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Disparate response to microoxia and nitrogen oxides of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes
Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). CSIC, Estac Expt Zaidin, Dept Soil Microbiol & Symbiot Syst, C Profesor Albareda 1, E-18008 Granada, Spain.
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2017 (English)In: Nitric oxide, ISSN 1089-8603, E-ISSN 1089-8611, Vol. 68, 137-149 p.Article in journal (Refereed) Published
Abstract [en]

Expression of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes requires low oxygen (O-2) tension and nitrate (NO3), through a regulatory network comprised of two coordinated cascades, FixLJ-FixK(2)-NnrR and RegSR-NifA. To precisely understand how these signals are integrated in the FixLJ-FixK(2)-NnrR circuit, we analyzed beta-Galactosidase activities from napE-lacZ, nirK-lacZ and norC-lacZ fusions, and performed analyses of NapC and NorC levels as well as periplasmic nitrate reductase (Nap) activity, in B. japonicum wildtype and fixK(2) and nnrR mutant backgrounds. While microoxic conditions (2% O-2 at headspace) were sufficient to induce expression of napEDABC and nirK genes and this control depends on FixK(2), norCBQD expression requires, in addition to microoxia, nitric oxide gas (NO) and both FixK(2) and NnrR transcription factors. Purified FixK(2) protein directly interacted and activated transcription in collaboration with B. japonicum RNA polymerase (RNAP) from the napEDABC and nirK promoters, but not from the norCBQD promoter. Further, recombinant NnrR protein bound exclusively to the norCBQD promoter in an O-2-sensitive manner. Our work suggest a disparate regulation of B. japonicum denitrifying genes expression with regard to their dependency to microoxia, nitrogen oxides (NOx), and the regulatory proteins FixK(2) and NnrR. In this control, expression of napEDABC and nirK genes requires microoxic conditions and directly depends on FixK2, while expression of norCBQD genes relies on NO, being NnrR the candidate which directly interacts with the norCBQD promoter. 

Place, publisher, year, edition, pages
ACADEMIC PRESS INC ELSEVIER SCIENCE , 2017. Vol. 68, 137-149 p.
Keyword [en]
CRP/FNR transcription factors, FixK(2)-like box, NnrR, Promoter, Rhizobia, Signal molecule
National Category
Microbiology in the medical area
Identifiers
URN: urn:nbn:se:umu:diva-138212DOI: 10.1016/j.niox.2017.02.002ISI: 000405978000015OAI: oai:DiVA.org:umu-138212DiVA: diva2:1134326
Available from: 2017-08-18 Created: 2017-08-18 Last updated: 2017-08-18Bibliographically approved

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Bueno, Emilio
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