Research On The Collection And Lipid Synthesis Pathway Of Oil-producing Microalgae

Global industrialization makes the consumption of fossil fuels accelerate, buthuman’s energy demands are sharply growing. Meanwhile, burning of fossil fuels hascaused environmental degradation and climatic anomaly. Hence, people begin to payclose attention to the development and utilization of renewable energy which isenvironmentally friendly. Based on above reasons, scientists from many countrieshave made many researches to soybean, corn, palm, and other higher plants, trying tofind the right material to produce the biological fuels which can meet demands of thehuman in quantity and quality. Although many achievements have been obtained andsome problems about energy demands have been solved, there are still a series ofbarriers that hinder the process, such as shortage of raw materials and occupyingplough lands. In this context, the microalgae have become the favour of researchersdue to their high lipid contents, the short growth cycles, mass cultivation and the highphotosynthetic efficiency.There are still several problems to be solved for the production of biodiesel withthe microalgae, although there has been many advantages. For example, themicroalgae are usually rich in lipids, but the proportion of12:0and14:0that are themost suitable for the production of biodiesel is not high. Other studies show that theratio of total lipids to dry weight will rise under special environment, but the biomasswill also drop sharply, leading to the final yield of total lipids is not high. In view ofthe above problems, researchers should find solutions from at least two aspects.Firstly, try to separate some new algae strains from the wild waters which are withhigh lipid contents, large biomass, fast growth speed and excellent tolerability ofenvironment. Due to the development of navigation technology, the sea samplingbecomes more convenient and sampling range becomes much vaster. These all speedup the pace of sampling new algae from natural sea areas. Secondly, breed microalgaeby means of genetic engineering in order to resolve the contradiction of the lipid contents and dry biomass. The genetic information is enriched and the applicationtechnologies (excessive expression, gene silencing, gene knock out, RNA interferenceand so on) are ripe. These also greatly support the development of buildingmicroalgae strain through genetic engineering. In addition, many scientists madeefforts to genetically modify higher plants or microorganism by genetic engineeringmeans, providing valuable information for its application in microalgae.Phaeodactylum tricornutum belongs to order Naviculales which is one of classBacillariophyceae. Because of its high lipid content, fast growth rate, and abundantEPA (eicosapentaenoic acid,20:5n3), it has attracted the researchers’ attention. Inaddition, the whole genome sequencing has been accomplished and many kinds ofgenetically modified systems also have been established. All these makePhaeodactylum tricornutum the pop microalgae in the field of microalgae biodiesel.Ithas been studied that the lipid content of Phaeodactylum tricornutum will greatlyincrease with nitrogen deficiency, but the mechanism has been not reported.Based on these, in this study, more than70culturable microalgae strains havebeen isolated after sampling from the Yellow sea and Bohai sea. With the Neighbour-Joining trees of the18S rRNA genes and the rbcL genes sequences and theirmorphological information, the70strains were been identified, laying the foundationof the search of oil-producing microalgae. Selection of the target genes is rathersightless while breeding microalgae by means of genetic engineering. Phaeodactylumtricornutum was chosen for this study. The transcription levels of11key enzymesgenes related to the lipid synthetic pathway were assayed with Real-time PCR and thelipid contents were determined with Nile red when Phaeodactylum tricornutum wastreated with nitrogen deficiency. Analyzing the correlation, several genes play positiverole in the lipid synthesis. These provide valuable information for gene expression inPhaeodactylum tricornutum. Meanwhile, the lipid synthetic pathway ofPhaeodactylum tricornutum was also inferred in this study.