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Physical and chemical effects of extracellular polymers (EPS) on Zn adsorption to Bacillus licheniformis S-86

DOI: 10.1016/j.jcis.2009.05.067 DOI Help
PMID: 19570542 PMID Help

Authors: Janette Tourney (University of Edinburgh) , Bryne Ngwenya (University of Edinburgh) , Marisa Magennis (University of Edinburgh) , Fred Mosselmans (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Colloid And Interface Science , VOL 337 (2) , PAGES 381-3

State: Published (Approved)
Published: September 2009

Abstract: This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl (pK(a) 5.3-5.4) and phosphate (pK(a) 7.4-7.5) functional groups, but with some adsorption to phosphodiester (pK(a) 3.3-3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass. (C) 2009 Elsevier Inc. All rights reserved.

Journal Keywords: Bacteria; EPS; Metal adsorption; Zn; EXAFS

Subject Areas: Chemistry

Instruments: NONE-No attached Diamond beamline