Screening Of Oil-Rich Marine Microalgae And The Effect Of Nutritional Conditions On The Growth And Lipid Accumulation Of It

With the rapid development of the global economy, non-renewable fossil fuels are overexploited, leading to a worldwide increasingly shortage of energy. Biodiesel is a renewable and ecologically friendly energy resource, and the development of it becomes increasingly important and is attractive to the researchers of the world.Microalgae are of particular interest as a most promising source of biomass for biodiesel production due to their rapid growth rate, short growth cycle, high lipid content, strong adaptability to environment and easy to cultivation and so on. However, the production of biodiesel from microalgae is still too expensive to meet the market requirements. To solve this problem, it is essential to identify suitable strains of microalgae for mass cultivation and improve the lipid content of them.In this study, we isolated and purified marine microalgae from natural seawater and identified them by their morphology. Oil-rich marine microalgea was screened from microalgal species of our laboratory and the marine microalgae we isolated. The lipid productivity of Chlorella sp. NJ101was the highest, so the effects of nutrient conditions on the growth and lipid accumulation of Chlorella sp. were explored. Nutrient deprivation was used to enhance the lipid content of marine microalgae. The main results are as follows:(1) Two marine microalgae were isolated and purified form natural seawater. One of them was green alga which was identified as Chlorella sp. NJ101and the other was diatom which was identified as Nitzschia closterium f. minutissima NJ112. Three marine microalgae with faster growth, higher biomass productivity and higher lipid productivity were screened out from the ten strains; they are Chlorella sp. NJ101, Chaetoceros muelleri and Dunqliella salina. The saturated and monounsaturated fatty acids content of Chlorella sp. NJ101and Chaetoceros muelleri were more than80%and that of Dunaliella salina even more than90%. The growth rate of Chlorella sp. NJ101was the faster and the biomass productivity and the lipid productivity of Chlorella sp. NJ101was the highest and the fatty acid composition of Chlorella sp. NJ101meets the requirement of EN14214, so, Chlorella sp. NJ101was a promising biodiesel feedstock.(2) When NaHCO3, Na2CO3and glucose were added to the medium as carbon source, the biomass productivity and lipid productivity of Chlorella sp. NJ101was reduced. The highest biomass productivity and lipid productivity of Chlorella sp. NJ101was obtained when NaNO3was used as nitrogen source. So, when Chlorella sp. NJ101was used to produce biodiesel, NaNO3was more suitable to use as the nitrogen source than NH4CI and CO(NH2)2. NaNO3and NaH2PO4have a great influence on the biomass productivity and lipid productivity of Chlorella sp. NJ101. The most significant effect on the lipid productivity of Chlorella sp. NJ101was obtained when the concentrations of NaNO3were between2.2-8.8×10-3mol·L-1or the concentration of NaH2PO4were between1.8×10-5mol·L-1-1.8x10-4mol·L-1. Different concentration of Na2SiO4didn’t have significant effect on the biomass productivity and lipid productivity of Chlorella sp. NJ101. None of the addition or the concentration of MgSO4had significant effect on the growth and lipid productivity of Chlorella sp. NJ101. When CaCl was supplemented to the medium of Chlorella sp. NJ101, the biomass productivity was increased though not significant, and the lipid productivity was significantly increased with suitable CaCl concentration.(3) The addition of FeCl3significantly increased the lipid productivity of Chlorella sp. NJ101, but the concentration of FeCl3didn’t have significant effect on the lipid productivity of Chlorella sp. NJ101. None of the addition or the concentration of CuSO4, Na2Mo04, ZnSO4, CoCl2and MnCl2had significant effect on the growth and lipid productivity of Chlorella sp. NJ101.(4) The optimum nutrients concentration with which the lipid productivity of Chlorella sp. NJ101was highest was obtained form the orthogonal experiment:NaNO3-N8.8×10-4mol·L-1; NaH2PO4-P7.2×10-5mol·L-1; FeCl3-Fe0.5×10-5mol·L-1. And the fatty acid composition of Chlorella sp. NJ101in all the trials meets the requirement of EN14214.(5) Complete nutrition deprivation resulted in the largest reduction of C. muelleri, D. salina and Chlorella sp. NJ101growth, followed by deprivation of nitrogen, phosphate and iron from the medium. Deprivation of nitrogen gave the greatest physiological stress to C. muelleri and Chlorella sp. NJ101, followed closely by deprivation of complete nutrient, phosphate and iron. Complete nutrition deprivation gave the greatest physiological stress to D. salina, followed closely by deprivation of nitrogen, phosphate and iron. The highest lipid content for C. muelleri was achieved by nitrogen deprivation and the lipid content were46%of dry cell weight. The highest lipid content for D. salina and Chlorella sp. NJ101was achieved by complete nutrient deprivation, and the lipid content were54%and64%of dry cell weight, respectively. It means that Chlorella sp. NJ101isolated form seawater has the highest lipid content when the nutrient deprivation was used.In short, one microalge with high lipid productivity was screened form natural seawater; it is Chlorella sp. NJ101. The effects of different nutrient conditions on the growth and lipid accumulation of Chlorella sp. NJ101were studied. Nutrient deprivation was used to enhance the lipid content of marine micoalgae with high lipid productivity. This article provides a theoretical and experimental basis to the further development of microalge biofuel and the enhancement of microalgal lipid content and will speed up the commercialization of microalgae biodiesel.