Predicting cadmium toxicity with the kinetics of phytochelatin induction in a marine diatom

Phytochelatin (PC) synthesis is thought to be a rapid and specific response to metal exposure in marine phytoplankton, but its potential as a predictor of metal toxicity is far from conclusive. Thus this research examines the bioaccumulation, PC induction, and toxicity of Cadmium (Cd) in Thalassiosira weissflogii, a coastal diatom under varying nutrient conditions. Nitrogen limitation strongly inhibited Cd uptake and PC induction at the same [Cd²⁺] level, and increased metal sensitivity. Conversely, phosphorus limitation had little influence on Cd accumulation and PC induction, yet also enhanced metal effect on growth. Differential growth inhibitions were correlated with [Cd²⁺], intracellular Cd concentration, PC concentration, the kinetics of Cd uptake and PC induction, respectively. It was found that stronger interrelations existed between kinetic rates (both Cd uptake and PC synthesis) and Cd sensitivity than between the static concentrations (Cd and PC) and growth inhibition. Moreover, according to the calculated median inhibition concentration (IC50), median effective uptake rate of Cd, as well as median effective induction rate of PCs, the latter two showed the smallest variation when nutrients were varied (1.4-1.9 fold). Our study set out the first step toward considering the use of PC synthesis kinetics to predict metal toxicity for phytoplankton.