The Compatible Solute Glycerol as a Photosynthetic Sink and Energy Carrier in Freshwater and Marine Chlamydomonas

The purpose of this thesis was to explore fundamental relationships between the photosynthetic production of energy carriers, the ceiling of photosynthetic capacity, and the regulation of photosynthesis in algae and how this insight may (i) serve to enhance the principal understanding of the limits of primary productivity and (ii) open up novel applications in the context of the generation of biomaterials and bioenergy from renewable resources. Methods were developed or refined to separate algae from their culture medium to study accumulation and release of glycerol from freshwater and marine species of the green algal genus Chlamydomonas under various culture conditions (primarily different salinity and light levels). Culture density, chlorophyll content, growth rate, photosynthetic oxygen evolution, respiration, and intracellular and released glycerol were measured. The freshwater species C. reinhardtii released considerably more glycerol to the external environment in response to increasing levels of salinity compared to the marine species C. euryale, suggesting that limitations to the ability to internally accumulate and retain glycerol as an osmoregulatory compound may be involved in the inability of the freshwater species to grow at elevated salinities. While the freshwater species exhibited no downregulation of photosynthesis between 0 and 0.2 M NaCl, the marine species exhibited significant upregulation of photosynthetic oxygen evolution between 0.2 and 2.0 M NaCl in the medium, indicating that internal glycerol accumulation, unlike sugar accumulation, does not interact with sugar-signaling networks that induce photosynthetic downregulation upon internal photosynthate accumulation. At elevated salinities, the freshwater species nearly ceased growing yet exhibited no downregulation of photosynthesis, suggesting glycerol may act as a sink for photosynthetic energy. These findings suggest that stimulation of glycerol synthesis and release by Chlamydomonas via environmental manipulation is an attractive option for algal energy-carrier production, which could in turn be used as a feedstock for bioenergy and biomaterial production from renewable resources