Bioremediation of Cr(VI) by yeasts: the importance of inoculum standardization.

FERNÁNDEZ PM; FIGUEROA LIC; SIÑERIZ F; FARIÑA JI

Denver, CO, USA.

Congreso; Annual Meeting and Exhibition 2007 of the Society for Industrial Microbiology (SIM); 2007

Society for Industrial Microbiology

Physical and chemical methods for cleanup of Cr(VI) are not cost-effective and not recommended for small-scale remediation processes. However, Cr(VI) detoxification using chromium resistant microorganisms has been considered economical, effective and a safe procedure. Two chromate-resistant yeasts isolated from textile factory wastewaters were identified as Candida anomala and Pichia jadinii. Cr(VI) removal assays were performed in YNB (w/o AA and ammonium sulfate) medium supplemented with sucrose as C-source and ammonium sulfate as N-source, plus 1mM Cr(VI) as K2Cr2O7. Shake culture flasks were incubated at 25ºC, 250 rpm, during 4 days. After 48 h of cultivation, Cr(VI) was completely reduced and undetectable in culture supernatants. At the same time, there was an increase in extracellular Cr(III) content, as detected by a colorimetric method with Chromazurol S. That helped us to confirm that the mechanism of Cr(VI) remediation involved reduction to Cr(III). Cr(VI) removal performance was substantially affected by the inoculation procedure. It was highly significant for a given yeast strain when cultures were inoculated with high biomass density and pre-grown in a nutritionally rich culture medium (like Czapek malt). On the other hand, the use of poor and/or synthetic media such as YNB led to lower biomass concentration, and the obtained inoculum was unsuccessful for Cr(VI) removal. Results revealed the potential of the selected yeasts for Cr(VI) removal by biospeciation. However, these results emphasize the importance of selecting a given culture medium and an appropriate inoculum cell density in order to achieve a successful Cr(VI) bioremediation.