Song Wang

• A variety of bioactive substances have been extracted and identified from microalgae such as polyunsaturated fatty acids, polysaccharides, polypeptides, pigments as well as polyphenols. Although this topic is gaining increasing attention, mass production of microalgae-derived bioactive compounds is restricted by factors such as the low yield of algal biomass, the poor productivity of target compounds, immature extraction techniques, high capital and running costs, and insufficient knowledge in biosynthesis pathways. In this thesis, several critical obstacles in the large-scale production of bioactive compounds were addressed including the selection of appropriate algal species, the establishment of identification and purification methods, optimization of environmental conditions, and modification of photobioreactors. By a recently established high-resolution chromatography method, two fractions that showed antibacterial effects against Bacillus subtilis were eluted from Phaeodactylum tricornutum biomass, from which one was identified as pure polyunsaturated fatty acid – eicosapentaenoic acid, and the other designated as potential novel anti-bacterial compound(s) in Chapter 3. In Chapter 4, one benthic diatom, Cylindrotheca closterium, was selected from four tested species yielding the highest content of fucoxanthin and productivity. The optimal light condition, producing maximum fucoxanthin productivity and minimizing energy consumption, was predicted and validated. To better understand the metabolism of lipid accumulation in response to nitrogen starvation in diatoms and green algae, the lipidomes of the benthic marine diatom – C. closterium and the freshwater green alga – Scenedesmus sp. – were compared by an HPLC – coupled Micro-TOF mass spectrometric method in Chapter 5. In conclusions, the techniques developed in this thesis aimed to reveal the commercial feasibility of large-scale production of high-value bioactive substances and lipids from microalgae.