Graduate Thesis Or Dissertation
 

Two-stage photobioreactor cultivation for enhancing lipid production from diatom cells by controlled silicon limitation

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/12579v10m

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  • There is significant interest in utilizing microalgae as a source for biofuels. Diatoms are a class of single-celled microalgae which make silica cell walls and require dissolved silicon as a substrate for cell division. Manipulation of soluble silicon delivery to the culture offers a route to control cell cycle and lipid production. A two-stage, semi-continuous photobioreactor cultivation process was developed to induce the production of lipid-rich algal biomass from the centric diatom Cyclotella sp. In Stage I of the process, algal cells were grown up to high density until all of the dissolved silicon in the feed medium was consumed. The cells were in the silicon-starved state when the cell density was constant for 24 hours and the dissolved silicon concentration was near-zero and ceased to change. In Stage II, fresh medium containing dissolved silicon was perfused into the reactor for a 48, 72 or 96 hours. The silicon was rapidly consumed by the silicon-starved cells under a surge uptake mechanism, maintaining the same near-zero silicon concentrations that were present at the end of the first stage, so that silicon starvation was maintained within the system. Cells grown with 48 and 72 hour perfusion yielded high lipid concentrations (>45% of dry cell weight) and high productivity in the algal biomass while maintaining biomass generation. The lipid composition was analyzed by GC/MS and seven fatty acids were identified including the three main fatty acids: palmitoleic acid, palmitic acid and eicosapentanoic acid. It was determined by GC analysis that the lipid composition remains constant once silicon starvation is achieved, regardless of perfusion addition of additional silicon. This study illustrates that a bioreactor cultivation strategy enhances lipid production by algal cultures for the purpose of algal biodiesel production.
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