Studies On High-concentration Cultivation And Se-Bioaccumulation Of Spirulina Maxima

Spirulina is rich in protein and contains various bioactive substances, and has broad application prospects in food, medical health, feeding, fine chemical industry and cosmetic industry etc. In the present thesis, Spirulina maxima was mixtrophic cultured as the research object by adding organic compounds into the medium using the photo bioreactor. In this way, the limitation of light intensity to the growth of Spirulina decreased and the cost could reduce, the high-concentration of Spirulina was finally implemented. In addition,in order to enhance the biomass and the organic-Se content of S.maxima, the conditions of Se-bioaccumulation in S.maxima was optimized.In order to realize high concentration culture, the following experiments needed to be done. Firstly, the concentrations of some nutrient elements in the Zarrouk medium were optimized, containing carbon source, nitrogen source and some inorganic ions, and the effects of temperature ,initial pH and light intensity on Spirulina maxima were studied. The best concentrations of the chosen factors in Zarrouk medium were as follows: NaHCO₃ 16.8g/L,NaNO₃ 2.0 g/L,NaCl 2.0g/L,MgSO₄·7H₂O 0.1 g/L,K₂SO₄ 2.0 g/L,K₂HPO₄·3H₂O 0.6 g/L.And suitable growth conditions for S.maxima were as follows: light intensity 3500 lx, temperature 30℃, initial pH 9.3. Secondly,mixtrophic culture was carried out by adding organic carbon and nitrogen sources into the optimum medium. The organic carbon and nitrogen sources that could promote the growth of S.maxim were chosen from different organic substance. The best proportion of inorganic and organic carbon and nitrogen sources was confirmed by orthogonal experiment. The results showed: S.maxima was cultivated in the medium with peptone 0.4g/L, glucose 1.5g/L, NaHCO₃ 16.8g/L, NaNO3 2.5g/L under 3500lx,and the highest biomass of S.maxima was 3.73g/L. Finally, the high-concentration cultivation of S.maxima was implemented in the photo bioreactor. The culture conditions were confirmed as follows: light intensity 3000lx, ventilation volume 120L/h(0.5vvm),temperature 30℃,stirring speed from the beginning of 150r/min and progressive increased with 10r/min per day,the glucose was flow feeding at the 4th day and the concentration was maintained at 2.0g/L after feeding per day. The S.maxima was cultivated for 10 days in this way and the final biomass was 3.06g/L。The light intensity of 3000lx became the critical factor that limited the growth of S.maxima because of light attenuation in the photo bioreactor. In this condition, The flow feed of high-concentration medium and NaHCO3 made the opposite effects on the accumulation of S.maxima biomass. However, the flow feed of glucose–a organic carbon source could weaken the dependence of S.maxima on the light and enhance the yield of S.maxima effectively.Physical and nutrient factors that affect the growth and Se-enrichment of S .maxima were studied systematically, including Se(IV) concentration , adding measures for Se(IV), light intensity , initial pH, carbon sources and nitrogen source. Finally, the optimal cultivation conditions were confirmed as: the total Se adding concentration was 800μg/mL Se(IV), which was added multi-time equivalently daily in eight days, light intensity 2000Lx:5000Lx = 12h :12h , pH 9.8, NaHCO₃ 12.8g/L and NaNO3 2.5 g/L. The response results was biomass concentration at 2.517g/L and total Se content at 2.843 mg/g md,the proportion of organic selenium was above 95%,the effectiveness of selenium enrichment was great improved.