Evolution of the response to fluctuating oxygen availability in facultative anaerobes

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This project will lead to a better understanding of how microbes respond to changes in oxygen availability. Some organisms can only tolerate very small fluctuations in oxygen availability. Others, including many bacteria and fungi are able to live with or without oxygen, and at all oxygen concentrations in between. These organisms accomplish this flexibility by shifting how they generate energy from an oxygen-dependent process called aerobic respiration to oxygen-independent processes like fermentation. This flexibility allows these organisms to live in a wide variety of different environments, but it comes at a cost. The overall goal of this project is to better understand the molecular and genetic basis of that cost. To date, this has been investigated in a very small number of organisms, leaving a major gap in our understanding of why some organisms are better equipped than others to adjust to fluctuating oxygen availability in natural environments. This project will fill that gap by comparing the molecular response of a much larger number of bacteria. Results from this project will have implications for understanding how oxygen availability impacts interaction of bacteria with plant and animal hosts. Project results will also have implications for biotechnology applications, like biofuel generation and other engineered bioprocesses which depend on manipulation of oxygen availability in industrial settings. Finally, this project will provide training and educational opportunities at the university, outreach activities to increase science literacy for K-12 students, and professional development opportunities for high school and middle school teachers.This project will focus on the evolutionary impact of fluctuating oxygen availability on facultative-anaerobic bacteria. The project builds on preliminary growth rate and transcriptome data from a small number of strains of enterobacteria. Aim 1 will measure fitness impacts of standing variation in natural populations under rigorously controlled oxygen availability conditions using large-scale phenotyping. Aim 2 will link genetic and phenotypic variation using association studies with both genome sequences and transcriptomes, and population genetic tests for genome-wide footprints of balancing selection. A subset of implicated loci will be validated using genome engineering. Aim 3 will test whether regular fluctuations in oxygen availability in experimentally evolved populations leads to persistence of conditionally advantageous and/or antagonistically deleterious variation. Results from this project are expected to significantly advance understanding of the significance of natural variation in the response to oxygen availability and the molecular underpinnings of fitness tradeoffs in heterogeneous environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.