Transition metals affect the viability of organisms and are fundamental and limiting factors at the same time, since they represent nutritionally important yet cytotoxic components in our environment. Both prokaryotes and eukaryotes carry cellular systems to maintain the metal homeostasis.Metallothioneins (MTs) are 6-7 kDa, ubiquitous, cytoplasmic, cysteine rich proteins, which have the capacity of high affinity binding to heavy metal ions. MTs play key role in essential as well as toxic heavy metal metabolism in the organisms. The ciliates tolerate elevated concentrations of metals, which...