Corynebacterium glutamicum-mediated crystallization of silver ions through sorption and reduction processes

The processes of biosorption and bioreduction can provide important insights for understanding the mechanisms underlying the biosynthesis of nanoparticles. We performed various experiments using active/live and inactive/dead cells of Corynebacterium glutamicum to determine the capacity of these cells to adsorb and/or reduce silver ions. The biosorption of silver increased with increases in pH and equilibrium achieved within 30 min. The maximum experimental uptake with an initial silver concentration of 1000 mg/L was found to be 50.1 mg/g for active cells and 52.5 mg/g for inactive cells. After biosorption, we investigated the bioreduction capacity of both active and inactive cells of C. glutamicum. Strong plasmon resonance of silver nanoparticles was observed between 400 and 450 nm in the samples obtained from both active and inactive C. glutamicum. Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were performed to examine the formation of silver nanoparticles. A significant difference was noted in the formation of nanoparticles by live and inactive cells. A larger amount of reduction occurred on the surfaces of inactive cells. The nanoparticles formed were very irregular in shape and ranged in size from 5 to 50 nm. In the present study, the possibility of nanoparticles formation even in the absence of enzymes and metabolites has been studied. Crystallization of silver ions from aqueous solution by both active and inactive biomass can form a possible platform for a cost effective and eco friendly technique to remove or recover noble metals.