Effects of decreased specific glutathione reductase activity in a chromate-tolerant mutant of Schizosaccharomyces pombe

Abstract

A chromate-tolerant mutant chr1-663T bearing a stable one-gene mutation and its parental strain 6chr(+) were used to investigate the background of Cr(VI) tolerance in the fission yeast Schizosaccharomyces pombe. The mutant chr1-663T displayed a significantly decreased specific glutathione reductase (GR) activity coded by the pgr1 (+) gene compared with its parental strain. Transformants of the mutant chr1-663T with a nonintegrative pUR18N vector expressing the pgr1 (+) gene exhibited the same Cr(VI) sensitivity and specific GR activity as their parental strain, demonstrating the importance of the GR-NADPH system in Cr(VI) tolerance. Transformants, nevertheless, exhibited an increased intracellular peroxide concentration, a decreased Cr(VI)-reducing and HO*-producing ability, which suggested an unbalanced oxidoreduction state of cells and partial complementation of the GR function. No mutation was found in the sequences of the pgr1 (+) and the pap1 (+) (transcriptional regulatory gene of GR) genes of the Cr(VI)-tolerant mutant by sequence analysis.

Molecular mechanisms of Cr(VI) resistance in bacteria and fungi

“…When the mutant was transformed with a vector carrying a glutathione reductase, it recovered the parental susceptibility level, losing the tolerant phenotype. This finding underlines the importance of the GSH reductase-NADPH system in Cr(VI) as a major one-electron donor for reduction reactions (Gazdag et al, 2003;Koosz et al, 2008). On the other hand, in S. cerevisiae GSH does not appear to be involved in the tolerance to chromium and other metals, although it could play a role in Cr(VI) uptake (Gharieb & Gadd, 2004).…”

“…When the mutant was transformed with a vector carrying a glutathione reductase, it recovered the parental susceptibility level, losing the tolerant phenotype. This finding underlines the importance of the GSH reductase‐NADPH system in Cr(VI) as a major one‐electron donor for reduction reactions (Gazdag et al ., ; Koosz et al ., ). On the other hand, in S .…”

Hexavalent molybdenum reduction to Mo-blue by Acinetobacter calcoaceticus

“…The high optimum temperature suggests that the bacterium should be useful in a tropical climate like Malaysia where normal soil temperatures could reach as high as 35 °C (Sinnakkannu et al 2004). In other similar works on the biological reduction of Cr(VI), the requirement of near-neutral pH and a moderate temperature range is shared by many chromate-reducing bacteria (Horitsu et al 1978;Gvozdyak et al 1986;Hardoyo et al 1991;Rege et al 1997;Koósz et al 2008).…”

Adaptation to tert‐butyl hydroperoxide at a plasma membrane level in the fission yeast Schizosaccharomyces pombe parental strain and its t‐BuOOH‐resistant mutant

“…. The ura4‐D18 h − auxotrophic, heterothallic strain of S. pombe , designated hyd + , was used to isolate t ‐BuOOH‐resistant mutants because of its suitability for transformation experiments with the non‐integrative multi‐copy pUR18N vector to identify the gene responsible for the resistance observed . Briefly, parallel cultures of hyd + were exposed to stepwise increasing concentrations of t ‐BuOOH (0.5–4 mM) in minimal SM liquid medium containing 1% glucose, 0.5% (NH 4 ) 2 SO 4 , 0.05% KH 2 PO 4 , 0.01% MgSO 4 , and 0.01% Wickerham's vitamin solution supplemented with 100 mg L −1 uracil at pH 4.5.…”