Optimizing yields of bioproducts in mixotrophic cultures of micro algae

浮游植物是单细胞的海洋和淡水植物，可以作为有价值的天然产品的来源进行培育。这些包括脂类（必需营养素，如omega-6脂肪酸，也包括三酰基内酯，生物柴油的前体），可用于原料的蛋白质，抗氧化剂（类胡萝卜素和类黄酮），以及潜在的药物。大规模培养浮游植物也已被试验作为一种处理高营养物废水的手段，以补救流域和沿海水域的富营养化。沿海富营养化是造成缺氧和世界范围内有害藻华发生率增加的原因。这两种方法在环境和经济上都很昂贵。许多产生高价值化合物的浮游植物可以混合营养生长，这是一种混合营养模式，其中细胞既自养（光合作用）又异养（利用不稳定的有机化合物）。混合营养可以大大提高细胞产量的生长速度，但对其了解甚少。因此，筛选的最佳条件进行试验和错误。该项目将开发一个概念框架，通过扩展一个广泛使用的模型，即动态平衡模型，来预测混合营养生长和细胞组成作为光强、温度和养分可用性的函数。这将定义用于扩展模型的物种的生长最优，最大化三种高价值化合物的产量。这也为今后重点优化菌株生产其他有价值化合物的条件提供了一种手段。混合营养培养的细菌污染或多或少是不可避免的，细菌可以与浮游植物竞争有机基质，并可能导致大量死亡。因此，在不抑制浮游植物生长的情况下抑制细菌生长对经济上可行的养殖至关重要。该项目将测试使用一种经过验证的技术，即紫外线- c辐射，作为一种不同的应激源，可以在不影响浮游植物的情况下抑制细菌生长。最后，许多有价值的产物在应激条件下被上调。栽培达到最佳收获条件时的成功栽培评价。生物光学技术是理想的，因为它们对细胞组成和功能的变化很敏感，是非破坏性的，并且可以实时使用。该项目将开发和建立真实的生物光学特征，以评估生产高价值化合物的细胞的收获准备情况。菌株的提高产量和更有效的筛选将促进下一代浮游植物的培养，使其成为目标天然产物的细胞工厂和修复污染废水的手段。这将转化为一种新的水产养殖形式，并使加拿大和全世界的沿海和内陆水域更加清澈。

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.