Heterotrophic growth and nutrient productivities of Tetraselmis chuii using glucose as a carbon source under different C/N ratios

The genus Tetraselmis includes various species that are widely used as food microalgae in aquaculture. However, the mass cultivation of Tetraselmis spp. has been restricted to traditional photoautotrophic culture. Here, we investigated the heterotrophic culture condition for Tetraselmis chuii and assessed growth rate, morphology, and biomass productivity of T. chuii under heterotrophic culture conditions. Protein, polysaccharide, chlorophyll, total lipids, and fatty acid compositions under different initial C/N ratios were also analyzed. Tetraselmis chuii was found to be able to grow using glucose as the sole carbon source under strict heterotrophic conditions. Moreover, T. chuii showed a better heterotrophic growth status in the medium with 10 g L-1 glucose compared to the autotrophic condition. Comparatively high optical density and biomass were obtained at C/N ratios of 16 and 12. The dry weights of T. chuii under C/N ratios of 16 and 12 were 1.37 +/- 0.04 and 1.26 +/- 0.06 mg mL(-1), respectively, significantly higher than those of the autotrophic group. In addition, T. chuii synthesized more polysaccharide under heterotrophic conditions, especially at a C/N ratio of 24. Tetraselmis chuii cultured under C/N ratios of 4 and 8 produced the highest percentages of C16:0 (43.36 %) and C18:1 (47.49 %) fatty acids, and more fatty acids, including C14:0, C18:0, C20:2, and C20:4, were detected in the groups with C/N ratios of 4 and 24. These findings may provide the basis for the mass culture of heterotrophic T. chuii by highlighting sources of plentiful nutrient substances, especially polysaccharides, for aquaculture.