Genetic and phylogenetic characterization of microalgae strains in view of their exploitation for CO2 capture and biofuel production

In the light of for sustainable development, microalgal biodiesel, as a renewable and sustainable energy type, has enjoyed a surge in popularity. In fact, differently from the first generation biofuels, the use of microalgae to produce bioenergy does not involve the triggering of "food for fuel" competitivity and thus represents a sustainable mean to face significant concerns, such as wars and political instabilities deriving from oil reserves shortage. Morevoer, the high oil yields and less land use are the main advantages of microalgae. However, in order to make the current technology viable at the large-scale, several limitations should be overcome. In particular, biomass and lipid productivities should be further increased and all the downstream processes, from harvesting to lipid extraction, should be optimized. To these aims, high efforts involving high investments should be done in order to implement an intensive multidisciplinary research activity both at the laboratory and the industrial scale. The microalgae cultivation is the base of biofuel development and suitable genetic engineering strategies have to be developed in order to augment the microalgae oil content and their growth rate so that biofuels production could performed in a sustainable way. In particular, the creation of new microalgal strains intrinsically characterized by high lipid productivities as well as by a good tolerance to high CO2 levels is an ambitious goal which might be achieved only once their genome is known. The results presented in this thesis represent the first step needed to design a genetic approache which may eventually facilitate large-scale production of algae. The use of transgenic microalgae for the production of bioproducts represent an enormous economic and biotechnology promise, because algal production combines the simplicity and speed of haploid, single-cell genetics in an organism with elaborate biosynthetic potential, and with the associated economic benefit of using photosynthesis to drive product formation. As technology continues to be progressed and algae production industrialization continues to be improved, microalgae energy as the third generation biofuel will contribute their own strength to relieve the tense situation of resources. The contribution of the present work, to this general target can be briefly summarized as follows. The growth kinetics of C. sorokiniana has been investigated along with their corresponding lipid content, both batch and helical photobioreactors. The main results achieved during this activity are the knowledge of the effect of nitrogen concentration in solution on the growth rate and lipid content of C. sorokiniana. These informations represent the first step towards the development of a nitrogen based strategy for the optimization of lipid productivity of C. sorokiniana cultures. As far as the genetic characterization activity, the chloroplast and mitochondrial DNAs of two strains, i.e. C. sorokiniana and C. variabilis, respectively, have been sequenced for the first time in the literature. The obtained results allowed to perform a phylogenetic assessment involving different microalgae strains belonging to the Chlorella clade. Such results represent the first important step towards the development of genetic engineering strategies aimed to improve the current microalgae based systems for the production of biofuels and the capture of CO2.