Artificial induction of cadmium tolerance and its further enhancement via heterologous co-expression of SpHMT1 and AtPCS1 in the yeast cells

Microorganisms can be used in the bioremediation of heavy metals. It is desirable if the microorganisms show a strong tolerance as well as the ability to accumulate (or biosorb) heavy metals. Yeast is well known for having a high capacity of biosorption of heavy metals. Therefore, the present study focused on developing a yeast mutant that has a strong tolerance to cadmium (Cd), a representative toxic metal. The Cd-resistant yeast mutant (CdR) was induced and isolated by growing yeast cells in media containing Cd and gradually increasing the concentration until reaching a possible maximum of 20 mM CdCl₂, to which the cells adapted and survived. CdR cells showed stronger tolerance to Cd-induced stress than the control cells. To obtain even higher Cd tolerance in the yeast cells, both Schizosaccharomyces pombe heavy metal tolerance factor 1 (SpHMT1) and Arabidopsis thaliana phytochelatin synthase (AtPCS1) genes were introduced into the CdR cells to be expressed simultaneously. The transformed CdR cells showed higher Cd tolerance than the untransformed CdR cells.