Relationships between cell-specific growth rate and uptake rate of cadmium and zinc by a coastal diatom

Despite the fact that the influence of metal chemistry on metal uptake in marine phytoplankton has been well studied, the effects of physiological processes such as cellular growth remain less well known. In this study, the cell-specific growth rate of the coastal diatom Thalassiosira pseudonana (Clone-3H) was modified by 3 environmental factors: temperature, irradiance, and the light-dark (LD) cycle. Uptake of Cd and Zn was subsequently quantified using short-term exposure. These environmental factors significantly affected metal uptake. Cd and Zn uptake rates increased with increasing irradiance, temperature, and illumination period. We demonstrate that the metal uptake rate initially increased in proportion with an increase in cell-specific growth rate, and then remained constant. Uptake of Cd and Zn by the diatoms was not affected by 2 photosynthetic inhibitors, suggesting that their uptake was not affected by the photosynthetic activity. There was no obvious diel trend for metal uptake. Thus in this study, cell size, photosynthetic activity, and cell cycle were unlikely to have accounted for the variations in metal uptake at different temperatures, irradiances, and LD cycles. The dependence of metal uptake on cell-specific growth rate may have important implications for the prediction of metal accumulation by marine phytoplankton in different ecosystems or during phytoplankton blooms. Further studies are needed to examine the underlying mechanisms for such relationships at cellular and subcellular levels.