Oxidative Stress, Chromium-Resistance and Uptake by Fungi: Isolated from Industrial Wastewater

Trichosporon asahii and Rhodotorula mucilaginosa isolated from wastewater effluents were identified as chromium-resistant yeasts. Cr(VI) concentrations at 8 mM and 6 mM were inhibitory for R. mucilaginosa and T. asahii. Remarkably elevated GSH (69.88 +/- 10.01) and GSSG (11.24 +/- 0.96) was observed under metal stress in T. asahii as compared to R. mucilaginosa GSH (18.95 +/- 3.19) and GSSG (3.7 +/- 2.74) mM g-1 8 level. Statistical analysis revealed significantly higher GSH/GSSG ratio in both strains. NPSH (29.84 +/- 0.54) level in T. asahii was much higher than in R. mucilaginosa (6.05 +/- 0.24). Chromate reductase (ChR) was assayed and its activity was optimum at 50 degrees C (pH 6) in T. asahii while R. mucilaginosa showed higher activity at 30 degrees C (pH 7). Activity of both ChRs was enhanced in the presence of Mg, Na, Co and Ca but strongly inhibited by Hg cations. Cr(VI) uptake capabilities were ranged between 43-97% in R. mucilaginosa and 35-88% in T. asahii. One dimensional electrophoresis revealed enriched bands of cysteine rich metallothioneins suggesting some differential proteins could be overexpressed under Cr(VI) stress.