Temperature-salt stress increases yield of valuable metabolites and shelf life of microalgae

Abstract

Background: Microalgae are very important for production of some chemicals industrially, such as carbohydrates, peptides, lipids, and carotenoids. There are many ways by which the yield of the valuable chemicals can be improved. They may include the reduction of cultivation temperature and change in the composition of growth media. Objectives: study adaptive mechanisms of Dunaliella salina Teodoresco and Chlorococcum dissectum Korshikov to low temperature and to develop the method for their hypothermic storage. Materials and methods: The objects of research were unicellular green microalgae D. salina and Ch. dissectum. Cold adaptation (for 24 hours) and hypothermic storage (for 3–30 days) of cultures were performed at 4 °C without lighting. Light and confocal microscopy methods were used to determine the viability and pigment composition of cells. The Alamar Blue (AB) test was used as an express method for assessing the metabolic activity of cells before and after cold adaptation. Results: The study has showed that lowered cultivation temperature and increased salinity of the growth medium increase the fluorescence of the NR dye in D. salina cells and do not affect this indicator in Ch. dissectum. The 24 h exposition at 4 °C does not lead to a significant decrease in the relative fluorescence units according to the AB test. Storage the algae at 4 °C does not result in their loss of viability and motility for up to 30 days. Conclusions: Incubation of D. salina at 4 °C for 24 hours increase carotenoid production compared to the intact culture, while it has no effect on Ch. dissectum, regardless of the growth medium composition. The short-term effect of low temperatures does not lead to a significant decrease in the metabolic activity of D. salina and Ch. dissectum. Storage of museum collection of D. salina and Ch. dissectum is possible for a period of 30 days at 4 °C without significant loss of metabolic activity, motility and cell concentration. These results also demonstrate that a combination of high salt and low temperature stresses increase the yield of valuable metabolites.