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Zackry Stevenson

January 28, 2022

Student: Zackry Stevenson, graduate student in Microbiology, Iowa State University
Faculty Advisor: Dr. Elizabeth Swanner

Molybdenum demands for nitrogen fixation in the freshwater Fe(II)-oxidizing phototroph “Ca. Chlorobium masyuteum”

My current work involves determining the biological metal demands of nitrogen fixation funded by an inaugural NASA Interdisciplinary Consortia for Astrobiology Research ICAR. My project will determine the threshold of Molybdenum (Mo) concentrations necessary for nitrogen fixation using the Fe-Mo containing nitrogenase in anoxygenic photosynthetic bacterium to augment what is known from a few culture studies of diazotrophic Cyanobacteria. Several studies have found that nitrogen fixation is limited at low Mo thresholds in freshwater heterocystous diazotrophic cultures. It is unclear if these findings a
e relevant to diverse natural microbial communities, including diazotrophic microbes such as anoxygenic photosynthetic bacteria. These organisms were thought to be significant primary producers on the early Earth, but the oceans at this time contained far less Mo due to the lack of oxygen in the atmosphere and minimal oxidative weathering. We will study Fe-Mo nitrogenase activity as a function of Mo concentration gradients within modern meromictic lakes that are analogs to early anoxic oceans. This work addresses the co-evolution of life and physical environments by probing the metal availabilities and the natural selection of elements by vital biogeochemical processes. Lastly, this work would help relate to the NASA mission in particular the Space Technology Mission Directorate, by establishing how metal availability might be useful as a criterium for nitrogen fixation to sustain a biosphere, which can inform interpretation of data from current missions on Mars (e.g., Mars Science Laboratory on Curiosity, Perseverance).

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