The tellurite-resistance determinants tehAtehB and klaAklaBtelB have different biochemical requirements

Abstract

The tehAtehB operon from the Escherichia coli chromosome (32.3 min) mediates resistance to potassium tellurite (K, TeO, ) when expressed on a multicopy plasmid such as pUC8 (pTWT100). An MIC of 128 pg ml-l is observed when tehAtehB is expressed in a wild-type host and grown on rich media. In this study, the tehAtehB determinant was transformed into mutants deficient in electron transport processes andlor thiol redox coupling within E. coli. These mutants included ubi, nsd, cys, naf, trx, grx, gsh and sod. MlCs of tehAtehB transformed into these mutants ranged from 1-16 pg K, TeO, ml-l compared to 093-2 pg ml-l for strains transformed with a control plasmid. The telluriteresistance determinant locus M A cloned from the IncPa plasmid RK2Ter (pDT1558) was also investigated in these strains. This tellurite-resistance determinant showed little or no dependency on the host genotype. The ability of tehAtehB 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 M A determinant to mediate tellurite resistance was independent of medium conditions. These data suggest that either a reducing environment or electronreducing equivalents are required for tehAtehB 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.

Tellurite-mediated thiol oxidation in Escherichia coli

“…The dsbA and dsbB mutants gave MICs of 0n008-0n0015 µg K # TeO $ ml −" , which is the greatest degree of hypersensitivity observed to date, more than that observed for nitrate reductase mutants (MIC 0n03 µg K # TeO $ ml −" ) (Turner et al, 1995b). In contrast, mutants with defects in the other thiol : disulfide oxidoreductase pair dsbC and\or dsbD were not hypersensitive to tellurite.…”

“…Superoxide dismutase was also shown to be required. It is clear from that study that resistance mediated by the Te r determinants for the kilA locus and teh have different biochemical requirements (Turner et al, 1995b). The teh locus has a strict requirement for electron transport processes and\or thiol redox coupling whereas the kilA determinant showed no such dependency.…”

“…The procedure was performed as previously described (Turner et al, 1995b). Briefly, overnight cultures grown in LB broth were diluted to 10& cells ml − " and 10 µl aliquots were spotted onto LB agar plates containing serial dilutions of potassium tellurite (Sigma).…”

“…However, considerable insights have arisen in the understanding of tellurite biochemistry in E. coli. A study examining the resistance levels in metabolic mutants suggests that thiol redox enzymes (glutathione reductase and thioredoxin reductase) and their metabolites (thioredoxin, glutaredoxin and glutathione) are involved in tellurite resistance (Turner et al, 1995b). Superoxide dismutase was also shown to be required.…”

The major vault protein is related to the toxic anion resistance protein(TelA) family

“…For example, one of the earliest documented biological effects of tellurium poisoning is the demyelination of the sciatic nerve due to the inhibition of cholesterol biosynthesis and the accumulation of squalene in Schwann cells (Harry et al, 1989;Lampert et al, 1970). In bacteria, the toxicity of the soluble oxyanion tellurite, TeO 3 -2 , is thought to be due to its strong oxidizing effects on many enzymatic processes (Summers and Jacoby, 1977) and its ability to replace sulfur in metabolic reactions (Turner et al, 1995).…”