THE TELLURITE-RESISTANCE DETERMINANTS TEHATEHB AND KLAAKLABTELB HAVE DIFFERENT BIOCHEMICAL REQUIREMENTS

The tehAtehB operon from the Escherichia coli chromosome (32.3 min) me diates resistance to potassium tellurite (K2TeO3) when expressed on a multicopy plasmid such as pUC8 (pTWT100). An MIC of 128 mu g ml(-1) is observed when tehAtehB is expressed in a wild-type host and grown on rich media. In this study, the tehAtehB determinant was transformed in to mutants deficient in electron transport processes and/or thiol redo x coupling within E. coli. These mutants included ubi, nad, cys, nar, trx, grx, gsh and sod. MICs of tehAtehB transformed into these mutants ranged from 1-16 mu g K2TeO3 ml(-1) compared to 0.03-2 mu g ml(-1) fo r strains transformed with a control plasmid. The tellurite-resistance determinant locus kilA cloned from the IncP alpha plasmid RK2Te(r) (p DT1558) was also investigated in these strains. This tellurite-resista nce determinant showed little or no dependency on the host genotype. T he ability of tehAtehB to mediate resistance in wild-type hosts is lim ited to rich medium. Rich medium may provide a key unidentified cofact or required by TehATehB that is not provided under minimal conditions. Again, the ability of the kilA determinant to mediate tellurite resis tance was independent of medium conditions. These data suggest that ei ther a reducing environment or electron-reducing equivalents are requi red for tehAtehB to mediate high levels of resistance to potassium tel lurite. Therefore, the two resistance determinants studied here posses s two very different biochemical mechanisms of resistance. Our data al so suggest a mechanism for endogenous resistance to tellurite which in volves nitrate reductase, superoxide dismutase, and thiol redox proces ses.