Study of macromolecule-mineral interactions on nuclear related materials

Microbes have been identified close to contaminated sites such as nuclear-waste repositories indicating their ability to interact with radionuclides. One of the main mechanisms bacteria use involves the reduction of highly mobile radionuclides to less mobile minerals, often in the form of oxides. The precipitated minerals are found located at the cell wall or close to the external components of the bacterial cell suggesting a possible interaction of cell wall components or external components of the tested bacteria with the precipitated particles. Tests on ceria, urania, thoria and europium oxide confirmed that several biomolecules are responsible for the observed localisation. The first experiments used lipopolysaccharides (LPS), found at the outer site of Gram negative bacterial cells and resulted in successful sorption of LPS on all four minerals. The Purpald assay was used to quantify LPS before and after the interaction and confirmed the attachment of the biopolymers to the oxides with ΔG values in the range of physisorption (-3 to -25 kJ/mol) for all systems. ATR-FTIR, zeta potential analysis and electron microscopy also confirmed the attachment of the biomolecules on the minerals. Mycolic acids and peptidoglycans, components of Gram positive bacteria, were also assessed for their ability to interact with ceria and europium oxide. Mycolic acids showed successful sorption profiles with ΔG values in the physisorption range (-10 to -17 kJ/mol) for all systems, highly dependent on the experimental conditions. In addition, Molecular Dynamics simulations were used to examine the interaction of mycolic acid with ceria under natural conditions (pH7) in the presence of Na+ and the calculated binding energy (-11.598 kJ/mol) agreed well with the experimental results for the corresponding system (-16.485 kJ/mol). Additionally, preliminary tests on peptidoglycan interactions resulted in successful sorption of the biomolecule on both ceria and europium oxide with ΔG values in the physisorption range (-8 to -10 kJ/mol). ATR-FTIR and zeta potential analysis confirmed the attachment of mycolic acid and peptidoglycan on the minerals tested. These results suggest that the observed localisation of mineral within the bacterial cell walls are related to lipopolysaccharide and peptidoglycan-mediated sorption and have potential uses in treatment of nuclear waste and biomining processes.