Tolerance to silver of an Aspergillus fumigatus strain able to grow on cyanide containing wastes

Abstract

We studied the strategy of an Aspergillus fumigatus strain able to grow on metal cyanide wastes to cope with silver. The tolerance test revealed that the Minimum Inhibitory Concentration of Ag(I) was 6mM. In 1mM AgNO3 aqueous solution the fungus was able to reduce and sequestrate silver into the cell in the form of nanoparticles as evidenced by the change in color of the biomass and Electron Microscopy observations. Extracellular silver nanoparticle production also occurred in the filtrate solution after previous incubation of the fungus in sterile, double-distilled water for 72h, therefore evidencing that culture conditions may influence nanoparticle formation. The nanoparticles were characterized by UV-vis spectrometry, X-ray diffraction and Energy Dispersion X-ray analysis. Atomic absorption spectrometry revealed that the optimum culture conditions for silver absorption were at pH 8.5.The research is part of a polyphasic study concerning the behavior of the fungal strain in presence of metal cyanides; the results provide better understanding for further research targeted at a rationale use of the microorganism in bioremediation plans, also in view of possible metal recovery. Studies will be performed to verify if the fungus maintains its ability to produce nanoparticles using KAg(CN)2.

Keywords: Metal cyanide waste; Nanoparticle production; Silver tolerance.