Characterization of Cr(VI) removal from arqueous solutions co-contaminated with Cu(II) using an indigenous yeast

Abstract

Chromium(VI) compounds are known to be extremely toxic to livingorganisms due to their strong oxidizing nature. Biological Cr removal offers analternative to traditional physic-chemical methods and is considered as asustainable technology of lower impact on the environment. Resistantmicroorganisms have been studied they may exhibit Cr-bioaccumulation orbiospeciation mechanisms. The endophytic Rhodotorula mucilaginosa 7Apo1 from sugar cane was testedon their Cr(VI) removal and resistant mechanism when it was incubated in YMmedium plus different concentrations of Cr(VI) and Cr(VI)+Cu(II). ResidualCr(VI) (1,5-Diphenylcarbazide method) and total Cr (Atomic AbsoprtionSpectroscopy) were estimated. Cell observations were made by scanning electronmicroscopy SEM and by EDS dispersive energy spectroscopy.7Apo1 was able to remove 100% of the 0.5 mM Cr(VI)initial concentration after 96 h of cultivation, whereas with 0.25mM Cu(II) + 0.5mM Cr(VI) the removal was reached at 48 h.Similar behavior was observed at higher concentrations [1 mM Cr(VI) and 0.25 mMCu(II) + 1mM Cr(VI)], but not reaching the total Cr(VI) removal.Most of the total chromium was detected in the cell-free supernatants (whichmight be ascribed to the trivalent state) with a minimal residual proportion inthe biomass digested with acid. The analysis by SEM showed changes in thegeneral appearance and shape of cells according to the control cultures whilstEDS analysis of 7Apo1 exposed to Cr showed spectra with almost imperceptiblelow levels of the metal on the cell surface. The results herein presented put in evidence that the capability of theyeast 7Apo1 for Cr(VI) removal are highly influenced by the presence of lowconcentrations of Cu(II). Accordingly, bioreduction may be suggested as themain mechanism implicated in the removal of Cr(VI) from cultures. Furthermore, lowbioaccumulation is not located on the cell surface.