典型水华蓝藻砷代谢对不同形态磷源的响应与机制

Arsenic (As) is not only a major hazard metalloid but a natural environmental contaminant to which humans are routinely exposed in food, water, air, and soil. The risks of As in water environment were widely acknowledged. Water contamination with As and algal blooms are universal and urgent problems that requires immediate actions. Although As can be found in the environment in several oxidation states, the pentavalent arsenate (AsⅤ) is generally the more stable and predominant form in natural water, which can be accumulated and converted into other species by phytoplankton. Currently, researches on the risks of AsⅤ and cyanobacterial blooms are one of the critical topics about the health and safety of aquatic enviornment. Scince phytoplankton are at the base of the food chain in aquatic ecosystems, they play an important role in As biogeochemical cycles. Phosphorus is regarded as the main culprit of eutrophication in lake systems where levels positively affect the growth rate of phytoplankton. Owing to the similar biochemical characteristics of As and phosphorus, the metabolism of AsⅤ by phytoplankton could be influenced and regulated by the ambient phosphorus concentration. Both organic phosphorus and orthophosphate can be assimilated and utilized as phosphorus sources by some dominant cyanobacterial bloom species such as Microcystis aerugiosa, Aphanizomenon flosaquae. The potential effect of organic phosphorus compounds on the metabolism of AsⅤ by phytoplankton might be different from orthophosphate. However, the comparative researches on different forms of phosphorus influencing the AsⅤ metabolism have been still ignored. Little information, so far, is available regarding the effects of various phosphorus forms on the AsⅤ metabolism by phytoplankton in water environment. Cyanobacteria as one of the largest and most important groups of prokaryotic autotrophs are generally selected as the model organisms for studying various biological processes in water environment. Therefore, this proposal would investigate systematically in the changes of As total amount and species, algal growth stress by the integration of phosphorus and As, phosphorus uptakes and forms, some relative metabolic enzymatic activities of phosphrus and As, subcellular distribution of arsenic in algae cells and primary phosphorus transporters PstB gene expressions during AsⅤ metabolism by two representative cyanobacteria (Microcystis aeruginosa and Aphanizomenon flosaquae) under different forms of phosphorus sources. In turn, the main objectives of this proposal are to identify the influences of different forms of phosphorus sources on the AsⅤ metabolism of cyanobacteria in aquatic environment, and to reveal their potential mechanisms. The results of this proposal would benefit our understanding of phosphorus effects on As transport and transformation in water enviroment, and provide insights into the As geochemical cycles in aquatic environment.

砷作为一种全球性污染的重要有毒物质，在水环境中的风险受到广泛关注。水环境中浮游藻类对砷的代谢具有重要作用，是砷地球化学循环研究的重要组成部分。磷与砷相似的化学结构使得浮游藻类砷代谢受环境中磷的调节和影响。有机、无机不同形态磷源对浮游藻类砷代谢具有潜在的差异性影响。迄今为止有关浮游藻类砷代谢对不同形态磷源响应的研究极近空白，缺乏不同形态磷源对砷地球化学循环的比较研究。本项目以典型水华蓝藻和砷酸盐为研究对象，对不同形态磷源影响水华蓝藻砷代谢的总量与形态差异、水华蓝藻受磷与砷二者影响时的生长胁迫、磷含量与形态、砷与磷代谢酶活性、砷的亚细胞分布、磷关键转运蛋白PstB表达等进行全面、系统地研究，探明不同形态磷源对水华蓝藻砷代谢的影响，揭示水华蓝藻砷代谢对不同形态磷源的响应机制。研究结果可促进磷对砷迁移转化作用的理解，提升对水环境中砷地球化学循环的理论认识，促进水环境砷污染潜在风险的管理水平。

砷作为一种全球性污染的重要有毒物质，在水环境中的风险受到广泛关注。磷与砷相似的化学结构使得浮游藻类砷代谢受环境中磷的调节和影响。有机、无机（DIP）不同形态磷源对浮游藻类砷代谢具有潜在的差异性影响。迄今为止有关浮游藻类砷代谢对不同形态磷源响应的研究极近空白，缺乏不同形态磷源对砷地球化学循环的比较研究。本项目以典型水华蓝藻和砷酸盐为研究对象，对不同形态磷源(腺苷—5´—三磷酸二钠盐(ATP-P)、β-甘油磷酸钠(β-P)、D-葡萄糖-6-磷酸二钠盐(G-6-P)和DIP)影响铜绿微囊藻砷代谢的总量与形态差异、水华蓝藻受磷与砷二者影响时的生长胁迫、磷含量与形态等进行全面、系统地研究。结果表明：1）水华蓝藻可单独以有机磷（DOP）β-P、G-6-P和ATP为磷源进行繁殖，其对DOP的适应性受其磷形态的影响而有所差异，β-P和G-6-P较DIP与ATP在短时间内更有利于藻细胞叶绿素a（Chla）的合成。2）不同磷环境下铜绿微囊藻对As(V)的耐受性表现为：DIP> G-6-P >β-P>ATP-P，藻体实际光能转化率（Yield）较光密度值（OD）和Chla能更好地表征不同磷源下As(V) 对藻细胞的胁迫响应。3）不同磷源下铜绿微囊藻对As(V)的吸收累积显著不同，表现为G-6-P较β-P和ATP-P更利于铜绿微囊藻胞内总砷的累积，G-6-P能显著促进铜绿微囊藻对As（V）的还原和后续的甲基化。4）不同形态磷介质中As(V)的存在不会影响铜绿微囊藻对DOP的转化， 但不同形态磷环境下DIP含量差异显著。5）非线性单室模型可较好描述藻体对As（V）的同步吸收和释放，高氮、低磷以及偏碱性的环境有利于水华蓝藻铜绿微囊藻对As（V）的有效累积及死亡后其在体内的保持。以上研究结果可促进磷对砷迁移转化作用的理解，提升对水环境中砷地球化学循环的理论认识，促进水环境砷污染潜在风险的管理水平。