Stress-induced changes in pigment and fatty acid content in the microalga Desmodesmus sp. Isolated from a White Sea hydroid

Effects of light intensity, nitrogen availability, and inoculum density on growth and the content of esterified fatty acids (FA), chlorophylls, and carotenoids in Desmodesmus sp. 3Dp86E-1 chlorophyte alga isolated from the White Sea hydroid Dynamena pumila L. were investigated. The growth of algae in the complete BG-11 medium was not limited by irradiances up to 480 μE/(m² s) PAR but depended on the inoculum density. Under nitrogen starvation conditions, high-intensity light retarded growth of the microalga; this effect was less pronounced in the cultures initiated at high inoculum densities. The highest FA percentage in biomass (30% at the 3rd day of cultivation) was detected in nitrogen-starving cultures grown under high light conditions; however, the highest volumetric FA content (0.25 g/L) was attained on a complete medium at 480 μE/(m² s). An increase in the content of oleic acid (18:1) on the background of a decrease in linolenic acid (18:3) was characteristic of the microalga under stress conditions. The microalga was found to be non-carotenogenic. Nitrogen starvation brought about a dramatic decrease in chlorophyll content on the background of relatively constant carotenoid content. On nitrogen-deplete medium, the high light did not trigger the adaptive response of the pigment apparatus. The changes in absorption spectra of Desmodesmus sp. 3Dp86E-1 cell suspensions reflected the increase in relative contribution of carotenoids to light absorption by the microalgal cells; these changes were tightly related with FA accumulation. The mechanisms of acclimation of Desmodesmus sp. 3Dp86E-1 to high light and nitrogen starvation are discussed in view of possible biotechnological applications of this alga.