Nuclear magnetic resonance studies of biological and biogeochemical processes

Abstract

The research presented uses nuclear magnetic resonance (NMR) experimental techniques to study systems of geochemical and biological processes. This thesis first presents an introduction to the NMR experimental concepts and data analysis. Several experimental systems are then described in detail: biological reduction of uranium; biofilm growth in porous media; and solutions and gels of alginate, a polymer molecule commonly found in the biofilm polymeric matrix. Bioremediation of heavy metal contaminants such as uranium around nuclear waste storage sites is an important environmental problem. Uranyl (UO 2 ²+) is soluble in water, while uraninite (UO 2) precipitates as nanoparticles. Certain types of bacteria are able to use uranium as the electron acceptor and reduce uranyl ions to uraninite. The experiments presented used a solution of uranyl ions that was reduced by a sulfur reducing bacteria and were studied using images and relaxation measurements. The growth of biofilms in the subsurface may also be used for bioremediation. Biofilms form when bacteria attach to surfaces and then produce and live within a polymeric matrix known as the extracellular polymeric substance (EPS). Experiments were done on a biofilm grown through the pore structure of a model bead pack. During the biofilm growth, displacement-relaxation correlation experiments were performed which were able to separate the biofilm phase from the bulk fluid phase using relaxation information. The results presented show that during biofilm growth very little convective flow occurs through the biofilm phase, while pore clogging causes channeling that increases the flow through non-biofilm filled pores and increases hydrodynamic dispersion. The EPS matrix of a biofilm contains DNA, proteins, and biologically produced polymers. Some biofilms such as those produced by the bacteria Pseudomonas aeruginosa contain the polymer alginate. Three biologically produced alginates were compared: alginate produced by algae, alginate produced by P. aeruginosa FRD1153, and alginate produced by P. aeruginosa FRD1. A diffusive reaction gelation process was used to produce heterogeneous gels which were analyzed both during and after gelation. Homogeneous gels and solutions were studied using relaxation dispersion techniques. Differences in hydrogen exchange processes, polymer conformation, and gel structure were analyzed.