Optimizing yields of bioproducts in mixotrophic cultures of micro algae

浮游植物是单细胞海洋和淡水植物，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(基本营养素，如omega-6脂肪酸，但也包括三酰甘油酯，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类)，以及潜在的药物。大规模养殖浮游植物也被测试为一种处理高营养废水的方法，以修复流域和沿海水域的富营养化。沿海富营养化是造成全球范围内缺氧和有害藻类水华增加的原因。许多产生高价值化合物的浮游植物可以混合营养生长，这是一种细胞既是自养的(光合作用的)又是异养的(利用不稳定的有机化合物)的混合营养模式。混合营养可以极大地提高细胞产量，但人们对此知之甚少。因此，对最佳条件的筛选是通过反复试验进行的。该项目将通过扩展一个广泛使用的模型--动态平衡模型，开发一个概念框架来预测混合营养生长和细胞组成随光强、温度和养分可获得性的变化。这将定义用于扩展模型的物种的最佳生长状态，使三种高价值化合物的产量最大化。它还将提供一种手段，在未来重点优化产生其他有价值化合物的菌株的条件。混合营养培养的细菌污染或多或少是不可避免的，细菌可以竞争浮游植物对有机底物的竞争，并可能导致大规模死亡。因此，在不抑制浮游植物生长的情况下抑制细菌生长是经济上可行的养殖所必需的。该项目将测试一项经过验证的技术--紫外线-C辐射--作为一种差异化应激源的使用，这种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，许多有价值的产品在压力条件下会被上调。当培养达到最佳收获条件时，评估栽培是否成功。生物光学技术是这方面的理想选择，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。该项目将开发和研磨真实的生物光学特征，以评估生产高价值化合物的细胞收获的准备情况。提高产量和更有效地筛选菌株将促进下一代浮游植物的培养，将其作为目标天然产品的细胞工厂，并作为修复受污染废水的手段。这将转化为一种新的水产养殖形式，并使加拿大和世界各地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.