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.