共培养诱导微藻细胞自絮凝沉降的研究

High costs is the great obstacle to produce biodiesel from microalgae biomass. Cost saving is important for microalgae oil production. The cost of microalgae biomass harvesting is much greater than its culture. This process is complex, and characterized with high investment and high energy consumption, that seeking for a convenient, effective and low-cost method to harvest microalgae biomass is put on the agenda urgently. The sedimentation from flocculants of microalgae cells can improve the efficiency of separation, simplify the operation steps and cut the costs effectively. The co-cultivation technique has been widely applied in purification treatment of sewage, but research need to be put forward further for autoflocculating sedimentation of microalgae cells. In our previous experiments, we find that the co-cultivation in microalgae can enhance the productivity of microalgal oil and improve the oil quality, and may seem easy to change synthesis of Extracellular Polymeric Substances (EPS) components to induce autoflocculation of microalgae cells. In this study, we will systematic research the law of occurrence and change of the EPS components, and their effect on surface characteristics of microalgae cells by altering the co-cultivation condition, and combining proteomics techniques to expound mechanism of co-cultivation to induce autoflocculating sedimentation of microalgae cells. Clear mechanism would be beneficial to regulate autoflocculation, and provide theoretical basis for reducing the production cost of microalgal oil.

微藻生物质制备生物柴油的最大障碍是生产成本过高，降低微藻油脂的生产成本是关键。微藻生物质采收所需的费用远大于微藻养殖的费用，采收过程复杂、高能耗及高成本，找寻一种简便、效率高、成本低的微藻生物质采收方法是目前急需要解决的问题。微藻细胞絮凝引发的沉降能够提升分离效率，减化操作步骤，有效降低采收成本。共培养技术已广泛应用于污水净化处理方面，但在自絮凝沉降方面的研究有待进一步深入。申请者在前期研究中发现，藻-藻共培养可以提高油脂产率和改善油脂品质，同时还可能改变胞外聚合物各组分的产生，具有诱导微藻细胞自絮凝沉降的可能。本课题拟通过改变藻-藻共培养条件，对胞外聚合物各组分的产生、变化规律及其对微藻细胞表面特性的影响进行系统研究，结合蛋白质组学的研究方法，阐述共培养诱发藻细胞自絮凝沉降的机理，为调控微藻自絮凝降低微藻油脂生产成本提供理论依据。

随着全球经济持续发展，能源危机和环境问题快速加剧，石化燃料等不可再生资源面临日渐枯竭的严峻现状。微藻油脂为原料制备的生物柴油是石化燃料的理想替代品，但是微藻的生物质采收成本过高，限制其商业化发展。利用微藻自絮凝对微藻生物质进行采收，具有低能耗、高效率的优势，具有较好的应用潜力。共培养技术，具有诱发藻细胞自絮凝沉降的可能，并有望获得高油脂产率和良好的脂肪酸组成。在本研究中，以微藻Desmodesmus sp. ZFY和Monoraphidium sp. QLY-1为研究对象进行共培养。7天后，共培养体系的油脂产率达到最大值，为99.75mg L d-1，且微藻的脂肪酸组成符合生物柴油的基本要求。在自然沉降4h后，共培养体系的微藻絮凝沉降率高达85.33%，显著高于微藻Desmodesmus sp. ZFY（57.98%）和微藻Monoraphidium sp. QLY-1（32.45%）单独培养下的自絮凝沉降率。Zeta电位不是造成共培养体系中微藻自絮凝效率提高的主要因素。共培养条件下产生的松散结合型胞外聚合物（LB-EPS）在微藻的自絮凝过程中发挥了重要的作用，LB-EPS中多糖的含量和组成与藻细胞的聚集密切相关。相比于微藻Desmodesmus sp. ZFY（27.01%）和微藻Monoraphidium sp. QLY-1（27.35%）单独培养下的多糖含量，共养体系中LB-EPS的多糖含量得以提高（46.53%）。共养体系LB-EPS多糖主要是甘露糖、葡萄糖、岩藻糖、葡萄糖醛酸和半乳糖组成，比例为4.41:3.41:1.22:1.07:1，甘露糖、和葡萄糖含量高于单独培养，也许是自絮凝沉降率增加的重要因素。通过单独培养和共培养微藻的转录组学和蛋白组学联合分析，关联上的差异表达基因和差异表达蛋白中有同步上调表达的198个蛋白，有27个蛋白关联到参与调控EPS中多糖合成途径的10个关键酶，说明了LB-EPS中多糖的含量增加与组成变化的原因。研究构建“共培养-胞外聚合物-细胞自絮凝”的内在联系，揭示了共培养可能会导致环境压力的增强，微藻在胁迫环境下做出应激反应，促进了EPS的大量合成；EPS中的LB-EPS多糖含量增加以及多糖组成发生变化，可能会使微藻细胞自絮凝沉降更容易发生。本项目为调控微藻培养过程，高效采收微藻生物质，降低微藻油脂生产成本提供了一种有效的方法。