Lipid metabolism and storage in the microalga Chlamydomonas reinhardtii

Abstract

Neutral lipid accumulation by microalgae has recently regained considerable interest as these organisms are considered as a promising feedstock for the production of renewable biodiesel. Nitrogen deprivation is well described as a trigger for neutral lipid accumulation in various species of microalgae including Chlamydomonas.However nitrogen deprivation provokes a stop in protein synthesis and cell division, therefore limiting microalgal biomass productivity. In order to elucidate mechanisms of lipid accumulation in Chlamydomonas reinhardtii, a mutant exhibiting elevated TAG levels is characterized. The mutant exhibits reduced chlorophyll but elevated starch and neutral lipids under strong illumination in replete medium. Genetic characterization has revealed 41 missing genes whose detailed study is beyond the scope of this thesis. However this mutant has highlighted the link between luminosity and TAG biosynthesis. High light has also previously been reported as a trigger to induce oil accumulation. To gain insights into the differences in molecular mechanisms behind oil accumulation processes under nitrogen starvation to that of high light, lipidomic changes in separate cultures subjected to the either stress condition was performed. Results showed that despite intracellular TAGs were found to accumulate to lower levels in response to high light in comparison to nitrogen deprivation; the TAGs productivity was higher due to a persistent biomass production. Furthermore differences in both the lipid and protein composition were observed in lipidomes and proteomes determined by pure extracts of lipid bodies isolated from both conditions revealing differences in lipid bodies isolated from different conditions