The operon from the chromosome (32.3 min) mediates resistance to potassium tellurite (KTeO) when expressed on a multicopy plasmid such as pUC8 (pTWT100). An MIC of 128 μg mlis observed when is expressed in a wild-type host and grown on rich media. In this study, the determinant was transformed into mutants deficient in electron transport processes and/or thiol redox coupling within . These mutants included and MICs of transformed into these mutants ranged from 1-16 μg KTeO mlcompared to 0.03-2 μg mlfor strains transformed with a control plasmid. The tellurite-resistance determinant locus cloned from the IncPα plasmid RK2Te(pDT1558) was also investigated in these strains. This tellurite-resistance determinant showed little or no dependency on the host genotype. The ability of to mediate resistance in wild-type hosts is limited to rich medium. Rich medium may provide a key unidentified cofactor required by TehATehB that is not provided under minimal conditions. Again, the ability of the determinant to mediate tellurite resistance was independent of medium conditions. These data suggest that either a reducing environment or electron-reducing equivalents are required for to mediate high levels of resistance to potassium tellurite. Therefore, the two resistance determinants studied here possess two very different biochemical mechanisms of resistance. Our data also suggest a mechanism for endogenous resistance to tellurite which involves nitrate reductase, superoxide dismutase, and thiol redox processes.


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