Modern agriculture is critically dependent on fertilizers as the source of biologically available nitrogen. Chemical synthesis of fertilizers is energy intensive, and the process generates greenhouse gases that are a major driver of climate change. Moreover, application of fertilizers invariably leads to run-off related issues that are detrimental to the environment. One potential solution is development of nitrogen-fixing crop plants. This is a grand challenge in biology, since oxygen is a potent inhibitor of nitrogenase, the enzyme that catalyzes nitrogen fixation. Oxygenic photosynthetic organisms are the primary producers of oxygen in the biosphere. Among them, some cyanobacterial strains can also fix nitrogen using the energy captured during photosynthesis. The central objective of this project is to develop a deep understanding of the biological system in cyanobacteria that accommodates the two antagonistic processes, photosynthesis and nitrogen fixation. Success in these efforts will unravel design principles to develop nitrogen-fixing crop plants and will have far reaching implications in basic biology as well as biotechnology. The project activities also include (i) providing training for local and international undergraduate students and (ii) outreach activities for scientifically underprivileged individuals, organized by the International Center for Energy, Environment and Sustainability at Washington University.
Unicellular diazotrophic cyanobacteria are the only cellular platforms in which oxygenic photosynthesis and nitrogen fixation coexist. These microbes have developed sophisticated strategies to perform these antagonistic processes in the same cell by temporally separating them. Cyanobacteria are the only prokaryotes with a well characterized circadian clock that is thought to coordinate these two processes. However, a detailed understanding of the molecular mechanisms by which these organisms adjust their metabolism to accommodate both nitrogen fixation and photosynthesis is lacking. The plan is to use a recently developed genetic modification system for the unicellular diazotrophic strain Cyanothece sp. ATCC 51142 to strategically probe these questions. During this project, a systems biology approach is deployed to dissect the regulatory hierarchies that coordinate photosynthesis and nitrogen fixation. Overall, these studies help unlock the puzzle of the integration of photosynthesis and nitrogen fixation in a single cell. They provide a quantitative map of the highly orchestrated changes occurring during the day-night diel cycle informing how regulatory events affect metabolism as well as how the products of metabolism reset regulation.
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.