Background:Developing algal industries in saline-alkali areas is necessary. However, suitable strains and optimal production conditions must be studied before widespread commercial use.Objectives:The effects of light, temperature, KNO3, and CO(NH2)2 on beta-carotene and biomass accumulation were compared and evaluated in order to provide scientific guidance for commercial algal production in northeastern Thailand.Materials and Methods:An orthogonal design was used for evaluating optimal conditions for the algal production of three candidate Dunaliella salina strains (KU XI, KU 10 and KU 31) which were isolated from saline soils and cultured in the column photobioreactor.Results:The optimal light and temperature for algae growth were 135.3 μmol m-2 s-1 and 22°C, while the conditions of 245.6 μmol m-2 s-1 and 22°C induced the highest level of beta-carotene production (117.99 mg L-1). The optimal concentrations of KNO3, CO(NH2)2, and NaHCO3 for algae growth were 0.5 g L-1, 0.36 g L-1, and 1.5 g L-1, respectively, while 0, 0.12 g L-1 and 1.5 g L-1 were best suited for beta-carotene accumulation. The highest beta-carotene rate per cell appeared with the highest light intensity (12.21 pg) and lowest temperature (12.47 pg), and the lowest total beta-carotene content appeared at the lowest temperature (15°C). There was not a significant difference in biomass accumulation among the three Dunaliella strains; however, the beta-carotene accumulation of KU XI was higher than that of the other two strains.Conclusions:Light and temperature were both relevant factors that contributed to the growth and beta-carotene accumulation of the three D. salina strains, and NaHCO3 had significantly positive effects on growth. The degree of impact of the different factors on cell growth was temperature > NaHCO3 > light intensity > KNO3 > CO (NH2)2 > strains; the impact on beta-carotene accumulation was temperature > light intensity > KNO3 > CO (NH2)2 > strains > NaHCO3

An isolated <em>Dunaliella salina</em> strain from northern Thailand was cultured in modified Johnson’s medium in column photobioreactor. The beta-carotene accumulation mainly depended on the quantities of cells entering into carotenogenesis condition that was significantly enhanced by high started KNO3 concentration. Low remaining nitrate concentration in the culture of each cell (RNCC) was suitable for algae to accumulate beta-carotene. Following the cultivation time extended, RNCC of all cultures decreased and tended to the same level (10-20 pg/cell) although the biomass or betacarotene content in the culture was higher in high started KNO3 concentration. High light intensity restrained the growth especially in low KNO3 concentration but improved betacarotene accumulation and RNCC. The highest biomass and beta-carotene dry weight (DW) were 2.25 g L-1 and 79.2 mg g-1 DW respectively. Above results indicated that increasing the biomass and as early as possible to strengthen the stress on each cell was important to improve the final beta-carotene yield.