General Biological Role of Tellurium

Unlike selenium there is no required biological role for tellurium in bacteria or plants that has been determined however, this may ultimately not be the whole story. Selenium was only viewed as a toxic metalloid with no necessary role for metabolism until at least the 1950s see above. While tellurite is less soluble than tellurate in aqueous solution, in general tellurite is probably more toxic to most organisms. The non Te-resistant wild type E. coli bacterium (Gramnegative) has MICs of 1 to 3 ppm for tellurite and tellurate. Tellurite is used to enrich and select for Staphylococcus UMre 5.  

In experiments parallel to those of Cowie and Cohen (see above), a Te-resistant fungi grown in high tellurite amendments with little available sulfur produced telluromethionine, tellurocysteine, and tellurocystine.So like selenium, tellurium can apparently substitute for sulfur under certain 

The meehanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role. A few tellurite determinants - both ehromosomal and plasmid eneoded - have been identified in bacte-Reeent studies have focused on the role of methyltransf-erases in Te resistanee. Liu et al determined that the E. coli gene tehB uses 5 -adenosylmethionine and a methyltransferase in tellurite detoxifieation, but while no methylated tellurium eompounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred. 

Like selenium, the proeess of reduetion/oxidation cycling in biological systems is important and ehanges in the oxidation state are often an easy means of determining bioreduetion for added tellurium oxyanions. The general order of 

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