A further insight into the mechanism of Ag+ biosorption by Lactobacillus sp. strain A09

The mechanism of Ag+ biosorption by resting cell of Lactobacillus sp. strain A09 has been further investigated at the molecular level using spectroscopic techniques. The values of estimated equilibrium constants, rate constants, half-life periods and apparent enthalpies of the binding reaction were calculated via the determination of Ag+ adsorbed by the biomass using atomic absorption spectrophotometry (AAS). The reductive ratio of the Ag+ to Ag0 by the A09 biomass was examined by X-ray photoelectron spectroscopy (XPS). Analysis for sulfur and nitrogen atomic contents in dry powder of the biomass with EA-1110 elemental analysis (EA) showed that amino acid residues retaining the reductive property of Ag+ to Ag0 are very small quantity, whereas glucose content in the hydrolysates of the biomass analyzed by ultraviolet-visible spectrophotometry (UV-vis) indicated that the amount of reducing sugars in the biomass is much larger than 2.71%. The fourier transform infrared (FTIR) spectrophotometry on blank and silver-loaded biomass demonstrated that the chemical functional group such as the free aldehyde group of the hemiacetalic hydroxyl group from reducing sugars, i.e. the hydrolysates of the polysaccharides from the cell wall plays a leading role in serving as the electron donor for reducing the Ag+ to Ag0. This result was further supported by characterizations on the interaction of the Ag+ with glucose using X-ray powder diffractometry (XRD) and FTIR spectroscopy.