Biopolymers as carrier phases for selected natural radionuclides (of Th, Pa, Pb, Po, Be) in diatoms and coccolithophores

生物聚合物作为硅藻和颗石藻中选定天然放射性核素（Th、Pa、Pb、Po、Be）的载体相

• 批准号: 1356453
• 负责人: Peter Santschi
• 金额: $ 50.68万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-01 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1356453&HistoricalAwards=false
• 关键词: Biopolymers; carrier; phases; selected; natural

Particle-associated natural radioisotopes are transported to the ocean floor mostly via silica and carbonate ballasted particles, allowing their use as tracers for particle transport. Th(IV), Pa (IV,V), Po(IV), Pb(II) and Be(II) radionuclides are important proxies in oceanographic investigations, used for tracing particle and colloid cycling, estimating export fluxes of particulate organic carbon, tracing air-sea exchange, paleoproductivity, and/or ocean circulation in paleoceanographic studies. Even though tracer approaches are considered routine, there are cases where data interpretation or validity has become controversial, largely due to uncertainties about inorganic proxies and organic carrier molecules. Recent studies showed that cleaned diatom frustules and pure silica particles, sorb natural radionuclides to a much lower extent (by 1-2 orders of magnitude) than whole diatom cells (with or without shells). Phytoplankton that build siliceous or calcareous shells, such as the diatoms and coccolithophores, are assembled via bio-mineralization processes using biopolymers as nanoscale templates. These templates could serve as possible carriers for radionuclides and stable metals. In this project, a research team at the Texas A & M University at Galveston hypothesize that radionuclide sorption is controlled by selective biopolymers that are associated with biogenic opal (diatoms), CaCO3 (coccolithophores) and the attached exopolymeric substances (EPS), rather than to pure mineral phase. To pursue this idea, the major objectives of their research will include separation, identification and molecular-level characterization of the individual biopolymers (e.g., polysaccharides, uronic acids, proteins, hydroquinones, hydroxamate siderophores, etc.) that are responsible for binding different radionuclides (Th, Pa, Pb, Po and Be) attached to cells or in the matrix of biogenic opal or CaCO3 as well as attached EPS mixture, in laboratory grown diatom and coccolithophore cultures. Laboratory-scale radiolabeling experiments will be conducted, and different separation techniques and characterization techniques will be applied. Intellectual Merit : It is expected that this study will help elucidate the molecular basis of the templated growth of diatoms and coccoliths, EPS and their role in scavenging natural radionuclides in the ocean, and help resolve debates on the oceanographic tracer applications of different natural radioisotopes (230,234Th, 231Pa, 210Po, 210Pb and 7,10Be). The proposed interdisciplinary research project will require instrumental approaches for molecular-level characterization of these radionuclides associated carrier molecules.Broader Impacts: The results of this study will be relevant for understanding biologically mediated ocean scavenging of radionuclides by diatoms and coccoliths which is important for carbon cycling in the ocean, and will contribute to improved interpretation of data obtained by field studies especially through the GEOTRACES program. This new program will enhance training programs at TAMUG for postdocs, graduate and undergraduate students. Lastly, results will be integrated in college courses and out-reach activities at Texas A&M University, including NSF-REU, Sea Camp, Elder Hostel and exhibits at the local science fair and interaction with its after-school program engaging Grade 9-12 students from groups traditionally underrepresented.

与粒子相关的天然放射性同位素主要通过二氧化硅和碳酸盐压载粒子被输送到海底，这使得它们可以作为粒子输送的示踪剂。Th(IV), Pa (IV，V), Po(IV), Pb（II）和Be（II）放射性核素是海洋调查中的重要代用物，在古海洋研究中用于追踪颗粒和胶体循环，估计颗粒有机碳的输出通量，追踪海气交换，古生产力和/或海洋环流。尽管示踪剂方法被认为是常规的，但在某些情况下，数据解释或有效性已成为争议性的，主要是由于无机代用物和有机载体分子的不确定性。最近的研究表明，与完整的硅藻细胞（带壳或不带壳）相比，清洁过的硅藻小体和纯二氧化硅颗粒吸收天然放射性核素的程度（低1-2个数量级）要低得多。硅藻和球石藻等能够形成硅质或钙质外壳的浮游植物，是通过生物矿化过程将生物聚合物作为纳米级模板组装而成的。这些模板可以作为放射性核素和稳定金属的可能载体。在这个项目中，加尔维斯顿德克萨斯a & M大学的一个研究小组假设，放射性核素的吸收是由选择性生物聚合物控制的，这些生物聚合物与生物蛋白石（硅藻）、CaCO3（球石藻）和附着的外聚合物（EPS）有关，而不是纯矿物相。为了实现这一想法，他们的主要研究目标将包括分离、鉴定和分子水平表征个体生物聚合物（如多糖、醛酸、蛋白质、对苯二酚、羟肟酸铁载体等），这些生物聚合物负责结合不同的放射性核素（Th、Pa、Pb、Po和Be），这些放射性核素附着在细胞上，或附着在生物蛋白石或CaCO3基质中，以及附着的EPS混合物中，在实验室培养的硅藻和球石藻培养中。将进行实验室规模的放射性标记实验，并应用不同的分离技术和表征技术。知识价值：本研究将有助于阐明硅藻、球藻、EPS模板生长的分子基础及其在海洋中清除天然放射性核素的作用，并有助于解决不同天然放射性同位素（230,234,231Pa, 210Po， 210Pb和7,10be）海洋示踪剂应用的争论。拟议的跨学科研究项目将需要用仪器方法对这些放射性核素相关载体分子进行分子水平表征。更广泛的影响：本研究的结果将有助于理解硅藻和球石对海洋放射性核素的生物介导清除作用，这对海洋中的碳循环很重要，并将有助于改进对实地研究，特别是通过GEOTRACES项目获得的数据的解释。这个新项目将加强TAMUG对博士后、研究生和本科生的培训项目。最后，研究结果将整合到德州农工大学的大学课程和外展活动中，包括NSF-REU、海上夏令营、老年旅馆、当地科学博览会的展览，以及与学校的课外项目互动，这些项目吸引了9-12年级的学生，这些学生来自传统上代表性不足的群体。