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

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

INTERNATIONAL BIODETERIORATION & BIODEGRADATION

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2013 vol. 79 p. 28 - 35

0964-8305

Chromate-resistant microorganisms able to reduce toxic Cr(VI) into insoluble Cr(III) are seen as promising candidates for alleviating Cr(VI)-contamination. In this study, chromate-reducing yeasts could be 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 reveal a progressive tolerance increase to Cr(VI). However, fungal colony numbers decreased after 108 h of cultivation most likely as a consequence of the accumulated toxic effects of metal during enrichment. From 49 different Cr(VI)-tolerant fungal morphotypes isolated under selective conditions, 12 yeasts showed resistance up to 50 mM and 6filamentous fungi up to 2 mM. These highly tolerant yeasts could be subsequently grouped into 8 OTUs(Operational Taxonomic Units) according to the ITS1-NL4 RFLP (Restriction Fragment Length Polymorphism) analysis. From them, microsatellite amplification, sequencing and Cr(VI)-removal ability allowed to select two representative isolates. A polyphasic approach including morphological, physiological/biochemical characterization and molecular taxonomy analysis allowed to identify these isolates as Cyberlindnera jadiniiM9 (previouslyPichia jadinii) and Wickerhamomyces anomalusM10 (previously Pichia anomala).Cy. jadiniiM9 andW. anomalusM10 were grown in YNB? medium plus 1 mM Cr(VI) at 25C and pH 5.0, causing complete chromium removal before reaching 48 h of cultivation. Flame Atomic Absorption Spectroscopy (FAAS) assays suggested that Cr(VI) withdrawal was coupled to Cr(III) appearance. Electron microscopy studies indicated absence of precipitates on the cell wall region or microprecipitates into the cellular cytoplasm. These complementary results revealed that biospeciation to Cr(III) would the main detoxification mechanism in selected chromate-resistant yeasts, which could be thus envisaged as promising tools for future biological treatment of Cr(VI) pollution