The effect of temperature and irradiance on the growth and carotenogenic capacity of seven strains of Dunaliella salina (Chlorophyta) cultivated under laboratory conditions

ABSTRACT

The carotenogenic microalga Dunaliella salina is cultivated as a natural source of ¾ƒ-carotene. The 9-cis isomer of ¾ƒ-carotene is found only in natural sources having commercial advantages over the all-trans isomer due to its high liposolubility and antioxidant power. High irradiance appears to stimulate specifically all-trans ¾ƒ-carotene accumulationin D. salina, whereas low temperature apparently elicits ¾ƒ-carotene and 9-cis ¾ƒ-carotene production. We studied the effect of temperature and irradiance on the growth and the carotenogenesis of three Chilean (CONC-001, CONC-006 and CONC-007) and four non-Chilean (from Mexico, China, Australia and Israel) strains of D. salina cultivated under two photon flux densities (40 and 110 _ 6mol photons.m-2.s-1) and two temperatures (15 and 26ùª C). The Chilean strain CONC-001 and all of the non-Chilean strains exhibited the highest growth rates and the maximum cell densities, whereas the Chilean strains CONC-006 and CONC-007 showed the lowest values in both parameters. The Australian strain showed the highest accumulation of total carotenoids per unit volume (40.7 mg.L-1), whereas the Chilean strains CONC-006 and CONC-007, the only ones isolated from Andean environments, yielded the highest amounts of carotenoids per cell (61.1 and 92.4 pg.cell_1, respectively). Temperature was found to be more effective than irradiance in changing the qualitative and quantitative carotenoids composition. The Chilean strains accumulated 3.5-fold more ¾ƒ-carotene than the non-Chilean strains when exposed to 15ùª C and, unlike the non-Chilean strains, also accumulated this pigment at 26ùª C. The 9-cis/all-trans ¾ƒ-carotene ratio was > 1.0 in all treatments for all strains, and the values were not greatly influenced by either temperature or photon flux density. Physiological and biotechnological implications of these results are discussed.