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Updated: Sep 25, 2026

Transforming, Genome Editing and Phenotyping the Nitrogen-fixing Tropical Cannabaceae Tree Parasponia andersonii
Published on: August 18, 2019
Bradyrhizobium japonicum NnrR, a denitrification regulator, expands the FixLJ-FixK2 regulatory cascade
Socorro Mesa1, Eulogio J Bedmar, Astrid Chanfon
1Institute of Microbiology, Eidgenössische Technische Hochschule, CH-8092 Zürich, Switzerland. mesam@micro.biol.ethz.ch
Abstract:
In Bradyrhizobium japonicum, a gene named nnrR was identified which encodes a protein with high similarity to FNR/CRP-type transcriptional regulators. Mutant strains carrying an nnrR null mutation were unable to grow anaerobically in the presence of nitrate or nitrite, and they lacked both nitrate and nitrite reductase activities. Anaerobic activation of an nnrR'-'lacZ fusion required FixLJ and FixK(2). In turn, N oxide-mediated induction of nir and nor genes encoding nitrite and nitric oxide reductase, respectively, depended on NnrR. Thus, NnrR expands the FixLJ-FixK(2) regulatory cascade by an additional control level which integrates the N oxide signal required for maximal induction of the denitrification genes.
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