| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 21053 | Journal of Bioscience and Bioengineering | 2011 | 7 Pages |
Ce3+, a rare earth element (REE), has been widely used in high-technology industries. Despite the importance of Ce3+ in the fields of chemistry and physics, the role of Ce3+ in biology has been ignored. To investigate physiological effects of Ce3+ on microorganisms, we screened microorganisms that showed peculiar growth in the presence of Ce3+. We isolated a free-living soil bacterium that produced exopolysaccharide (EPS) around its colonies on 1/100 nutrient agar with 30 μM CeCl3 or 1.0% d-mannitol. The bacterium was identified as Bradyrhizobium sp. by morphological, biochemical, and physiological tests as well as 16S rDNA sequence analysis. La3+, Pr3+, and Nd3+ also induced EPS production in large quantities, while Sm3+ did in small amounts. However, other heavier REEs from Eu3+ to Lu3+, and metals such as Na+, Al3+, K+, Ca2+, V3+, Cr3+, Co2+, Ni2+, Sr2+, Ba2+, and Pb2+ did not induce EPS production. The mean molecular weight of EPS was estimated to be approximately 1 × 106 by Sepharose CL-4B column chromatography. TLC revealed that EPS was composed of l-rhamnose. Quantitative analysis of alditol acetate derivatives of acid hydrolyzate of EPS by GLC revealed that EPS was composed of more than 95% l-rhamnose, indicating that this EPS was a rhamnan. The spectrum of FT-IR of the rhamnan demonstrated that l-rhamnose residues in the rhamnan were α-linked. GC/MS analysis of methylated alditol acetate derivatives of the rhamnan demonstrated that it was composed of main chain α-(1→4)-linked l-rhamnopyranosyl residues. From spectral analyses of 1H-NMR and FT-IR, EPS produced in the presence of 1.0% d-mannitol was found to be structurally similar to rhamnans.
