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Tellurite exerts a deleterious effect on a number of small molecules containing sulfur moieties that have a recognized role in cellular oxidative stress. Because cysteine is involved in the biosynthesis of glutathione and other sulfur-containing compounds, we investigated the expression of Geobacillus stearothermophilus V cysteine-related genes cobA, cysK, and iscS and Escherichia coli cysteine regulon genes under conditions that included the addition of [K.sub.2]Te[O.sub.3] to the culture medium. Results showed that cell tolerance to tellurite correlates with the expression level of the cysteine metabolic genes and that these genes are up-regulated when tellurite is present in the growth medium.

The authors review the publications on biological methylation. The topics of interest include bioalkylation, metalloids' methylation, arsenic methylation, antimony biomethylation and enzymology of biomethylation.

The purple nonsulfur bacterium Rhodobacter sphaeroides converts selenate and selenite into organic forms and the red elemental form. Very little is produced in volatile form.

A fast, simple and reliable chemical method based on the NaB[H.sub.4]-mediated reduction of Te[O.sub.3.sup.2-] followed by the spectrophotometric determination of elemental tellurium in solution is used for tellurite quantification. The method is found to be highly reproducible and is stable at different pH values and exhibits linearity over a broad range of tellurite concentrations.