Adsorption of rare earth ions onto the cell walls of wild-type and lipoteichoic acid-defective strains of Bacillus subtilis

The aim of this study is to investigate the potential of cell walls of wild-type and lipoteichoic acid-defective strains of Bacillus subtilis 168 to adsorb rare earth ions. Freeze-dried cell powders prepared from both strains were used for the evaluation of adsorption ability for the rare earth ions, namely, La(III), Eu(III), and Tm(III). The rare earth ions were efficiently adsorbed onto powders of both wild-type strain (WT powder) and lipoteichoic acid-defective strain (∆LTA powder) at pH 3. The maximum adsorption capacities for Tm(III) by WT and ∆LTA powders were 43 and 37 mg g −1 , respectively. Removal (in percent) of Tm(III), La(III), and Eu(III) from aqueous solution by WT powder was greater than by ∆LTA powder. These results indicate that rare earth ions are adsorbed to functional groups, such as phosphate and carboxyl groups, of lipoteichoic acid. We observed coagulated ∆LTA powder in the removal of rare earth ions (1–20 mg L −1 ) from aqueous solution. In contrast, sedimentation of WT powder did not occur under the same conditions. This unique feature of ∆LTA powder may be caused by the difference of the distribution between lipoteichoic acid and wall teichoic acid. It appears that ∆LTA powder is useful for removal of rare earth ions by adsorption, because aggregation allows for rapid separation of the adsorbent by filtration.