Kinetics of uptake and intracellular location of cobalt, manganese and zinc in the estuarine green alga Chlorella salina

Abstract

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.

Genotoxicity of cadmium in marine diatom Chaetoceros tenuissimus using the alkaline Comet assay

“…The inhibitory effects above 7.5 mg/L concentrations were further confirmed by the LSD values (P<0.01). Similar patterns have been obtained by Torres et al (1998) while studying the removal of Cd ions by the marine diatom Phaeodactylum tricornutum; and Garnham et al (1992) while studying uptake and intracellular location of cobalt, manganese and zinc in the estuarine green alga Chlorella salina.…”

Influence of Cellular Density on Determination of EC50 in Microalgal Growth Inhibition Tests

“…It is demonstrated that there are two phases in metal adsorption by microalgae: a "rst phase, nondependent on cellular metabolism, where metal binds to the cellular surface (adsorption), and a second, slower phase dependent on metabolism, where metal is accumulated in the interior of the cell (absorption) (Garnham et al, 1992;Moreno-Garrido et al, 1998). The amount of metal adsorbed seems to be much higher than metal absorbed in living cells (Sakaguchi et al, 1979;Moreno-Garrido et al, 1998).…”

Transport kinetics, cation inhibition and intracellular location of accumulated caesium in the green microalga Chlorella salina

“…Differential extraction techniques have been used to determine solute levels in different cellular compartments (Huber-Walchli & Wiemken, 1979;White & Gadd, 1987) and their use has recently been extended to microalgae. Garnham et al (1992) observed higher concentrations of Co2+, Mn2+ and Zn2+ in the vacuoles than in the cytoplasm of the microalga Chlorella salina, although due to the small fraction of the cellular volume occupied by the vacuoles of this organism, total metal levels were higher in the cytoplasm.…”