**4. Conclusions**

We determined that the heterotrophic conditions have several advantages over the autotrophic, such as improving the biochemical composition; enhancing the accumulation of proteins, lipids and carbohydrates and increasing the yield of exopolysaccharides (EPS). The antioxidant activity of the heterotrophic crop was higher with respect to the autotrophic crop, as well as for the algal biomass and EPS. In addition, to the best of our knowledge, this is the first time that autotrophic and heterotrophic EPS of *T. suecica* proved to have cytotoxic effects on HL-60, MCF-7 and NCI-H460 tumor cells. Therefore, they could offer greater benefits as possible natural nutraceuticals for the pharmaceutical industry. More studies are necessary to identify the specific bioactive fractions of each EPS.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/18/11/534/s1: Figure S1–S4: Gas chromatography-mass spectrometry (GC-MS) analysis. Table S1: Pearson correlation between variables from the heterotrophic culture of *T. suecica* (*n* = 3).

**Author Contributions:** Conceptualization, G.P.-R., E.U.-T. and R.T.A-D.; methodology, G.P.-T. and V.C.-A.; software, G.P.-R. and J.G.-M.; validation, G.P.-R., J.G.-.M. and R.T.A-D.; investigation, G.P.-R.; data curation, G.P.-R., J.G.-M. and V.C-.A.; writing—original draft preparation, G.P.-R., J.G.-M. and V.C.-A.; writing—review and editing, G.P.-R., J.G.-M., E.U.-T. and R.T. A.-D.; visualization, G.P.-R., E.U.-T. and R.T.A.-D.; project administration, G.P.-R. and funding acquisition, G.P.-R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the ANID-PFCHA National Doctoral Scholarship, 2018-N◦ 21180059 and FCAC N◦ 057/2019-UCN.

**Acknowledgments:** We want to express our gratitude to the Photobiology and Biotechnology of Aquatic Organisms (FYBOA) research group (RNM-295) for their technical support. We also want to thank the Cell Culture Unit of the SCAI (Central Research Support Service) of the University of Malaga for the technical assistance in the use of the laboratory. We also want to thank the Primary Production Laboratory of the Universidad Catolica del Norte for the use of the laboratory for the development of microalgal cultures.

**Conflicts of Interest:** The authors declare no conflict of interest.
