The Formation Of Phaeodactylum Tricornutum Cruciform Morphotype And Its Effects On Lipid Production Characteristics Of The Algae

Diatoms are important contributors to the carbon cycle, producing about20%ofthe organic carbon by photosynthesis. In recent decades, Phaeodactylum tricornutumhas been widely studied and reported as a model diatom and is generally recognizedas existing in three morphotypes: oval, fusiform and triradiate. The pleiomorphiccharacteristics of the microalgae were first described by Douglas P. Wilson in1946and the organism was capable of producing four morphotypes (oval, fusiform,triradiate and cruciform). Only the first three morphotypes are common, whilecruciform cells are rare and regarded as irregular. Since1946, cruciform cells haverarely been reported. Subsequent studies on Phaeodactylum tricornutum have mainlyconcerned strains with one to three of the common morphotypes. As the onlyrepresentative of the suborder Phaeodactylineae, family Phaeodactylacea, genusPhaeodactylum, new insights into the polymorphism of Phaeodactylum tricornutum,especially the description of the forth morphotype, have important ecologicalsignificance. In this study, we successfully cultured the fourth morphotype ofPhaeodactylum tricornutum–the cruciform morphotype in a high proportion which isreported for the first time. We also demonstrated the transformation from cruciform toother common morphotypes and clarified the fatty acid characteristics of this uniquestrain at different temperatures. The main findings are as follows:A rare Phaeodactylum tricornutum cruciform morphotype was obtained andstabilized with a proportion of more than31.3%in L1medium and is reported for thefirst time. Long-term culture and observation showed that the cruciform morphotypewas capable of transforming to the oval form following the degeneration of arms bytwo processes. After three months of culture, four morphotypes existed in a relativelystable proportion in culture for six months (10.5%for oval,11.3%for fusiform, 37.2%for triradiate and41.0%for cruciform).Low temperature was particularly beneficial for cruciform cell formation. As theculture temperature decreased from25oC to10oC, the percentage of the cruciformmorphotype increased from39.1%to55.3%approximately. The abundant cruciformcells endowed this strain with unique fatty acid characteristics. The strain cultured at15oC showed both maximum content of neutral lipid in a single cell and total yield.The maximum content of fatty acid methyl esters was C16:1for Phaeodactylumtricornutum cultured at four temperatures (43.82%to50.82%), followed by C16:0(20.47%to22.65%).Fourier Transform Spectroscopy was employed for determination ofbiomacromolecular contents (mainly refers to carbonhydrates, lipids and proteins) inPhaeodactylum tricornutum of different stage cultured under15oC,20oC and25oC.The results showed that different tendencies appeared at different temperatures. Thetrend of biomacromolecular contents at15oC and25oC were samilar, whichaccumulated with the extension of incubation time in platform stage. While at20oC,carbonhydrates and proteins contents grew to the peak at early stage of platform,which was different from tendency of lipids. And the content of lipids at20oCmaximized at metaphase of platform, lagging behind carbonhydrates and proteins.Fourier Transform Spectroscopy method can detect relative contents of mutiplebiomacromolecular of Phaeodactylum tricornutum using a little sample, whichprovides a new way for further research on metabolic mechanism. Unique fatty acidcomposition endowed this strain with excellent quality for biodiesel production.Combined with outdoor temperature variation characteristics in different seasonsin Qingdao,9microalgae including Phaeodactylum tricornutum CCMM2004wereevaluated to assess their potential for biodiesel production using emissions of powerplants outdoors by entropy weight theory. Five indicators including the oil yield, oilcomposition, CO2tolerance, broken difficulty and temperature adaptability wereselected to calculate entropy weight based on laboratory measured data. Weights forthe above five indicators in spring and winter were0.261,0.002,0.059,0.211and0.467respectively, while in summer and autumn were0.098,0.001,0.022,0.079and 0.801respectively. Based on the above results, microalgae with maximum potentialfor large-scale biodiesel production in spring and winter was Phaeodactylumtricornutum CCMM2004, while in the summer and autumn was Isochrysis galbanaC5001. This method provides an effective way for microalgae strains selected foroutdoor large-scale biodiesel production.