The biosorptive interaction of Ag+ with resting cell of Lactobacillus sp. strain A09 has been further studied on a molecular level by means of XPS, EDX, UV-Vis and FTIR techniques. The X-ray photoelectron spectroscopy (XPS) shows that the reductive ratio of the Ag+ to Ag-0 by the A09 biomass reaches to about 54.5% for 3 d. The contain of amino acid residues in dry powder of the biomass such as cysteine, methionine, arginine and lysine, being capable of reducing the Ag+ to Ag-0 are very small in quantity both cysteine and methionine are far less than 0.18%, and both arginine and lysine far less than 0.336%,via the analysis with quantitative energy-dispersive X-ray (EDX). The amount of the reducing sugars in the biomass is far larger than 2.71% analyzed by ultraviolet-visible spectrophotometry (UV-Vis). The chemical functional group on cell wass of the biomass such as the carboxylate anion of amino-acid residues seems to be the site for the Ag+ binding and the free aldehyde group of the hemiacetalic hydroxyl from reducing sugars, i.e. the hydrolysates of the polysaccharides from the cell wass, plays a protagonist in serving as the electron donor for reducing the Ag+ to Ag-0, characterized by fourier transform infrared (FTIR) spectrophotometry
