Sorption isotherm studies of Cd(II) ions using living cells of the marine microalga Tetraselmis suecica (Kylin) Butch

The present work reports the use of living cells of the marine microalga Tetraselmis suecica for the biosorption of cadmium ions. For a better understanding of the biosorption characteristics, three fractions of removed cadmium (total, bioadsorbed and intracellular) were measured in the cells after 24 and 72 h of exposure to different initial cadmium concentrations (0.6-45 mg L(-1)). Both the Langmuir and Freundlich models were suitable for describing the sorption of cadmium ions by this microalga. The maximum sorption capacity was estimated to be 40.22 mg Cd g(-1) after 72 h using the Langmuir sorption model. In the lower cadmium concentrations, metal removed intracellularly was higher than that removed on the microalgal cell surface. Therefore, the intracellular fraction contributed more to the total removed cadmium than the fraction bioadsorbed to the cellular surface. The results showed that the cadmium removal capacity using living biomass could be much more effective than with non-living biomass due to the intracellular bioaccumulation. According to the microorganism selected and its tolerance to the toxic effect of the metal, the cadmium content in the intracellular fraction can become very significant, just like it happened with Tetraselmis.

Dunaliella salina as marine microalga highly tolerant to but a poor remover of cadmium

Cadmium tolerance and removal in the marine microalga Dunaliella salina were studied in cultures exposed to different metal concentrations (5-120 mg Cd l(-1)) for 96h. This microalga can be included in the group of microalgal species most tolerant to cadmium due to the high value of EC50 that it possesses (48.9 mg Cd l(-1) at 96 h of culture). The greater percentage of cadmium removed was obtained in cultures exposed to 5 mg Cd l(-1) at 96h, but removing only 11.3% of the added cadmium. In all cultures, the quantity of cadmium removed intracellularly was much lower than the bioadsorbed quantity and it was proportional to the sulfhydryl group levels. Both the Freundlich and Langmuir adsorption models were suitable for describing the short-term biosorption of cadmium by living cells of D. salina.

Class III metallothioneins in response to cadmium toxicity in the marine microalga Tetraselmis suecica (Kylin) Butch

Microalgae are one of the most important organisms in our ecosystems being seriously affected by metal pollution. However, the microalgae Tetraselmis suecica (Kylin) Butch is tolerant to cadmium; the concentration of this metal that reduces the population growth to 50% of the control growth level is 5.8 mg/L after 96 h of exposure. In this study, class III metallothioneins were investigated for their involvement as a possible tolerance mechanism in this microalga when exposed to cadmium. A set of these molecules was purified from these microalgal cells after exposure to the metal. These polypeptides were analyzed by capillary zone electrophoresis, which is a technique that allows the length of the metallothioneins synthesized by this microalga to be known. The T. suecica cells were able to synthesize class III metallothioneins of three to six subunits of (gamma-Glu-Cys). The most abundant polypeptide possessed four subunits, and (gamma-Glu-Cys)6-Gly was the largest polypeptide synthesized by this microalga and detected by this technique. Tolerance to cadmium as a function of increasing polypeptide length is also discussed.