The Oceanography and Biochemistry of Cadmium

虽然镉通常被认为是一种有毒元素，但它是由生物群从海洋表面清除出来的，并被合并到有机物质中，在深水中沉淀并重新矿化。最近的数据表明，Cd实际上是一种微量营养素，在许多海洋浮游植物中有效地替代了锌。在海洋硅藻中，Cd取代了锌作为碳酸酐酶(CA)中的金属中心，CA参与了光合作用中获取无机碳的过程。Cd也被球藻利用，但这些生物中的生化功能尚不清楚。在这项研究中，普林斯顿大学的一位研究人员将基于一个普遍的假设，即Cd的海洋循环是由于浮游植物在低环境锌浓度下将其作为微量营养素利用而导致的。初步证据表明，Cd可能是碱性磷酸酶(AP)的金属中心，AP是一种参与从有机磷中获取磷的酶。利用新的实验室实验，科学家将确定这种生物体中的主要CD酶，首先假设CD-AP可能是这样一种酶。对不同物种中编码CD酶的DNA序列的研究将揭示这些酶在微藻中的多样性，并确定共同的寡核苷酸，以在野外样本中确定相应的DNA和RNA序列。Cd酶的合成(及其对环境条件的反应)的间接证据将通过沿自然化学梯度的关键元素和化合物(例如，颗粒态Cd、溶解的CO2和PO4)的分析以及在必要时修改的自然样品的船上培养来提供。将通过应用实验室开发的分子工具，使用免疫检测、DNA样本的聚合酶链式反应和RNA样本的逆转录聚合酶链式反应，寻找CD酶的直接证据和量化。该项目的成功完成不仅将解释控制Cd海洋地球化学的过程，证明Cd作为一种微量营养素的重要性，还将为在沉积CaCO3中利用Cd作为过去营养浓度的古指示剂提供机制基础，而且还将导致发现新的金属酶，并为硅藻和球藻的生态提供新的见解。

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.