The Role of Escherichia coliform in the Biomineralization of Calcium Oxalate Crystals

Abstract

AbstractThe influence of the common bacterium Escherichia coliform (E. coli) on the nucleation and growth of calcium oxalate (CaOxa) in aqueous solution is studied in order to determine its role in the biomineralization of urinary stones. The results show that CaOxa crystals obtained in the presence of E. coli transform more quickly from calcium oxalate dihydrate (COD) into calcium oxalate monohydrate (COM), and they become even larger, than in the absence of the bacterium. On decreasing the concentration of chemical reagents, in other words increasing the ratio bacterium/CaOxa, except for the more rapid phase transition from COD to COM, the CaOxa particles obtained become larger and more regular with a hexagonal morphology. This suggests that E. coli accelerates the crystallization of COM, which is the most stable crystal phase of CaOxa and the major component of urinary stones. Transmission electron microscopy (TEM) images, electron diffraction (ED) patterns, and Fourier‐transform IR (FTIR) spectra show that the biomineralization process of CaOxa crystals takes place both inside and outside the bacterium, which implies that it is induced by both intracellular biomolecules and the bioorganic secretions of the bacteria. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) data and UV/Vis spectra show that the proteins bound to the crystal surface with a molecular weight of around 26.5 kDa have tyrosine, tryptophan, or phenylalanine residues. The zeta potential and FTIR spectra are used to investigate the mineralization mechanism of CaOxa with E. coli and show that, the negatively charged biomolecules inside and outside the bacterium interact with Ca2+ ions to provide nucleation sites and then act as modifiers to induce the nucleation, growth, and aggregation of COM crystals. Therefore, we infer that E. coli mineralizes calcium oxalate and plays a role in the formation of urinary stones.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)