Kathryn Fixen
Office Address

750 Biological Sciences
St. Paul, MN 55108
United States



Assistant Professor
Plant and Microbial Biology

How do bacteria control electron flow inside the cell and how can we tap into this reducing power for biotechnological purposes? In the Fixen lab, we are working to understand intracellular electron flow in the anoxygenic phototroph, Rhodopseudomonas palustris (R. pal). R. pal can use energy from sunlight and reducing power generated from organic compounds such as lignin to make energy-rich compounds like hydrogen and methane using the enzyme nitrogenase. To understand intracellular electron flow in R. pal, we are working to characterize components of electron transfer and understand how the components are regulated by changes in the environment. Ongoing projects in the lab include 1) understanding the role of redox regulation in controlling electron flow in an anaerobe, and 2) the role and regulation of electron carrier proteins in an anoxygenic phototroph. By understanding intracellular electron transfer, we hope to find ways to direct electrons towards producing large amounts of energy-rich, reduced compounds like hydrogen.

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Selected publications

  • K.R. Fixen, Y. Oda, and C.S. Harwood. (2019). Redox regulation of a light-harvesting antenna complex in an anoxygenic phototroph. mBio. 10(6):e02838-19. doi:10.1128/mBio.02838-19.
  • K.R. Fixen, N.P. Chowdhury, M. Martinez-Perez, S. Poudel, E.S. Boyd, and C.S. Harwood. (2018). The path of electron transfer to nitrogenase in a phototrophic alpha-proteobacterium. Environ. Microbiol. 20(7):2500-2508. doi: 10.1111/1462-2920.14262.
  • K.R. Fixen, N.P. Chowdhury, M. Martinez-Perez, S. Poudel, E.S. Boyd, and C.S. Harwood. (2018). The path of electron transfer to nitrogenase in a phototrophic alpha-proteobacterium. Environ. Microbiol. In press. doi: 10.1111/1462-2920.14262. 
  • S. Poudel, D.R. Colman, K.R. Fixen, R.N. Ledbetter, Y. Zheng, N. Pence, L.C. Seefeldt, J.W. Peters, C.S. Harwood, and E.S. Boyd. (2018). Electron transfer to nitrogenase in different genomic and metabolic backgrounds. J. Bacteriol. In press. doi: 10.1128/JB.00757-17. 
  • Y. Zheng, D.F. Harris, Z. Yu, Y. Fu, S. Poudel, R.N. Ledbetter, K.R. Fixen, Z.Y. Yang, E.S. Boyd, M.E. Lidstrom, L.C. Seefeldt, and C.S. Harwood. (2018). A pathway for biological methane production using iron-only nitrogenase. Nat. Microbiol. 3(3): 281-286. doi: 10.1038/s41564-017-0091-5. 
  • A. Garcia-Costas, S. Poudel, A.F. Miller, G.J. Schut, R.N. Ledbetter, K.R. Fixen, L.C. Seefeldt, M.W.W. Adams, C.S. Harwood, E. Boyd , and J.W. Peters. (2017). Defining electron bifurcation in the electron transferring flavoprotein family. J Bacteriol. 199(21): e00440-17. DOI: 10.1128/JB.00440-17 
  • J. Yang, L. Yin, F.H. Lessner, E.S. Nakayasu, S.H. Payne, K.R. Fixen, L. Gallagher, and C.S. Harwood. (2017). Genes essential for phototrophic growth by a purple alphaproteobacterium. Environ. Microbiol. 19(9): 3567-3578. doi: 10.1111/1462-2920.13852 
  • K.R. Fixen*, S.R. Starkenburg*, C.S. Harwood, and R.A. Cattolico. (2016) Draft genomes of 8 bacterial isolates associated with the haptophyte Chrysochromulina tobin. Genome Announc. 4(6). pii: e01162-16. doi: 10.1128/genomeA.01162-16.  *contributed equally to this work 
  • K.R. Fixen*, Y. Zheng*, D.F. Harris, S. Shaw, Z.Y. Yang, D.R. Dean, L. Seefeldt, and C.S. Harwood. (2016). Light-driven carbon dioxide reduction to methane by nitrogenase in a photosynthetic bacterium. PNAS. In press. doi:10.1073/pnas.1611043113.  *contributed equally to this work 
  • K.R. Fixen and C.S. Harwood. (2016). A polymorphism in the oxygen-responsive repressor PpsR2 confers a growth advantage to the purple nonsulfur bacterium Rhodopseudomonas palustris under low light. Photosynth Res. 129: 199. doi:10.1007/s11120-016-0288-0 
  • K.R. Fixen*, Y. Oda*, and C.S. Harwood. (2015). Clades of photosynthetic bacteria belonging to the genus Rhodopseudomonas show marked diversity in light-harvesting antenna complex gene composition and expression. mSystems. 1(1): e00006-15. doi: 10.1128/mSystems.00006-15. 
  • K.R. Fixen, A.W. Baker, E.A. Stojkovic, J.T. Beatty, C.S. Harwood. (2014). Apo-bacteriophytochromes modulate bacterial photosynthesis in response to low light. PNAS. 111(2): E237-44. doi: 10.1073/pnas.1322410111