Escherichia coli 6-phosphogluconate dehydrogenase aids in tellurite resistance by reducing the toxicant in a NADPH-dependent manner

Exposure to the tellurium oxyanion tellurite (TeO3 2−) results in the establishment of an oxidative stress status in most microorganisms. Usually, bacteria growing in the presence of the toxicant turn black because of the reduction of tellurite (Te4+) to the less-toxic elemental tellurium (Te0). In vitro, at least part of tellurite reduction occurs enzymatically in a nicotinamide dinucleotide-dependent reaction. In this work, we show that TeO3 2− reduction by crude extracts of Escherichia coli overexpressing the zwf gene (encoding glucose-6-phosphate dehydrogenase)takes place preferentially inthe presence of NADPH instead of NADH. The enzyme responsible for toxicant reduction was identified as 6-phosphogluconate dehydrogenase (Gnd). The gnd gene showed a subtle induction at short times after toxicant exposure while strains lacking gnd were more susceptible to the toxicant. These results suggest that both NADPHgenerating enzymes from the pentose phosphate shunt may be involved in tellurite detoxification and resistance in E. coli.