Optimization of the glycerol production from Dunaliella tertiolecta and Dunaliella isolates

The salt tolerant, marine microalgae Dunaliella tertiolecta is reported to generate significant amounts of intracellular glycerol as an osmoprotectant under high salt conditions. Several studies have identified light color and -intensity, nitrogen- and phosphate limitation, as well as salt concentration as the most inducing factors impacting glycerol productivity. This study aims to optimize glycerol production by investigating these reported factors singularly and in combination to improve the glycerol product titer. The reference strain D. tertiolecta as well as new Dunaliella isolates were evaluated in this study. The results demonstrate that cultivation with white light of an intensity between 500 and 2000 mol m-2 s-1 as opposed to 100 mol m-2 s-1 achieves higher biomass and thereby a higher product titer. Moreover, cultivation in 1.5 M NaCl followed by an increase to 3 M NaCl resulted in hyperosmotic stress conditions, providing the highest glycerol titer. Under these optimal light intensity and salt conditions, the glycerol titer of D. tertiolecta could be doubled to 0.79 mg mL-1. Furthermore, under the same conditions glycerol extracts from new Dunaliella isolates did provide up to 0.94 mg mL-1. Highly pure glycerol obtained under optimal production conditions has widespread applications e.g., in the pharmaceutical industry or the production of sustainable carbon fibers. Moreover, it can be labeled as halal.