Do Exudates Affect Cadmium Speciation and Bioavailability to the Rhizobacterium Sinorhizobium meliloti?

Karine Dedieu; Tatiana Iuranova; Vera I. Slaveykova

doi:10.1071/EN06063

RESEARCH FRONT

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Do Exudates Affect Cadmium Speciation and Bioavailability to the Rhizobacterium Sinorhizobium meliloti?

Karine Dedieu ^A , Tatiana Iuranova ^A and Vera I. Slaveykova ^A ^B

+ Author Affiliations

- Author Affiliations

^A Environmental Biophysical Chemistry, ISTE-ENAC, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 2, CH 1015 Lausanne, Switzerland.

^B Corresponding author. Email: vera.slaveykova@epfl.ch

Environmental Chemistry 3(6) 424-427 https://doi.org/10.1071/EN06063
Submitted: 23 October 2006 Accepted: 29 November 2006 Published: 13 December 2006

Environmental Context. Heavy metals such as cadmium can affect soil microbes and consequently perturb important nutrient cycles resulting in deterioration of the soil fertility. Conversely, soil bacteria might influence cadmium cycling, bioavailability and ecotoxicity by producing exudates such as proteins, polysaccharides and siderophores. These substances are shown to form complexes with cadmium, decreasing the free concentration of cadmium in soil solutions.

Abstract. To better understand the role of exudates in cadmium (Cd) speciation and biouptake by the bacterium Sinorhizobium meliloti, the content of various exudate components, including siderophores, proteins and polysaccharides, was quantified in the absence and presence of 10 μM Cd at pH 5.0 and pH 7.0. The obtained results demonstrate that the release of exudates by S. meliloti is a constitutive process rather than one induced by the presence of Cd. Nonetheless, exudates complex Cd and significantly reduce its free ion concentration. Cd bioavailability to S. meliloti was characterized by the amount of adsorbed and intracellular Cd. Adsorbed Cd at pH 5.0 was higher than that at pH 7.0, which is consistent with the higher free Cd concentration and lower amounts of exudates released at that pH. The observed reduction in intracellular Cd at pH 5.0 compared with pH 7.0 was attributed to the prevailing competition between protons and Cd ions for transport sites.

Keywords. : bacteria — bioavailability — bound residues — exudates — soil chemistry

Acknowledgements

Swiss National Science Foundation PP002–102640 is acknowledged for providing funding directly related to this work. Discussions with A. Kraepiel-Morel about siderophore release were extremely helpful, as were critical reviews of a previous draft of the manuscript by C. Lamelas and R. Hajdu. We thank two anonymous reviewers for their constructive comments, which helped us to improve the manuscript.

References

Do Exudates Affect Cadmium Speciation and Bioavailability to the Rhizobacterium Sinorhizobium meliloti?

Acknowledgements

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