Cellular composition and physiological characteristics of the diatom Thalassiosira weissflogii adapted to cadmium stress

Prolonged exposure of Thalassiosira weissflogii (Grunow) to a sub-lethal concentration of cadmium in continuous culture resulted in the development of cellular characteristics allowing optimal growth in the presence of Cd. Examination of Cd-adapted and unadapted cells was made on steady-state populations growing at the same rate in order to eliminate any effects of differing growth rate on metabolism. Adaptation to Cd stress was manifested as increases in mean cell volume, dry weight, protein: DNA, protein: RNA, protein: carbohydrate, protein nitrogen: total cell nitrogen and carotenoid: chlorophyll a ratios. Subsequent exposure of the cells to Cd over a wide concentration range showed that cellular division rate, carbon photoassimilation and extracellular release of dissolved organic compounds were greatest near the Cd concentration to which the cells had previously been adapted. Enhanced cellular carbon photoassimilation in Cd-adapted cells correlated exactly with increased cellular protein content. The amount of dissolved organic excretion by Cd-adapted cells at the adaptation concentration was the same as that of unadapted cells at the same concentration. Since total carbon photoassimilation was greater in Cd-adapted cells at this concentration, the percentage of carbon excreted was less in these cells.