Systems Analysis of Metabolism and Physiology of the Oil-Producing Green Alga Botryococcus braunii Race B (Showa)

The colony-forming green microalga Botryococcus braunii is mostly known for its ability to produce an abundance of liquid hydrocarbons. However, geochemical studies have found fossilized remains of the species in petroleum source rocks from around the planet, dating as far back as the Precambrian eon. Thus B. braunii is considered a source of petroleum throughout the geological ages and presents an interesting model to study hydrocarbon metabolism. To better understand the biochemical and genetic systems that underpin the unique properties of B. braunii, we have sequenced and analyzed its genome. Using a comparative genomics approach, we identified 187 functions that are unique in B. braunii among the Viridiplantae (green algae and land plants), and 402 functions that are unique in B. braunii among the green algae. Thus B. braunii shares 215 functions with land plants that other green algae do not. These functions include parts of the photosynthetic apparatus, the ubiquitin system, cytochrome P450s, peptidases, cytoskeleton proteins, and others. To further understand the active interpretation of genomic information, we sequenced the transcriptome of B. braunii every six hours over the course of three days. The goal of this experiment was to determine the gene expression patterns associated with light/dark transitions. Interestingly, we found several strong coexpression modules that cycle, not according to light or dark conditions, but by time of day, indicating the presence of circadian regulatory mechanisms. To determine the impact of gene expression and time of day on metabolism, we generated metabolomics data for each of the biological samples that were utilized to obtain the transcriptome data. Targeted and untargeted analyses of polar and nonpolar metabolites revealed that unlike transcription, metabolite pools do not appear to significantly change with time of day. The information presented in this dissertation adds great value to our fundamental understanding of the systems governing B. braunii metabolism and physiology. With this knowledge, we could design genetic systems in heterologous hosts to mimic the properties of B. braunii pathways. This could result in synthetic pathways for hydrocarbon production with strong metabolic flux, technology that is vital for the development of sustainable bioproducts