Tellurium, unlike the elements above it in the periodic table, is not thought to be required by biological systems. However, tellurium-resistant fungi grown in the absence of sulfur and in the presence of tellurite ions incorporated tellurium into amino acids and proteins (Ramadan et al, 1989). Tellurium is considered to be toxic to most organisms. Genes correlated with tellurium resistance have been identified, but the mechanisms of tellurium resistance are not completely understood (reviewed by Taylor, 1999).

Reduction of tellurite to insoluble elemental tellurium has been described in Gram-positive and Gram-negative bacteria and archaea, and is one mechanism of microbial tellurium resistance (reviewed by Chasteen and Bentley, 2003). Nitrate reductases (Sabaty et al, 2001) and terminal oxidases in the respiratory electron transport chain (Trutko et al, 2000) have been implicated in tellurium reduction. Biomethylation of tellurite, tellurate, and elemental tellurium to volatile dimethyltellurium has been observed in several species of bacteria and fungi, and may represent another mechanism of tellurium resistance (reviewed by Chasteen and Bentley, 2003).

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