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Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study

Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study
Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study
Bacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ?2–7), with adsorption increasing with pH to a maximum at pH ?6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO5Hn)n?8 monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu–carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1pK basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere triple bond; length of mdashRCOOCu+ surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends log K triple bond; length of mdashRCOOCu+ = 7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio.
0016-7037
6705-6719
Moon, E.M.
e6f7ccfc-7e62-4389-b67f-4f1caadc7b7c
Peacock, C.L.
78fee77e-00ad-421b-8b91-0d331ae9b83b
Moon, E.M.
e6f7ccfc-7e62-4389-b67f-4f1caadc7b7c
Peacock, C.L.
78fee77e-00ad-421b-8b91-0d331ae9b83b

Moon, E.M. and Peacock, C.L. (2011) Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study. Geochimica et Cosmochimica Acta, 75 (21), 6705-6719. (doi:10.1016/j.gca.2011.08.004).

Record type: Article

Abstract

Bacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ?2–7), with adsorption increasing with pH to a maximum at pH ?6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO5Hn)n?8 monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu–carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1pK basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere triple bond; length of mdashRCOOCu+ surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends log K triple bond; length of mdashRCOOCu+ = 7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio.

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Published date: 1 November 2011
Organisations: Ocean and Earth Science

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Local EPrints ID: 202471
URI: https://eprints.soton.ac.uk/id/eprint/202471
ISSN: 0016-7037
PURE UUID: 5e3e3695-5551-472b-9c2a-bc117bb4ddc0

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Date deposited: 07 Nov 2011 14:02
Last modified: 16 Jul 2019 23:19

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Contributors

Author: E.M. Moon
Author: C.L. Peacock

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