The uptake kinetics and intracellular location of cobalt (6°C0), manganese (SaMn) and zinc (65Zn) have been characterized in Chlorella salina. Uptake of all three metals was biphasic. The initial rapid phase was independent of light, temperature or the presence of metabolic inhibitors. This first phase of metabolismindependent biosorption was followed by a slower phase of uptake that was apparently dependent on metabolism and decreased by incubation in the dark, or in the light at low temperature or in the presence of metabolic inhibitors. This latter phase of metal accumulation followed Michaelis-Menten kinetics. However, when expressed in the form of a Lineweaver-Burk plot two distinct phases were apparent for each metal with the following Km values (lXM); Co 2+, 19 and 266; Mn 2÷, 2 and 760; Zn 2+, 4 and 635. For all three metals cellular compartmentation analysis showed that large amounts of metal were bound to intracellular components and to the cell wall. There was also a higher concentration of each metal in the vacuole than in the cytosol, indicating transport of the metals across the tonoplast which may, in part, account for the multi-phasic uptake systems detected. The influence of competing divalent ions on the active uptake of Co 2+ and Mn 2+ was also studied. When the concentration of divalent ion was the same as that of Co 2+ the uptake of the latter was not affected, indicating a specific system for the uptake of Co 2+. However, Mn 2+ uptake was inhibited by Mg 2+, Zn 2+ and Cd 2+, but not by Co 2+, which indicated that Mn 2+, Mg 2+, Zn 2+ and Cd 2+ may enter the cells via a common system with different affinities for each metal.

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Accumulation of cobalt and cesium by the microalga Scenedesmus obliquus and the cyanobacterium Synechocystis PCC 6803 has been characterized at metal concentrations ranging from 1-100 µM in the presence of three clay minerals, montmorillonite, illite, and kaolinite. The majority of metal uptake over a 4 h period consisted of rapid binding to the clay mineral-cell aggregates, and was unaffected by incubation in the dark or by the presence of the metabolic inhibitor carbonyl cyanide-3-chlorophenyl hydrazone (CCCP). This was followed by a slower, energy-dependent uptake of metal by the cell components of the mixtures, which was inhibited by incubation in the dark or in the presence of CCCP. The initial phase of uptake by the clay mineral-cell mixtures and mixture components alone conformed to a Freundlich adsorption isotherm, the order of uptake for both cobalt and cesium being montmorillonite-cells > illite-cells > kaolinite-cells. S. obliquus-clay mineral mixtures accumulated more cobalt and cesium than Synechocystis PCC 6803-clay mineral mixtures. On a dry weight basis, clay minerals alone accumulated greater amounts of metals than clay mineral-cell mixtures, which accumulated more than the cells alone. However, when the same data was expressed as amount of metal adsorbed per unit surface area, S. obliquus, in most cases, adsorbed greater amounts of cobalt and cesium than the clay minerals or Synechocystis PCC 6803. As the proportion of clay in a cell-clay mineral mixture was increased, the amount of metal accumulated also increased. Reduced accumulation of cobalt and cesium by cell-clay mineral mixtures, exhibited by equal amounts of the individual components added together, indicated that the formation of clay-cell aggregates had masked some of the binding sites normally available to metal ions. Accumulation of cobalt and cesium by all clay mineral-cell mixtures was dependent on the external pH and NaCl concentration, and decreased with decreasing pH and increasing external NaCl concentration.