Perspective in bioremediation: enhancing the hexavalent chromium removal using native yeasts from Tucumán, Argentina

Abstract

The occurrence of indigenous Cr(VI)-reducing eukaryotic microorganisms, including those with no history of Cr(VI) contamination, has provided important non conventional yeasts with significant biological relevance and biotechnological applications. Based on physiological/biochemical characterization and molecular taxonomy analysis, these isolates were identified as Cyberlindnera jadinii M9 and Wickerhamomyces anomalus M10. Cy. jadinii M9 and W. anomalus M10 were grown in medium plus 1 mM Cr(VI) at 25°C, causing complete chromium removal before reaching 48 h of cultivation. Flame Atomic Absorption Spectroscopy (FAAS) assays suggested that Cr(VI) disappearance was coupled to the Cr(III) concomitant production. These results indicated that reducing capacity of chromate-resistant yeasts would be the main detoxification mechanism. Crude chromate reductase (CChRs) of strains M9 and M10, were characterized based on optimal temperature, pH, use of electron donors, metal ions and initial Cr(VI) concentration in the reaction mixture. Both CChRs showed an increase in Cr(VI) reductase activity with addition of NAD(P)H as electron donor and were highly inhibited by Hg2+ and Mn2+ 32 . The CChR from Cy. jadinii M9 showed the highest chromate reductase activity at 60 ºC and pH 6.0 in the presence of Cu2+ or Na+, while W. anomalus M10 CChR had the maximum activity at 50 ºC and pH 7.0 in presence of Cu2+ 35 . Initial Cr(VI) concentrations of 1.3 and 1.7 mM for CChRs of Cy. jadinii M9 and W. anomalus M10 respectively were inhibitory. This chapter presents evidence of the significant potential of native selected yeasts for chromium bioremediation, thus being promising candidates for alleviating this polluting metal from environment.