Enhanced β-carotene and Biomass Production by Induced Mixotrophy in Dunaliella salina across a Combined Strategy of Glycerol, Salinity, and Light

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and beta-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 mu mol photons m(-2) s(-1) light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 x 10(6) cell mL(-1)) and beta-carotene accumulation (4.43 pg cell(-1)). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 mu mol photons m(-2) s(-1)) caused the beta-carotene to reach values higher than 30 pg cell(-1) and tripled the beta-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal beta-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and beta-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.

Automated summary

Optimizing the mixotrophic conditions with glycerol, salinity, and light intensity can significantly enhance the growth and beta-carotene yields of Dunaliella salina. Increasing light intensity and non-isosmotic salinity can further improve beta-carotene productivity in the microalga.