Electronic Thesis and Dissertation Repository


Master of Science




Dr. David Smith


The advent of photosynthesis facilitated the evolution of aerobic life on Earth. However, species such as Prototheca wickerhamii and Plasmodium falciparum, among many others, have lost photosynthesis and opted for a free-living/parasitic lifestyle. Despite this loss, these species have retained the plastid for its metabolic pathways, without which they would die. Polytomella is a nonphotosynthetic free-living alga, closely related to the photosynthetic model organism Chlamydomonas reinhardtii, and has been shown to lack a plastid genome. I set out to determine Polytomella plastid metabolic pathways using bioinformatics to look for mRNA and DNA homologous sequences matching pathway enzymes in model organisms. Interestingly, Polytomella possesses all enzymes required for amino acid, tetrapyrrole, starch, and carotenoid biosynthesis. However, it lacks enzymes that are plastid-encoded and/or are involved in chlorophyll biosynthesis. The progressive loss of carotenoid biosynthesis provides insight into photosynthetic loss, and Polytomella shows higher plastid functional complexity in comparison to parasitic species.