Flow cytometry enables dynamic tracking of algal stress response: A case study using carotenogenesis in Dunaliella salina

The cultivation under adverse growth conditions is a commonly used strategy to trigger carotenoid accumulation in microalgae. In order to characterize important factors affecting the biotechnological productivity of microalgal species, systematic and accurate analysis of cellular properties and the physiological response to abiotic stress is required. Therefore, we have investigated the influence of various stress types on a broad spectrum of cellular properties during carotenogenesis in Dunaliella salina in a dynamic manner. Cellular properties were monitored in stained samples for cell vitality and neutral lipid fluorescence together with intrinsic parameters. The results revealed that nitrogen limitation and oversaturating light induced distinct adaptational responses in the cells. In the presence of nitrogen stress, the homogeneous population distribution split into two heterogeneous sub-populations for the cell vitality and neutral lipid fluorescence. Furthermore, we have demonstrated that flow cytometry is able to rapidly detect changes in the cell population upon exposure to abiotic stress. On the basis of this finding, it is possible to determine optimal harvesting time points based on the product content and culture vitality. This enables new perspectives for flow cytometry in the analysis of the metabolic stress response for robust production strategies of microalgal metabolites.