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., Gates, Andrew J. 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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Abstract

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 Faculty of Science > Research Groups > Wolfson Centre for Advanced Environmental Microbiology
Depositing User:	Pure Connector
Date Deposited:	27 Jan 2016 11:00
Last Modified:	15 Jul 2025 18:33
URI:	https://ueaeprints.uea.ac.uk/id/eprint/56786
DOI:	10.1042/BJ20150880

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