Associations of Eu (III) with Gram-Negative Bacteria, Alcaligenes faecalis, Shewanella putrefaciens, and Paracoccus denitrificans

We studied the association of Eu (III) with Gram-negative bacteria, Alcaligenes faecalis, Shewanella putrefaciens, and Paracoccus denitrificans by a batch method and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The kinetics study showed that the Eu (III) adsorption on the bacteria rapidly proceeded. The Eu (III) adsorption on A. faecalis and P. denitrificans at pHs 3, 4, and 5, and that on S. putrefaciens at pHs 4 and 5 reached a maximum within 5 minutes after contact. For P. denitrificans, the percent adsorption of Eu (III) decreased after the maximum percent adsorption was attained, which suggests the existence of exudates with an affinity with Eu (III). TRLFS showed that the coordination of Eu (III) on these bacteria is multidentate through an inner-spherical process. The ligand field of Eu (III) on P. denitrificans was as strong as the ones observed for halophilic microorganisms, while that of A. faecalis and S. putrefaciens was the typical one observed for non-halophilic microorganisms. The coordination environment of Eu (III) on the bacteria differed from each other, though they are categorized as Gram-negative bacteria with the similar cell wall components.