Biochemical and biophysical analysis of plasmid pMJ600-encoded tellurite [TeO2(3-)] resistance

Escherichia coli AB1157, and the transconjugant AB1157 (pMJ600), were used to study the mechanism of tellurite resistance conferred by pMJ600, which contains the tellurite resistance determinant cloned from the IncHI-2 conjugative plasmid pMER610. The transconjugant can tolerate a 100-fold higher concentration of potassium tellurite [K2TeO3] than the plasmid-free strain. Both strains were found to accumulate tellurite irreversibly at equivalent rates, with elemental tellurium being deposited intracellularly, direct efflux of tellurite was not found to contribute to the resistance mechanism. However, under these conditions, growth, protein synthesis and oxygen uptake ceased in AB1157, but-were unaffected in the transconjugant. No NADH- or NADPH-linked reduction of tellurite was detected in crude cell extracts of either strain; however, cell extracts of both reduced tellurite at alkaline pH in the absence of any co-factors.