Fungal bioremediation of chromates: conformational changes of biomass during sequestration, binding, and reduction of hexavalent chromium ions.

This paper highlights the mechanistic aspects of white rot fungus Coriolus versicolor as a complexing/reducing agent for chromium bioremediation. The chemical reduction of Cr(VI) to Cr(III) via the formation of Cr(VI) thio ester as an intermediate, is pH dependent and controls the overall chromium adsorption kinetics. The strong adsorption affinity of the biomass towards Cr(VI) anions was evaluated by the Freundlich and the Langmuir adsorption isotherms. The FTIR spectroscopic analysis suggested the involvement of amino, carboxylate, and thiol groups from fungal cell wall in chromium binding and reduction. The mechanism of the adsorption was preferential sequestration along with binding of the metal to the ligating groups present in the biomass followed by reduction to trivalent state. The results indicate step-wise progression of overall reaction dictated and modulated by structural and conformation effects in the biomass that lead to saturation, acceleration, and ultimate saturation kinetics effects.