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Title: The role of bacterial extracellular polymers in cell surface chemistry, metal adsorption and biomineralisation
Author: Tourney, Janette
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2008
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This study aimed to characterise the role of bacterial extracellular polymers in surface reactivity, metal adsorption and biomineralisation. This was undertaken using an EPS-producing, thermophilic, bacterial strain, Bacillus licheniformis S-86. Experimental work was undertaken comparing cells with the EPS layer intact (native cells) with cells from which the EPS layer had been extracted (EPS-free cells). The study incorporated surface characterisation by potentiometric titration, infrared analysis and electrophoretic mobility analysis. Investigation of the mechanisms of zinc and nickel adsorption to cell surfaces was undertaken by both macroscopic batch adsorption experiments, and spectroscopic (EXAFS) analysis. Surface complexation modelling of the potentiometric titration data indicated that the native and EPS-free cells contained four proton-active functional groups, with pKa values of 3.3-3.4, 5.3-5.4, 7.4-7.5 and 9.9-10.1. These were tentatively identified as phosphodiester, carboxyl, phosphoryl and hydroxyl/amine groups respectively, and ATR-FTIR analysis supported identification of the pKa 5.3-5.4 site as carboxylic. The site concentrations of the pK3.3-3.4 and 9.9-10.1 groups were significantly lower in the EPS-free cells than in the native cells. Both the macroscopic and EXAFS metal adsorption studies indicated that the carboxyl group is of principle importance to Zn complexation, and a lack of temperature-dependent adsorption provides evidence that Zn binds by an outer-sphere mechanism. Results for Ni did not provide a conclusive explanation of the binding mechanism. Biomineralisation experiments indicated that the presence of EPS affects both CaCO3 morphology and polymorphism. The metastable polymorph vaterite appears less stable in the presence of EPS. The results of this study have shown that EPS, and potentially the associated dissolved organic carbon, can significantly affect the surface reactivity of bacterial cells.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available