Abstract
Coccolithophorids are unicellular marine algae that produce CaCO3 crystals on the cell surface and therefore very important for fixing large amount of carbon by both photosynthesis and calcification. We previously found that nanomolar level of selenium is essential for growth of coccolithophorids. In this study, we investigated on the utilization mechanism of selenium by a coccolithophorid, Emiliania huxleyi, by means of kinetic analysis of Se-uptake using 75Se-radiolabelled selenite.
The intracellular concentration of Se increased 2400-fold where the initial concentration of Se in the medium was 3.2-nM (seawater-level). 50% and 20% of Se incorporated by cells were fixed into low-molecular-mass-compounds and proteins, respectively. Kinetic analyses of 75Se-uptake in experiments with inhibitors for energy production revealed that Se-concentrating mechanism involves two steps: namely, rapid uptake of selenite by the combination of active and passive transport systems and subsequent synthesis and accumulation of Se-containing organic compounds, such as amino acid derivatives and proteins.
