Textile-dye polluted waters as an unusual source for selecting chromate-reducing yeasts through Cr(VI)-enriched microcosms

FERNÁNDEZ, PABLO M; CABRAL , ME; DELGADO, OSVALDO D.; FARIÑA, JULIA I; FIGUEROA, LUCÍA I. C.

INTERNATIONAL BIODETERIORATION & BIODEGRADATION

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2012

0964-8305

Chromate-resistant microorganisms with the ability of reducing toxic chromate, Cr(VI), into insoluble trivalent chromium, Cr(III), are promising candidates for alleviating Cr(VI)-contamination. In this study, chromate-reducing yeasts were isolated from a textile-dye effluent and associated biofilm by using microcosm methodology with periodical 1 mM Cr(VI)-pulses. Viable cell count seemed to indicate an adaptation process to the metal presence. However, after 108 h, fungal colony numbers decreased as a consequence of the toxic effects of accumulated metal during the enrichment process. Selective conditions led to 49 different Cr(VI)-tolerant fungal morphotypes, from which 12 yeasts showed resistance up to 50 mM, and 6 filamentous fungi up to 2 mM. These highly tolerant yeasts were subsequently grouped into 8 OTUs according to the ITS1-NL4 RFLP analysis and then, microsatellite amplification led to two representative isolates. Based on morphological, physiological/biochemical characterization and molecular taxonomy analysis, these isolates were identified as Cyberlindnera jadinii M9 (previously Pichia jadinii) and Wickerhamomyces anomalus M10 (previously Pichia anomala). C. jadinii M9 and W. anomalus M10 were grown in YNB´ medium plus 1 mM Cr(VI) at 25°C and initial pH 5.0, 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. Electron microscopy studies indicated absence of precipitates on the cell wall region or microprecipitates into the cellular cytoplasm. These results indicated that reducing capacity of chromate-resistant yeasts would be the main detoxification mechanism and they could be used as tools for future treatment of Cr(VI) pollution.