LiT: Molecular and Electronic Signatures of Pilus Nanowires

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The defining property of all life forms is the generation of energy through electron transfer processes such as respiration, photosynthesis, and elemental cycling, which directly influence our climate and the Earth's resources. As major contributors to our planet's dynamics, bacteria offer a unique opportunity to investigate biological electron transfer. This team has investigated how bacteria termed Geobacter (from the latin "bacteria from Earth") generate energy for growth through the transfer of electrons to insoluble minerals, such as iron oxides. These bacteria produce conductive hair-like filaments (or "pili", from the latin "hair") to establish electronic contact with the minerals. While the conductivity of other biological and physical systems is mediated by associated metals or redox-active organic compounds, the conductive properties of Geobacter pili result from the assembly of a single, small, repeating peptide subunit. Thus, these bacterial "nanowires" have evolved a unique mechanism(s) for efficient electron transport through a protein assembly and serve as a paradigm to study protein-based electron transfer. This project will use a multidisciplinary approach to investigate how Geobacter pili transfer electrons at distances that greatly exceed the reach of the cell. Computational methods will be employed to model the structure and electronic properties of the pili to identify potential pathways for electron transfer. The team will use genetic approaches to engineer pili with predicted defects in electron transfer, which will be assayed in biological and physical assays. Findings from this work will have a significant broader impact via development of groundbreaking scientific knowledge about biological electron transfer and its role in Earth's mineralization processes and climate feedbacks. The proposed work will also provide new fundamental knowledge about multistep electron flow through biomolecular assemblies, which can be harnessed for novel applications in nanobiotechnology, bioenergy, and bioremediation of toxic metals and radionuclides. The proposed work will also be used to train a new cohort of graduate and undergraduate students in interdisciplinary science at the interface of biology, physics, and engineering. A key educational component of this project is the integration of the research in interdepartmental undergraduate courses as well as in a newly developed interdisciplinary graduate program in bioelectronics. Efforts will include (i) curricular development in bioelectronics for graduate students, (ii) a k-12 teacher-training module to increase the national pool of teacher/scholars with the technical knowledge, pedagogical skills, and motivation to effectively teach in this area, and (iii) an aggressive, targeted recruitment effort of students from underrepresented groups by the project's team.