Improving The Yields Of Biomass And Desirable Metabolites Of Two Microalgae By Genetic Engineering

Increasing the growth rate and fatty acids content of Schizochytrium by genetic engineeringSchizochytrium sp., one of heterotrophic microalgae belongs to phylum Stramenopiles, Schizochytrium synthesizes rich unsaturated fatty acids. It has been found that timnodonic acid (DPA) and docosahexaenoic acid (DHA) account for more than60%of its total fatty acids and43%of its dry cellular weight. Schizochytrium is one of a few desirable heterotrophic microalgae which can be used to produce long chain unsaturated fatty acids through fermentation.During high density fermentation, transformation of glucose causes accumulation of acetic acid which will affect the fermentation negatively. In this research, the acetyl-coA synthetase gene, ACS, of E. coli was introduced into Schizochytrium sp. TIO1101with electroporation with such an introduction and the expression of the introduced gene verified by immunoblotting and polymerase chain reaction, In rotating bottle culture and high density fermentation, it was found that the acidity of transformant changed and the growth rate and glucose consumption rate of transformant were higher than those of the wild strain. As was evidenced by biomass and metabolite measurement, the biomass and the content of fatty acids were increase significantly in comparison with the wild. These findings indicated that over expression of ACS shifted the metabolism of Schizochytrium towards tricarboxylic acid cycle, and reduced the synthesis of acetic acid. Introduction of ACS gene has significantly improved the metabolism of Schizochytrium. Genetic transformation of Haematococcus pluvialisHaematococcus pluvialis is a single cell green alga. Newly formed cells of H. pluvialis appear to be spherical or oviform, and have two flagellates. H. pluvialis belons to genus Haematococcus, family Haematococcaceae, order Volvocales, class Chlorophyceae, phylum Chlorophata. Microalgae are the major source of astaxanthin, of them H. pluvialis contains the richest astaxanthin. H. pluvialis contains the richest astaxanthin among all known species accumulating this chemical, reaching4%of the dry cellular weight.Basing on the basis of Schizochytrium transformation and taking previous experience into account, Agrobacterium-medizted transformation and particle bombardment (gene gun) were tried in this study in order to express foreign gens stably in this alga. From available promoters, reporter genes, antibiotic resistance genes and target genes, a few recombinant plasmids were constructed. As were proved by fluorescence marker, antibiotic selection, and polymerase chain reaction, both Agrobacterium-mediated transformation and particle bombardment were effective for transferring foreign genes into H. pluvialis. Due to the biological characteristics of H. pluvialis and the complexity of planted experiment, the location and function verification of foreign protein need to be studied further. This will be a long term researching goal of the lab in which I tried to transform Haematococcus.