The path of electron transfer to nitrogenase in a phototrophic alpha-proteobacterium

Kathryn R. Fixen, Nilanjan Pal Chowdhury, Marta Martinez-Perez, Saroj Poudel, Eric S. Boyd, Caroline S. Harwood

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


The phototrophic alpha-proteobacterium, Rhodopseudomonas palustris, is a model for studies of regulatory and physiological parameters that control the activity of nitrogenase. This enzyme produces the energy-rich compound H2, in addition to converting N2 gas to NH3. Nitrogenase is an ATP-requiring enzyme that uses large amounts of reducing power, but the electron transfer pathway to nitrogenase in R. palustris was incompletely known. Here, we show that the ferredoxin, Fer1, is the primary but not sole electron carrier protein encoded by R. palustris that serves as an electron donor to nitrogenase. A flavodoxin, FldA, is also an important electron donor, especially under iron limitation. We present a model where the electron bifurcating complex, FixABCX, can reduce both ferredoxin and flavodoxin to transfer electrons to nitrogenase, and we present bioinformatic evidence that FixABCX and Fer1 form a conserved electron transfer pathway to nitrogenase in nitrogen-fixing proteobacteria. These results may be useful in the design of strategies to reroute electrons generated during metabolism of organic compounds to nitrogenase to achieve maximal activity.

Original languageEnglish (US)
Pages (from-to)2500-2508
Number of pages9
JournalEnvironmental microbiology
Issue number7
StatePublished - Jul 2018

Bibliographical note

Funding Information:
This work was supported as part of the Biological Electron Transfer and Catalysis Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012518.

Publisher Copyright:
© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd


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