Collaborative Research: Unraveling the bacterium-mineral interface - Nanoscale structures and forces

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EAR-0525297, Lower, Ohio State University Research FoundationEAR-0525340, Bickmore, Brigham Young UniversityEAR-0525151, Beveridge, University of Guelph Bacteria are the most prolific group of organisms on the Earth in terms of their geographic extent as well as their longevity across geologic time. Most bacteria live by creating habitats on the surface of solid particles such as minerals, which may be located in soil, subsurface, or aquatic environments. Bacteria perceive the presence of mineral surfaces through force "cues", which allow a cell to physically feel another surface. While inter- and intra-molecular forces dominate the lives of microorganisms, their seemingly infinitesimal magnitude and length-scale have made them difficult to study. This proposed research will begin to shed light onto this problem though a unique combination of molecular modeling, force measurements, and microscopic images of well-characterized silica minerals and bacteria that have been genetically modified to produce specific cell wall macromolecules. First, the natural distribution, density, and acid-base reactivity of functional groups on specific faces of phyllosilicate and silicate crystals (and possibly also on the surface of a bacterium) will be determined with atomic force titration measurements. These measurements will be interpreted with a new method for predicting acid-base reactivity of individual functional groups that involves ab initio structure calculations. Second, atomic force microscopy will be used to measure intermolecular forces between wild-type and mutant strains of Pseudomonas aeruginosa and silicate minerals. These force measurements will be interpreted in light of the previously obtained molecular-scale models of the mineral surface acid-base reactivities. The intellectual merit of this proposal is that the combination of molecular models with force measurements will allow an unprecedented view of the fundamental forces or cues that exist at the interface between a living bacterium and mineral surface in situ. This goal will be accomplished through the collective efforts of our interdisciplinary research team that includes scientists specializing in geochemistry, mineralogy and molecular modeling (Bickmore and Lewis), geomicrobiology and nanoscience (Lower and Beveridge), and physical force laws (Dutcher and Israelachvili). The microorganism used in these experiments, P. aeruginosa, is a model Gram negative bacterium. It is ubiquitous in water, soil, and subsurface environments where it lives on the surface of minerals or other particles. It is also a common bacteria species on plants and animals, where it often functions as an opportunistic pathogen. The minerals used in these experiments include silicates, which are the most common inorganic phases on Earth. Probing the interface between P. aeruginosa and silicate minerals will have broader implications and societal benefits that can be applied to issues ranging from the transport of microorganisms in aquifers to the formation of biofilms on solid substrates. Further, this proposal will impact the lives of a number of graduate students and undergraduates. These students will be cross trained in biochemistry, microbiology, geochemistry, and mineralogy, and they will also gain experience with state-of-the-art instruments such as scanning probe microscopes, laser scanning microscopy, and transmission electron microscopy. Finally, this proposal will provide funds to support K-6 outreach programs that are designed to expose young students to the interplay between the biological and physical sciences.