UC San Diego

The search for new sources of sustainable and renewable energy is one of the most important issues of our time. Broadening our energy base not only thwarts the issues of dependence on foreign oil and national energy security, but also creates a more stable and sustainable energy sector. Biomass is one such source of renewable energy that has been recently developed over the last few decades, and microalgae were identified half a century ago as potential producers of fuel-relevant molecules. Members of this group can produce a variety of molecules including lipids that can be converted into liquid fuel molecules, carbohydrates that can be fermented into ethanol, and biohydrogen. This dissertation work focuses in particular on the pathways associated with lipid production in microalgae. This work shows that it is possible to increase lipid accumulation in microalgae through metabolic engineering without affecting growth. The pathway manipulated here is lipid catabolism, or the breakdown of lipids. This work used transcriptomics to guide the identification of a target lipase in the lipid catabolism pathway. Knock-down of this enzyme in the diatom Thalassiosira pseudonana generated strains that grew comparably to wild-type but exhibited increased TAG accumulation during exponential growth, stationary phase and nutrient starvation-induced lipid accumulation. This dissertation also describes a novel approach for using native sequences to conduct metabolic engineering. By using the knock-down phenotypes of increased TAG accumulation and increased membrane intactness, we were able to generate and select knock-down strains using only native sequences of T. pseudonana, thus exempting these strains from the classification of "genetically modified organism" in the U.S. Finally, this dissertation looks beyond the science of algal biofuels to investigate and analyze the policy landscape for cultivating algal biomass. The large-scale cultivation of algae is in essence agriculture, and it is imperative that federal agricultural programs are expanded to cover and support algae as equal commodities. Overall this dissertation expands our knowledge of lipid metabolism in microalgae, provides methods for increasing lipid yields in production systems, and explores the support that is available and needed to transform research and development efforts into a commercially relevant industry