The Oceanography and Biochemistry of Cadmium

虽然镉通常被认为是一种有毒元素，但它会被海洋生物从海洋表面清除，并结合到沉积在深水中的有机物质中。最近的数据表明，镉实际上是一种微量营养元素，有效地替代锌在许多种海洋浮游植物。在海洋硅藻，占主导地位的沿海和上升流沃茨，镉的碳酸酐酶（CA），参与无机碳的光合作用的收购酶的金属中心锌的替代品。在这项研究中，来自普林斯顿大学的研究人员将阐明负责海水中的镉（Cd）的循环过程的一般假设的基础上，镉的海洋循环的结果，它作为一种微量营养元素的浮游植物在低环境Zn浓度下的利用。 初步证据表明，镉可能作为一个金属中心的碱性磷酸酶（AP），参与收购有机磷酸盐的磷酶。 使用新的实验室实验与模型coccolithophore Emiliana huxleyi，科学家将确定主要的CD酶在这种生物体，从假设Cd-AP可能是这样的酶。 研究的DNA序列编码的镉酶在不同的物种将揭示这些酶之间的微藻的多样性，并确定共识寡核苷酸，以确定相应的DNA和RNA序列在现场样品。 通过分析关键元素和化合物（例如，颗粒Cd、溶解的CO2和PO 4）沿着天然化学梯度和在船上培养的天然样品中进行必要的修正。直接的证据和量化的镉酶将寻求在实验室中开发的分子工具的应用，使用免疫检测，PCR的DNA样品和RNA样品的逆转录PCR。 该项目的成功完成不仅将解释控制海洋镉地球化学的过程，记录镉作为微量营养元素的重要性，并为利用沉积碳酸钙中的镉作为过去营养元素浓度的古指示剂提供机理基础，而且还将导致发现新的金属酶，并为硅藻和颗石藻的生态学提供新的见解。

ABSTRACTOCE- 0351499Although it is generally considered a toxic element, cadmium is scavenged from the ocean surface by the biota and incorporated into the organic material that settles and is remineralized in deep water. Recent data demonstrate that Cd is in fact a micronutrient that substitutes effectively for Zn in many species of marine phytoplankton. In marine diatoms, which dominate coastal and upwelling waters, Cd substitutes for Zn as the metal center in carbonic anhydrase (CA), an enzyme involved in the acquisition of inorganic carbon for photosynthesis. Cd is also utilized by coccolithophores, which flourish in oligotrophic gyres, but the biochemical function in these organisms is unknown.In this study, a researcher from Princeton University will elucidate the processes responsible for the cycling of cadmium (Cd) in seawater based on the general hypothesis that the oceanic cycling of Cd results from its utilization as a micronutrient by phytoplankton under low ambient Zn concentration. Preliminary evidence indicates that Cd may serve as a metal center in alkaline phosphatase (AP), an enzyme involved in the acquisition of phosphorus from organic phosphate. Using new laboratory experiments with the model coccolithophore Emiliana huxleyi, the scientist will identify the principal CD enzymes in this organism, starting with the hypothesis that Cd-AP may be such an enzyme. Studies of the DNA sequences coding for Cd enzymes in various species will reveal the diversity of these enzymes among microalgae and identify consensus oligonucleotides to identify corresponding DNA and RNA sequences in field samples. Indirect evidence for the synthesis of Cd enzymes (and of its response to environmental conditions) will be provided by analysis of key elements and compounds (e.g., particulate Cd, dissolved CO2 and PO4) along natural chemical gradients and in on-board incubations of natural samples amended as necessary. Direct evidence and quantification of the Cd enzymes will be sought by application of the molecular tools developed in the laboratory, using immunodetection, PCR of DNA samples and reverse transcription PCR of RNA samples. The successful completion of this project will not only explain the processes that control the oceanic geochemistry of Cd, document the importance of Cd as a micronutrient, and provide a mechanistic basis for the utilization of Cd in sedimentary CaCO3 as a paleo-indicator of past nutrient concentrations, but also lead to the discovery of novel metallo-enzymes and provide new insights into the ecology of diatoms and coccolithophores.