The Oceanography and Biochemistry of Cadmium

Princeton University, Princeton NJ

Investigators

Abstract

ABSTRACT OCE- 0351499 Although 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.