The Effect Of Cadimum On Scenedesmus Obliquus And The Optimization Of Culture Conditions For Its Lipid Accumulation

Scenedesmus obliquus is an unicellular green alga that has the advantage of wide spread, rapid growth and easy to cultivate. It is also the ideal raw material for biodiesel due to its high level of neutral lipids in cells. At the same time, it has above 95% adsorption rate for heavy metals, therefore, S. obliquus has the great potential as ideal strains in both energy and environmental fields.The absorption rate of Scenedesmus obliquus on heavy metal cadmium(Cd2+), the photosynthetic activity of S. obliquus under different concentrations of Cd2+ treatment and how to revovery were investigated in this work. The results were the followings:1) The cadmium absorption rate of S. obliquus was up to 97%.2) Half maximal inhibitory concentration (IC50) of Cd2+ was 119.04 μmol/L after 96 h of treatment.3) The concentration of chlorophyll a and photosynthetic activity of S. obliquus were apparently inhibited when the final concentraion of Cd2+ was above 50 umol/L.4) Adding fresh medium failed to restore its photosynthetic activity, moreover, led to the effective PS II quantum yield Y(II) and the maximum PS II quantum yield (Fv/Fm) declined to almost zero. The effect of low Cd2+ concentration (1-10 μmol/L) on S. obliquus was not obvious, and could still maintain a high photosynthetic ability. Considering above results, we preliminary considered that S. obliquus had the potential to act as an ideal adsorption material for cadmium polluted water.Since S. Obliquus has relative higher neutral lipids content in cells. We studied its the neutral lipid content under nitrogen deficiency and sodium tungstate addition conditions, When nitrogen in medium was devoid, the growth and photosynthetic activity of S. Obliquus were limited, while the lipid content has been significantly improved, and the highest lipid content was observed, when nitrogen concentration was 0.176 mmol/L. The lipid fluorescence intensity in cells of S. Obliquus was 40.78 after staining with Nile Red, and corresponding TAG content was 25.2% dry weight.Sodium tungstate as a nitrate reductase inhibitor, can effectively reduce the nitrate reductase activity. The appropriate sodium tungstate concentrations for highest lipid contert in S. Obliquus were studied. The lipid fluorescence intensity in cells was 63.51. when the final concentration of sodium tungstate was 7.5 mmol/L. According to above results, we initially thought that:1) S. Obliquus has the great potential to act as the ideal alga for biofuel and cadmium wastewater treatment.2)"Two-step" method, which was first cultured to a certain biomass then adding sodium tungstate for fatty acid accumulation, not only make the operation easier and make shorter culture period, oil production has been significantly improved, this method for the large-scale cultivation of S. Obliquus biodiesel production provides a theoretical basis.