Abstract's Details

Zn²⁺ and Pb²⁺ Adsorption on to Shewanella oneidensis:Determination of Surface Complex Structure Using Spectroscopic and Modeling Approaches
Abstract ID	ENV-07
Presenter	Juyoung Ha
Presentation Type	Poster
Full Author List	J. Ha (1), A. Gelabert (1), Y. Wang (1), A. Spormann (2), G. Brown, Jr. (1,3)
Affiliations	(1) Surface & Aqueous Geochemistry Group, Dept. of Geological & Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA (2) Dept. of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305 USA (3) Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, SLAC, MS 69, Menlo Park, CA 94025, USA
Category	Environmental Science
Abstract	The role bacteria as a metal adsorbant and/or as a template for nucleation and growth of metal precipitation is significant in predicting the overall fate and transport of metals due to strong attraction of bacterial surface to soluble metals and the abundance of microorganisms in many geological systems. Hence, developing models that can quantify bacteria-metal adsorption are critical for predicting the mobility of metals. In this study the Shewanella oneidensis strain MR-1 (wild type) and exopolysaccharide deficient mutant strain (dleta_EPS) of S. oneidensis were examined to describe thermodynamic and chemical properties of the bacterial surfaces. Adsorption affinity of the bacteria for several different metal cations (e.g., Pb²⁺ and Zn²⁺) were also tested and modeled within the framework of a constant capacitance model using FITEQL computer code. ATR-FTIR spectra of both strains exhibited carboxyl, amide and phosphate groups, as well as carbohydrate molecules. Loss of exopolyssacharides from the cell surface was observed by the disappearance of the polysaccharide peak around 1100 cm-1 for ∆EPS mutant cells, while potentiometric titration of both strains of bacteria indicated that they exhibit similar surface charge as a function of pH. This suggests, in agreement with our preliminary modeling results, a weak contribution of the removed polysaccharides to the overall charge of S. oneidensis surfaces. No significant differences were observed between the different ionic strengths investigated (1M, 0.1M, and 0.01M of NaNO3), indicating that the physical structure of the cell wall does not depend on the electrolyte concentration. Negative electrophoretic mobilities at pH > 3.5 were observed for S. oneidensis wild type indicating that the outermost layer of organic groups bear negative charges. Based on these experimental results, thermodynamic stability of metal complexes on the two different strains of S. oneidensis and concentration of binding sites on the bacterial surfaces for such complexes will be quantitatively determined.
Footnotes	1. Yee et al. (2004) Geochim. Cosmochim. Acta 68(18), 3657-3664 2. Yee, N. and Fein, J. B. (2002) Chem. Geol. 185(3-4), 303-319 3. Myers, R. and Myers, M. (2003) Lett. Appl. Microbiol. 37(3), 254-258 4. Ngweny et al. (2003) Appl. Geochem. 18, 527 - 538 5. Thormann et al. (2006) J. Bacteriol. 188(7) 2681 - 2691 6. Gelabert et al. (2004) Geochim. Cosmochim. Acta 68(20) 4039 - 4058 7. Naneem et al. (2006) Environ. Sci. Technol. 40(18) 5724 - 5729 8. Fein et al. (2005) Geochim. Cosmochim. Acta 69(5) 1123 - 1132.
Funding Acknowledgement	Funding for this work is from NSF-EMSI Grant CHE-0431425 and an NSF-NIRT Grant BES-0404400. We would like to thank beamline scientists John Bargar and Joe Rogers (SSRL) for their assistance during beam time and Guangchao Li for help with ICP analysis.