胞外聚合物（EPS）对微藻砷富集和代谢影响机制的研究

Extracellular polymeric substances (EPS) from microalgae are one type of important substances in the "water-algae" interface and have good application prospects in the field of arsenic (As) wastewater treatment. It has been shown that EPS are related to As accumulation and transformation in microalgal cells, however, mechanisms of such relationships have not been elucidated and more research is urgently needed. In our previous research, we found that microalgae with higher EPS content on the cell surface had more As adsorption and transformation than other algae. Therefore, we hypothesize that "EPS affects the processes of As accumulation and metabolism through modifying the surface characteristics of microalgal cells". In order to varify the above hypothesis, this project will grow different microalgae, set up various growth stages, nutrient conditions, solution pH, and symbiotic bacteria to study the changes of structure, main components and functional groups of microalgal EPS. Removal of EPS and As treatment will be conducted to determine the impacts of microalgal surface properties, amounts of binding sites and types of functional groups on the As distribution, speciation and transformation in microalgae with a number of analytical techniques. These data will reveal the relationships between microalgal EPS and As accumulation and metabolism, as well as their influential factors and underlying mechanisms. The results of this project may be of great significance in further clarifying the role of microalgae in As biogeochemical cycle, and developing novel technologies in the environmental As pollution remediation.

微藻胞外聚合物（EPS）是“水—藻”界面一类重要的物质，在含砷废水的生物处理领域中具有良好的应用前景，然而EPS对砷富集和代谢影响的具体机制还不清楚，亟待深入研究。申请人课题组前期的研究结果表明，EPS较多的微藻对砷的吸附和价态转化的数量明显高于其它微藻，因而提出“EPS改变微藻细胞表面性质，进而影响砷的富集和代谢过程”的假设。为验证这一假设，本项目将选择不同类型微藻，优化EPS的提取方法，设置生长阶段、营养盐含量、溶液pH、共生细菌等条件，研究微藻EPS形貌、主要成分和官能团的变化规律，在此基础上探索有无EPS条件下，微藻细胞表面性质、结合位点数量、官能团种类等因素的变化，以及这些变化对微藻砷的吸附、吸收和形态转化的影响，以期阐明EPS与微藻砷富集和代谢的关系及其影响因素和机理。研究结果对于进一步明确微藻在砷的生物地球化学循环中的作用、研发环境砷污染修复新技术都具有十分重要的意义。

EPS 是微生物细胞分泌的有机大分子物质，包括多糖、蛋白质、核酸、脂质和腐殖质等多种组分，能进一步增加微藻细胞的比表面积和阴阳离子吸附能力，去除多种污染物如氮磷、重金属、有机污染物、纳米颗粒等，并促进其形态转化，以减少对细胞的毒害，因此在含砷等重金属废水的生物处理领域中具有良好的应用前景。然而，以下几个科学问题还没有明确的答案：1）砷如何影响微藻EPS的数量和组成？2）EPS如何影响微藻对砷的富集和形态转化？3）微藻EPS是否具有水体砷污染修复的潜力？为回答这些问题，揭示EPS对微藻砷吸附、吸收和代谢影响的具体机制，本项目选取三种典型微藻，即集胞藻（蓝藻）、莱茵衣藻（绿藻）、三角褐指藻（硅藻），在以下3个层面开展研究：1）微藻EPS的提取和表征；2）砷处理下微藻EPS的数量和组成的变化；3）EPS对微藻砷富集和形态转化的影响。结果表明：综合EPS提取量、细胞完整性和提取成本等因素，三种微藻EPS的最佳提取条件分别为：集胞藻--加热法（50℃，20 min）、莱茵衣藻--加热法（50℃，3 h）、三角褐指藻--EDTA提取法（20 mmol·L-1 , 3 h）。EPS中含有C-O-C、C=O、-NH和-OH等多种官能团，且都能与砷结合。上述微藻在砷酸盐和亚砷酸盐的处理下，EPS的分泌量均有所上升，其中集胞藻和三角褐指藻的多糖响应大于蛋白，莱茵衣藻的蛋白响应大于多糖，多种官能团的数量发生变化，说明砷可诱导微藻分泌EPS，藻细胞通过改变EPS的数量和组成和数量应对砷胁迫。对提取EPS和对照条件下的藻细胞进行比较，发现EPS显著促进了三种微藻对砷的富集，增加了砷的胞外吸附、减少了砷的胞内吸收，促进了氧化还原、甲基化等形态转化，表明EPS显著影响了微藻对砷的富集和代谢。EPS有多种结合位点与砷进行络合，减少进入胞内的砷，缓解了砷对微藻细胞的毒性。这些结果证明了微藻EPS具有水体重金属污染修复的应用潜力。