Characterization of Dunaliella salina strains by flow cytometry: a new approach to select carotenoid hyperproducing strains

In the present work the characterization of different strains of Dunaliella salina from established cell culture collections and various isolates from solar saltworks located in the Canary Island, as well as one mutant, was carried out in order to assess the existence of intraspecific differences and to determine the potential productivity of each one. Morphological characteristics such as cellular size and cellular complexity and parameters linked to cellular physiology, such as pigment content or cellular growth rate, were determined by means of traditional techniques as well as flow cytometry. Results showed a high morphological and physiological intraspecific variability among the studied strains. Results suggest that the application of the lipidic dye Nile red allowed the development of a cytometric method faster than the traditional techniques to select carotenoid hyperproducing strains of microalgae.

Nutrient limitation is the main regulatory factor for carotenoid accumulation and for Psy and Pds steady state transcript levels in Dunaliella salina (Chlorophyta) exposed to high light and salt stress.

Dunaliella salina (Dunal) Teodoresco (1905) is a green unicellular alga able to withstand severe salt, light, and nutrient stress, adaptations necessary to grow in harsh environments such as salt ponds. In response to such growth conditions, this microalga accumulates high amounts of beta-carotene in its single chloroplast. In this study, we show that carotenoid accumulation is consistently inhibited in cells grown in nutrient-supplemented media and exposed either to high-light or medium-low-light conditions. Likewise, carotenogenesis in cells shifted to higher salinity (up to 27% NaCl) under medium-low-light conditions is inhibited by the presence of nutrients. The steady-state levels of transcripts encoding phytoene synthase and phytoene desaturase increased substantially in D. salina cells shifted to high light or high salt under nutrient-limiting conditions, whereas the presence of nutrients inhibited this response. The regulatory effect of nutrient availability on the accumulation of carotenoids and messenger RNA levels of the first two enzymes committed to carotenoid biosynthesis is discussed.