From the lab of Kathryn Fixen…
Solar energy has enormous potential as a source of alternative energy. The amount of solar energy that hits the earth every day is 20,000 times greater than the amount of energy consumed by humanity. The key to harnessing this energy is to develop systems that can efficiently convert solar energy into usable energy. Photosynthetic organisms possess this capability, making them ideal biocatalysts to use solar energy to power production of biofuels and other energy rich compounds. My goal is to provide a framework for how we can develop photosynthetic organisms as platforms for conversion of solar energy into energy rich compounds. My research uses diverse approaches to study:
- how photosynthetic organisms adapt their photosystem and membranes to different light intensities in a process known as photoacclimation
- how redox changes that occur in response to light and nutrient limitation control metabolic processes relevant to bioenergy
- engineering photosynthetic organisms to use energy from photosynthesis to power reactions relevant to bioenergy production, such as using a remodeled nitrogenase to produce hydrocarbons.
Kathryn Fixen, Ph.D.
Current Research
Redox regulation in an anaerobe
Most studies of redox sensing and regulation by bacteria have involved aerobes and their responses to protect themselves from reactive oxygen species. By contrast very little work has explored redox sensing by anaerobes. Based on my postdoctoral work, I hypothesized that light intensity alters the cellular redox status in R. pal. To test this hypothesis, I collaborated with Dr. Aaron Wright at Pacific Northwest National Laboratories to used activity-based proteomics to identify redox-sensitive proteins. Using this approach, we found 200 redox-sensitive proteins that respond to low light intensity. These included proteins that could constitute targets for optimization of pathways important for bioenergy production. In future work, I will test the idea that changes in redox status of proteins is a posttranslational regulatory mechanism that R. pal uses to slow metabolism with rapid kinetics.
Overcoming regulatory constraints to use alternative nitrogenases to produce energy rich compounds
My work has shown that it is possible to engineer a photosynthetic organism to use a remodeled Mo-nitrogenase to reduce CO2 to CH4 using energy from light. This work was possible because we had a deep understanding of Mo-nitrogenase gene regulation and could constitutively express Mo-nitrogenase. The ability of alternative nitrogenases (containing V or Fe instead of Mo) to reduce carbon compounds is also being explored. However, regulation of these alternative nitrogenases is poorly understood. In order to engineer R. pal strains that have the potential to constitutively express an alternative nitrogenase will require understanding of their regulation. I am working to understand how alternative nitrogenases are regulated, which could provide a platform for optimizing activity of alternative nitrogenases, and allow us to broaden the ability of R. pal to carry out energy-dependent reactions involved in bioenergy.
Publications
Mailing address
Kathryn Fixen, Ph.D., Research Assistant Professor
UW Box 357735
Seattle WA 98195
Shipping address
Kathryn Fixen, Ph.D., Research Assistant Professor
HSB K-360
1705 NE Pacific St
Seattle WA 98195
kfixen@uw.edu
Contact Info