultivated both in mono- and co-cultures for 28 days. Removal of phosphorus and nitrogen by co-cultures was equal to or lower than that by the monoculture of H. pluvialis . Overall, although non-green mixotrophic algae did not decrease bacterial abundance or increase biomass production or nutrient removal, they improved the quality of the produced algal biomass, producing lipid- and protein-rich biomass in aquaculture effluent.