Optimizing yields of bioproducts in mixotrophic cultures of micro algae

Phytoplankton are single-celled marine and freshwater plants that can be cultivated as sources of valuable natural products. These include lipids (essential nutrients like omega-6 fatty acids but also triacylgylerides, the precursors of biodiesel), proteins that can be used in feedstocks, antioxidants (carotenoids and flavonoids), and potential pharmaceuticals. Mass culture of phytoplankton has also been tested as a means of treating wastewaters that are high in nutrients to remediate eutrophication in watersheds and coastal waters. Coastal eutrophication is responsible for hypoxia and an increased incidence of harmful algal blooms worldwide. Both are environmentally and economically costly.Many phytoplankton that produce high-value compounds can be grown mixotrophically, a mixed nutritional mode in which the cells are both autotrophic (photosynthetic) and heterotrophic (utilizing labile organic compounds). Mixotrophy can greatly increase growth rates are cell yields but is poorly understood. Consequently, screening for optimal conditions proceeds by trial and error. This project will develop a conceptual framework for predicting mixotrophic growth and cell composition as a function of light intensity, temperature, and nutrient availability by extending a widely-used model, the Dynamic Balance model. This would define growth optima for the species used to extend the model, maximizing yield of three high-value compounds. It would also provide a means to focus optimization of conditions for strains producing other valuable compounds in the future. Bacterial contamination of mixotrophic culture is more-or-less inevitable and the bacteria can out-compete the phytoplankton for the organic substrates and can cause mass mortality. Suppression of bacterial growth without inhibiting growth of the phytoplankton is therefore essential for economically-feasible cultivation. This project will test use of a proven technology, ultraviolet-C radiation, as a differential stressor that could inhibit bacterial growth without affecting the phytoplankton. Last, many valuable products are up-regulated under conditions of stress. Successful cultivation assessing when the culture has reached the optimum condition for harvesting. Bio-optical techniques are ideal for this as they are sensitive to changes in cell composition and function, are non-destructive, and can be used in real time. This project will develop and ground-truth bio-optical signatures that would assess readiness for harvest of cells producing high-value compounds. The enhanced production and more efficient screening of strains will facilitate next-generation cultivation of phytoplankton as cell factories for targeted natural products and as means of remediating contaminated wastewaters. This would translate to a novel form of aquaculture and to clearer coastal and inland waters in Canada and worldwide.