Tetrahymena thermophila: A whole cell biosensor for toxicity assessment of Mercury

Ciliated protozoans are ubiquitous, free living, and largely non-pathogenic microorganisms. Being single cell eukaryotic microorganisms they represent an essential component of all ecosystem where they are integral constituents of trophic chains and nutrient cycles (Foissner, 1987,1999, 2004; Darbyshire, 1994; Alpheiet al., 1996; Bonkowski and Schaefer, 1997; Sherr and Sherr, 2002; Cuvelieret al., 2010; Steele et al., 2011). They have been used as model organisms for the discovery of key genomic processes found across the eukaryotic tree of life, e.g., self-splicing RNAs, telomeres, and the role of RNAs in shaping germline and somatic genomes. Unlike bacteria, fungi they lack cell wall and are only separated from external environment via cell membrane, this makes them highly sensitive to any change in the environment. Considering that ciliated protozoa shows high similarity in the conserved genes (more than 800 human genes have orthologs in Tetrahymena and out of these 58 genes are associated with human diseases; Eisenet al., 2006;Fillinghamet al., 2002) between ciliates and several eukaryotes including humans, they represents a better biological tools to detect and diagnose communitylevel impairments in contaminated soil and water ecosystems. Thus, ciliate represents a perfect bioindicators that can be used for assessment of ecotoxicological assays for early warning deterioration of the environment. Furthermore, in response to heavy metal pollution, they express a special protein, i.e., metallothioneins (MT) rich in cysteine (cys) amino acid in which the thiol groups are able to bind heavy metals.Further, the induction of MTs by heavy metals is mainly regulated at transcription level.