Evaluation of C/N ratios (glucose/nitrate) for heterotrophic cultivation of a Brazilian strain of Tetradesmus obliquus: An assessment of heterotrophic, mixotrophic, and photoautotrophic conditions

The growth of microalgae under different trophic modes is widely considered in the literature. However, the cultivation of some microalgal strains under heterotrophic conditions requires further investigation. Thus, the present study investigated the growth potential of a Brazilian strain of Tetradesmus obliquus (Chlorophyceae, Scenedesmaceae) in terms of heterotrophic metabolism. For this purpose, cultures were generated using different concentrations of glucose (26, 13, and 6.5 g L^–1) and sodium nitrate (0.6 g, 0.3, and 0.15 g L^–1) in culture media. The growth parameters analysed were the maximum biomass achieved and volumetric productivity. The combination of 26 g L^–1 glucose with 0.6 g L^–1 sodium nitrate resulted in the greatest increase in dry weight (9.63 ± 0.15 g L^–1). Then, T. obliquus cultures under heterotrophic conditions were compared with those under photoautotrophic and mixotrophic conditions. The maximum production in heterotrophic cultivation was similar to what had been obtained, while mixotrophic cultivation presented the best result, 14.77 ± 0.06 g L^–1, and photoautotrophic cultivation obtained a maximum biomass of 7.90 ± 0.17 g L^–1. The productivity values achieved were 0.52 ± 0.04 g L^–1 day^–1, 0.98 ± 0.07 g L^–1 day^–1, and 1.24 ± 0.07 g L^–1 day^–1 for photoautotrophic, heterotrophic and mixotrophic cultures, respectively. The results indicated that the Brazilian microalga T. obliquus has the potential to be successfully cultivated heterotrophically.