Characterization of a Cr(VI)-sensitive Pseudomonas corrugata 28 mutant impaired in a pyridine nucleotide transhydrogenase gene

Bacteria are known to adopt complex metabolic strategies in an effort to counteract the impact of numerous toxic compounds. In this study, a Cr(VI)-sensitive mutant of the Cr(VI)-hyperresistant bacterium Pseudomonas corrugata 28, obtained by insertional mutagenesis using the EZ-Tn5™ Tnp, was employed to gain a greater understanding of Cr(VI) resistance in bacteria. The insertion of the transposon, which occurred 16 bp upstream from the start codon of an ORF encoding a soluble pyridine nucleotide transhydrogenase (STH), negatively affected expression of the sth gene. The compromised expression of the sth gene in the mutant had two main effects on the pyridine nucleotide pools: (i) a decrease in NADPH and NADH fractions with a consequent shift in the redox state toward oxidation; and (ii) a decrease in the total concentration of the pyridine nucleotides. In the absence of a suitable pool of NADPH, the mutant failed to sustain an effective defense against the oxidative stress induced by Cr(VI).