Two Different Strains Of Dunaliella Salina Optimization Of Culture Conditions And The Accumulation Of ?-carotene

Dunaliella salina is a single-celled microalgae with photoautotrophic and halophilic properties.The cell has non-cellulosic cell wall,and can synthesize and accumulate high levels of P-carotene,oil,protein and polysaccharose,showing particular values in food,medicine and health care,chemical engineering,and animal husbandry.Using Dunaliella salina to service as a platform for commercial production of natural ?-carotene is being developed as new industry of functional agriculture.In order to establish a large-scale and high-efficient cultivation system for obtaining high biomass of Dunaliella salina and ?-carotene yield,the current study was conducted to optimize culture conditions for two strains of Dunaliella different in physiological characters,and to deeply analyze the mechanism of ?-carotene accumulation in their cells under different stress conditions.The main results were described as the followings.(1)We isolated and purified a new strain of Dunaliella salina Ds-SXYC-1 enriched in?-carotene from the microalgae samples collected from Yuncheng Salt Lake,Shanxi Province,China.Another high(3-carotene Dunaliella strain 558 was bought from Institute of Hydrobiology,Chinese Academy of Sciences.Physiological analysis indicated that these two stains were different in some traits.(2)We measured and analyzed the traits of these two strains,including cell growing rate,cell morphology,physiological and biochemical changes as well as target product accumulation by cultivating them in different salt concentration,light intensity and pH conditions.Finally,after comprehensive evaluation,we established the optimal culture conditions and parameters of these two strains.In particular,the optimal culture conditions of Dunaliella salina Ds-SXYC-1 from Yuncheng Salt Lake were as follows:salt concentration:0.5 mol/L,pH:5.5-6.5,and light intensity:5000 lux.While,the optimal culture conditions ofDunaliella strain 558 were following:salt concentration:1.5 mol/L,pH:7.5,and light intensity:5000-6500 lux.(3)First,we used ultraviolet spectrophotometer to scan full wavelength of Dunaliella salina and ?-carotene respectively,and got the results that the best part of Dunaliella salina to absorb wavelength was 684 nm,while that of ?-carotene to absorb wavelength was 453nm.Then,we gained linear relationship between ?-carotene absorbance and the weight by using acetone-petroleum ether method to draw ?-carotene standard curve,which could facilitate us to monitor cell biomass and ?-carotene accumulation dramatically.(4)We used the optimal culture conditions set above to cultivate these two strains in large-scale,and then tested the biomass of microalgae samples and ?-carotene in different stages.According to the date,we found that under the optimal culture conditions,the?-carotene of Dunaliella salina Ds-SXYC-1(2.3%)from Yuncheng Salt Lake was better than that of Dunaliella strain 558(1.5%),while the cell biomass,which was 0.098 g/L/d,was less than Dunaliella strain 558(0.201g/L/d).(5)We also cultivated these two strains massively in high and low light,salt,and temperature stress conditions,in order to gain the content of ?-carotene,as well as to measure the rate of ?-carotene and dry cell weight.The result showed that both these two Dunaliella strain could be accelerated to accumulate ?-carotene in the condition of high light,salt,and temperature,but the effect was different.The ?-carotene accumulation of Dunaliella salina Ds-SXYC-1 from Yuncheng Salt Lake was higher than that of Dunaliella strain 558 obviously.Apart from that,we also found that high temperature was not good for Dunaliella strain 558 to grow.Once it exposed in high temperature too long,it was likely to die.On the contrary,the condition with low light,salt and temperature had no remarkable effect on the?-carotene accumulation of these two strains.Finally,according to the result,Dunaliella salina Ds-SXYC-1from Yuncheng Salt Lake is an excellent strain of microalgae which can produce ?-carotene large-scale.Besides,the established optimum cultivating condition and parameter can serve for establishing a large-scale and high-efficient cultivation system and production of natural(3-carotene.