Optimization Of Culture Conditions For Oil Production Of Phaeodactylum Tricornutum And Analysis Of Active Substances In The Cells

Culture conditions of oil-enriching algae, Phaeodactylum tricornutum were optimized inflat plate photobioreactors. The differences of the growth kinetics curve, specific growth ratesand biomasses under the culture conditions of different light paths of reactors, salinities,nitrogen concentrations, and temperatures were compared by using single factor experiment.Products, harvested from the stationary phase culture under different culture conditions, wereanalyzed on the contents of lipid, soluble protein and polysaccharide. Lipid productivitieswere calculated from the algal cell biomass and lipid content. Orthogonal experiments weredesigned and carried out for optimization of the culture conditions of Phaeodactylumtricornutum.With the increase of the light path of reactors the cell density, specific growth rate,biomass and volumetric productivity decreased, the areal productivity increased. Algal cellscultured in narrow light path reactors conducive to the accumulation of lipid. The biomassesand lipid content of5cm light path culture was obviously higher than that of other cultures,reached1.82g/L and31.54%respectively. Thus, the volumetric productivity of lipid was verymarkedly higher than that of other cultures（p﹤0.01）.Salinity stress had significant influence on the growth and the accumulation of lipid of P.tricornutum （p﹤0.01）. During the range of17‰⁷0‰of salinity, P. tricornutum could grow.Salt stress, either higher or lower than the normal salinity, could reduce the specific growthrate and the cell density. The maximal cell density of P. tricornutum under70‰salinitycondition was22.6%lower than that under the35‰salinity. The cell density under17‰salinity condition was9.6%lower than that under the35‰salinity. The highest biomass andthe highest lipid content were got from the35‰salinity. The maximal volumetricproductivity of lipid of the35‰salinity culture was much higher than that of other salinitycultures （p<0.01） and the volumetric productivity of lipids reached47.67mg·L^-1·d^-1, the arealproductivity of algal oil reached2.38g·m^-2·d^-1.The influence of nitrogen concentration on the growth of P. tricornutum was significant（p<0.05） with NaNO3as nitrogen source. The specific growth rate and biomasses increasedwith the increase of the nitrogen concentration in a certain concentration range. When thenitrogen concentration was4.72mmol/L, the parameters had a declined. Low nitrogen concentration can promote the accumulation of algae oil. The lipid content under low nitrogenconcentration was39.79%higher than that under the high nitrogen concentration. Theinfluence trend of biomass and lipid content under nitrogen concentration was opposite.Considering biomass and lipid content, it is concluded that the highest yield of lipid wasobtained from2.36mmol/L NaNO3concentration medium, reaching27.26mg·L^-1·d^-1and1.36g·m^-2·d^-1.In the range of temperatures set by the experiment, P. tricornutum grew normally duringthe range of10²2℃. The algal cells stopped growth and eventually died under27℃. Thespecific growth rate and biomass reached the maximum of P. tricornutum under16℃. Overthat then decreased. Low temperature was favorable to the accumulation of lipid in the cells.The lipid content of P. tricornutum under10℃was27.37%higher than that under22℃. Theproductivity of lipid under10℃was28.52%lower than that under16℃due tolower growthrate.Effects of different culture conditions on the biomass and lipid content of P. tricornutumwere studied. The contents of polysaccharides and proteins in algal cells under differentculture conditions were determined. Based on the influence of culture conditions on P.tricornutum cells metabolism, the culture conditions was optimized for lipid production. Theywere35‰salinity,16℃temperature,0.59mmol/L nitrogen concentration and5cm light path,with the highest lipid productivity of50.13mg·L^-1·d^-1and2.51g·m^-2·d^-1.