An integrated biochemical system for nitrate assimilation and nitric oxide detoxification in Bradyrhizobium japonicum

Cabrera, Juan J., Salas, Ana, Torres, María J., Bedmar, Eulogio J., Richardson, David J. ORCID:, Gates, Andrew J. ORCID: and Delgado, María J. (2016) An integrated biochemical system for nitrate assimilation and nitric oxide detoxification in Bradyrhizobium japonicum. Biochemical Journal, 473 (3). pp. 297-309. ISSN 0264-6021

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Rhizobia are recognized to establish N2-fixing symbiotic interactions with legume plants. Bradyrhizobium japonicum, the symbiont of soybeans, can denitrify and grow under free-living conditions with nitrate (NO3−) or nitrite (NO2−) as sole nitrogen source. Unlike related bacteria that assimilate NO3−, genes encoding the assimilatory NO3− reductase (nasC) and NO2− reductase (nirA) in B. japonicum are located at distinct chromosomal loci. The nasC gene is located with genes encoding an ABC-type NO3− transporter, a major facilitator family NO3−/NO2− transporter (NarK), flavoprotein (Flp) and single-domain haemoglobin (termed Bjgb). However, nirA clusters with genes for a NO3−/NO2−-responsive regulator (NasS-NasT). In the present study, we demonstrate NasC and NirA are both key for NO3− assimilation and that growth with NO3−, but not NO2− requires flp, implying Flp may function as electron donor to NasC. In addition, bjgb and flp encode a nitric oxide (NO) detoxification system that functions to mitigate cytotoxic NO formed as a by-product of NO3− assimilation. Additional experiments reveal NasT is required for NO3−-responsive expression of the narK-bjgb-flp-nasC transcriptional unit and the nirA gene and that NasS is also involved in the regulatory control of this novel bipartite assimilatory NO3−/NO2− reductase pathway.

Item Type: Article
Additional Information: © 2016 Authors This is an open access article published by Portland Press Limited and distributed under the Creative Commons Attribution License 3.0.
Uncontrolled Keywords: nitrate reduction,nitrite reduction,nitric oxide reductase,bacterial hemoglobin,bacterial denitrification
Faculty \ School:

Faculty of Science > School of Biological Sciences
UEA Research Groups: Faculty of Science > Research Groups > Molecular Microbiology
Faculty of Science > Research Groups > Organisms and the Environment
Faculty of Science > Research Centres > Centre for Molecular and Structural Biochemistry
Depositing User: Pure Connector
Date Deposited: 27 Jan 2016 11:00
Last Modified: 04 May 2023 21:30
DOI: 10.1042/BJ20150880


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