Comparison of the acid-base behaviour and metal adsorption characteristics of a gram-negative bacterium with other strains |
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| Institution: | 1. Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK;2. Institute of Cell and Molecular Biology, University of Edinburgh, Daniel Rutherford Building, Mayfield Road, Edinburgh EH9 3JH, UK;1. George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States;2. Tucker Innovations, Inc, Charlotte, NC, United States;1. British Geological Survey, Edinburgh, EH14 4AP, UK;2. School of GeoSciences, University of Edinburgh, EH9 3FE, UK;1. Biomaterials Unit, University of Birmingham School of Dentistry, College of Medical and Dental Sciences, St Chad''s Queensway, Birmingham B4 6NN, UK;2. Materials Science Unit, Division of Oral Biosciences, Dublin Dental University Hospital, Trinity College Dublin, Lincoln Place, Dublin 2, Ireland;1. National Centre for Seismology, Ministry of Earth Sciences, Mausam Bhawan Complex, New Delhi 110003, India;2. Former Addl. D. G., India Meteorological Department, New Delhi 110003, India;1. Departamento de Tecnologia Rural e Animal, Universidade Estadual do Sudoeste da Bahia, Praça Primavera, 40, Bairro Primavera, 45700-000, Itapetinga, BA, Brasil;2. Departamento de Tecnologia de Alimentos, Universidade Federal de Viçosa, Campus Universitário, s/n, Centro, 36570-000, Viçosa, MG, Brasil;3. IBB–Institute for Biotechnology and Bioengineering, Centre for Biological Engineering, Universidade do Minho, Campus de Gualtar, 4710-057, Braga, Portugal;4. Centro de Química, Universidade do Minho, Campus de Gualtar, 4710-057, Braga, Portugal;5. Department of Agricultural, Food and Nutritional Science (AFNS), University of Alberta, T6G 2P5, Edmonton, AB, Canada |
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| Abstract: | Thermodynamic parameters for proton and metal adsorption onto a gram-negative bacterium from the genus Enterobacteriaceae have been determined and compared with parameters for other strains of bacteria. Potentiometric titrations were used to determine the different types of sites present on bacterial cell walls. Stability constants for adsorption of Pb, Cu and Zn to specific sites were determined from batch adsorption experiments at varying pH with constant metal concentration. Titrations revealed 3 distinct acidic surface sites on the bacterial surface, with pK values of 4.3±0.2, 6.9±0.5 and 8.9±0.5, corresponding to carboxyl, phosphate and hydroxyl/amine groups, with surface densities of 5.0±0.7×10?4, 2.2±0.6×10?4 and 5.5±2.2×10?4 mol/g of dry bacteria. Only carboxyl and phosphate sites are involved in metal uptake, yielding the following intrinsic stability constants: Log Kcarboxyl: Zn=3.3±0.1, Pb=3.9±0.8, and Cu=4.4±0.2, Log Kphosphoryl: Zn=5.1±0.1 and Pb=5.0±0.9. The deprotonation constants are similar to those of other strains of bacteria, while site densities are also within an order of magnitude of other strains. The similarities in surface chemistry and metal stability constants suggest that bacteria may be represented by a simple generic thermodynamic model for the purposes of modelling metal transport in natural environments. Comparison with oxide-coated sand shows that bacteria can attenuate some metals to much lower pH values. |
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