Percent activity of organic fractions from diatoms that bind with radionuclide

<p>Percent amount of organic fractions from diatoms that bind with radionuclide. In order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides 234Th, 233Pa, 210Pb, and 7Be during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (nonattached and attached exopolymeric substances), intracellular (ethylene diamine tetraacetic acid and sodium dodecyl sulfate extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, Uronic acids showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance analyses, the frustule BF were mainly composed of carboxyl-rich, aliphatic-phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom-associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom-related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean.</p> <p>&nbsp;</p>可与放射性核素（radionuclide）结合的硅藻源性有机组分的百分占比。为探究与生物成因二氧化硅（biogenic silica）结合的生物聚合物（biopolymer）在放射性核素清除过程中的重要性，本研究将三角褐指藻（Phaeodactylum tricornutum）在其生长阶段与放射性核素234Th、233Pa、210Pb及7Be共培养。研究测定了结合于不同有机化合物类别（即蛋白质、总碳水化合物、糖醛酸（uronic acid））的放射性核素的归一化亲和系数，这些有机组分分别提取自胞外（游离与附着的胞外聚合物（exopolymeric substances, EPS））、胞内（乙二胺四乙酸（ethylene diamine tetraacetic acid, EDTA）与十二烷基硫酸钠（sodium dodecyl sulfate, SDS）可提取组分）以及硅质壳（frustule）包埋的生物聚合物组分（BF）。结果显示，放射性核素主要富集于硅质壳包埋的生物聚合物组分中。在测定的三类有机组分中，糖醛酸对所有受试放射性核素均表现出最强的结合亲和性。经分光光度法（spectrophotometry）与二维异核单量子相干核磁共振（two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance, 2D HSQC-NMR）分析证实，硅质壳包埋的生物聚合物组分主要由富羧基脂肪族磷蛋白构成，这类物质可能是多数放射性核素强结合作用的关键介导因子。本研究结果为不同种类的硅藻相关生物聚合物以协同而非单一化合物的方式介导放射性核素选择性吸附提供了证据。该发现明确揭示了这类硅藻相关生物聚合物，尤其是硅质壳生物聚合物，在海洋中作为粒子示踪剂（particle tracer）的放射性核素清除与分馏过程中的重要性。