Glutathione Relevance in the Response of Ciliate Tetrahymena thermophila Against Metals/Metalloids and Other Environmental Stressors

The tripeptide glutathione (GSH) is the primary and most abundant non-protein thiol compound present in all aerobic organisms. The main function of this molecule is cellular antioxidant defense. For the first time in ciliates, using the eukaryotic microorganism Tetrahymena thermophila as a model organism, several parameters (cell mortality, molecules containing −SH groups, and total glutathione) have been evaluated under the toxic effects of various chemical stressors (including several metals/metalloids), either in combination with or without the inhibitory effects of BSO (a GSH biosynthesis inhibitor) or NEM (an inhibitor of molecules containing −SH groups). Oxidative stress caused by many of these stressors is mitigated jointly by GSH and molecules containing −SH groups (such as metallothioneins). Likewise, it requires the over-expression of GR (glutathione reductase) and GCL (glutamate cysteine ligase) genes. Bioinformatic and phylogenetic analysis of these enzymes, involved in the reduction in oxidized glutathione and in its biosynthesis, confirms their correct identification, evolutionary conservation and clustering with the taxonomic group of the ciliate species to which they belong.