Salinity and nitrate concentration on the growth and carotenoids accumulation in a strain of Dunaliella salina (Chlorophyta) cultivated under laboratory conditions

1 - The effect of salinity (9, 14, and 22 % NaCl w/v) and nitrate concentration (882, 435 and 212 ìmol L-1) on the growth and production of carotenoids was studied in a wild strain of Dunaliella salina Teod. isolated from solar salterns on the Tyrrhenian coast (Tarquinia – Central Italy). 2 - The alga was grown in batch culture at relatively low illumination (40 ìmol photon m-2s-1). The total content of carotenoids produced from the alga and the amount of all-trans-â-carotene, the isomer showing a relevant commercial value, were determined by UV-Vis spectrophotometry and HPLC analysis. 3 - The highest growth rate in this strain of D. salina was obtained at salinity of 22% NaCl w/v and elevated nitrate concentration (882 ìmol L-1); a relatively high cell density was also observed at higher salinity and reduced nitrate concentrations. Low nitrate concentration negatively affected growth, but enhanced the carotenoids accumulation in the cells. 4 - The highest concentration of carotenoids (17 pg/cell) was observed in the 28 day old cultures in the late stationary phase at 22% NaCl w/v and 212 ìmol L-1 nitrate concentration. Also the average of all-trans-â-carotene on total carotenoids was enhanced by low nitrate concentration changing from 5% in 28 day old cultures at 22% salinity and 882 ìmol L-1 N, to 37% in 28 day old cultures at 22% NaCl w/v and lower nitrate concentration (212 ìmol L-1)