Biosorption of chromium to fungi

Abstract

Eighteen fungal strains were isolated from water and soil samples and tested for their ability to enrich chromium. The microorganism with the highest enrichment capacity, a zygomycete (Mucor hiemalis MP/92/3/4), was chosen for detailed investigations. Some basic tests such as the pH-dependence, the kinetics of the enrichment and the metal selectivity were carried out with the two most frequent oxidation states of chromium, the trivalent cation (Cr3+) and the hexavalent anion (CrO42−). With Cr3+ the enrichment showed a saturation kinetic reaching 70% of the maximum capacity after about 30 min, whereas with CrO42− a linear time course with a much lower metal enrichment was observed. The highest level of enrichment for Cr3+ was observed at pH 5.5 (21.4 mg/g dry wt), and for CrO42− at pH 1 (4.3 mg/g dry wt). Investigations concerning the metal enrichment selectivity resulted in the following series of decreasing ion uptake: Cr3+ > Cu2+ > Pb2+ > Ag+ > Al3+ > Co2+ > Zn2+ > Ni2+ > Fe2+ > Mo5+ > Cd2+ > 2− > CrO42− > VO3−, calculated on a molar basis. Trivalent chromium caused a staining of the outer cell wall region in transmission electron microscopy. The localization of chromium in the stained outer layers of the cell wall could be verified by electron energy loss spectroscopy. The enrichment of Cr3+ by M. hiemalis seemed to be mainly a passive biosorption to the cell wall, whereas for the uptake of CrO42− intracellular accumulation as well as biosorption is possible.