Screening and lipid analyses of high oleaginous Chlorella species.

Chlorella species which have strong adaptability distributes widely in various habitats,especially in the freshwater.Their assimilation product is mainly starch,but environmental stress can trigger lipid accumulation within the cells.The predominant fatty acids are C16 and C18 in Chlorella species,which are suitable feedstocks for biodiesel production.A number of Chlorella strains were isolated from fresh water of China,and their triacylglycerol contents were analyzed by thin layer chromatography.Out of 21 oleaginous Chlorella strains,a high oleaginous stain,NMX37N,was identified.It grew at temperatures from 15 to 35 ℃ but not at 40 ℃,and the optimum conditions,at 25 ℃ and 250 μmol photons/m2.s,it grew with a specific growth rate of 0.53/d.Batch culture experiments showed that the content of triacylglycerols in Chlorella sp.NMX37N increased with time and reached to the highest at the late stationary phase when the nitrate was exhausted.The total lipid content was 33% of dry cell weight when Chlorella sp.NMX37N grew under batch culture conditions for 40d.A two-step culture method,namely,transfer to the nitrogen deficiency condition at the late exponential phase(about 20d),gave a higher total lipid(36%) compared with the batch culture method.The main fatty acids(70%) in total lipids and triacylglycerols of Chlorella sp.NMX37N were C16∶0 and C18∶2.In addition,there were no long-chain fatty acids,such as C20,in Chlorella sp.NMX37N.The results indicated that the triacylglycerols in Chlorella sp.NMX37N may serve as excellent feedstocks for biodiesel production.