Cr(VI) Reduction in Highly Chromate-Resistant Yeast Isolated from Textile-Dye Polluted Enviroments

PM FERNANDEZ; SC VIÑARTA; LIC FIGUEROA; JI FARIÑA

Orlando, Florida., USA

Congreso; 106th General Meeting of the American Society for Microbiology (ASM); 2006

American Society for Microbiology

Background. Yeast and fungi are a very diverse group of eukaryotic microorganisms potentially able for bioremediation of chromium and other heavy metals. They may exhibit bioaccumulation or biospeciation to non-toxic and bioavailable Cr forms. By sampling in a site receiving textile factory effluents (Maravilla Stream, Tucum¨¢n, Argentina), potentially exposed to metal pollution, we aimed the isolation of Cr-tolerant fungal species. Methods. Polluted-site samples were used for 100 mL-microcosms with YNB medium plus 1mM Cr(VI) as K2Cr2O7 with sucrose and (NH4)2SO4. They were incubated at 250 rpm and 25¡ãC with 5.2-mg Cr(VI) pulses at 36 and 72 h. After plating on YNB, isolates with different morphotype were selected for semi-quantitative analysis (1-50 mM Cr(VI)-YNB). Highly Cr(VI)-tolerant isolates were evaluated in liquid medium plus 1mM Cr(VI). Dry weight biomass and residual Cr(VI) (DPC method) were estimated. Chromate reductase activity was assayed in culture supernatants as well as in sonicated fractions. Enzyme reaction mixtures contained 0.5 mM Cr(VI) as K2CrO4 and 1 mM NADH and 200 ¦Ìl enzyme (pH 5). After incubation at 30¡ãC, remaining Cr(VI) was determined as above. Cell oxidative stress was evaluated in the presence of 1.5 mg/mL ABTS. Results. Microcosms enrichments led to 49 fungal isolates and they were subjected to semi-quantitative analysis. The majority of the 18 selected isolates were able to tolerate up to 50 mM Cr(VI). Twelve isolates were selected based on their high Cr(VI) removal efficiencies (65-95% after 24-h) after liquid culture with 1 mM Cr(VI). High and similar activities (500-600 nmol Cr(VI)/min) were detected both for sonication pellets (12,000 g/15 min) and sonication supernatants for the 12 selected isolates. None of isolates revealed formation of ROS, demonstrating cells under oxidative stress. Conclusions. Results revealed the potential of the selected yeasts for Cr(VI) bioremediation. The implicated mechanism seems to be biospeciation through chromate-reductase activity that may be cell-wall located and/or in the cytoplasmic fraction.