Disparate response to microoxia and nitrogen oxides of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes.
Expression of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes requires low oxygen (O2) tension and nitrate (NO3-), through a regulatory network comprised of two coordinated cascades, FixLJ-FixK2-NnrR and RegSR-NifA. To precisely understand how these signals are integrated in the FixLJ-FixK2-NnrR circuit, we analyzed β-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 fixK2and nnrR mutant backgrounds. While microoxic conditions (2% O2at headspace) were sufficient to induce expression of napEDABC and nirK genes and this control depends on FixK2, norCBQD expression requires, in addition to microoxia, nitric oxide gas (NO) and both FixK2and NnrR transcription factors. Purified FixK2protein 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 O2-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 FixK2and 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.
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: emilio.bueno@umu.se.
Emilio
E
Bueno
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: efrobles@unav.es.
Eloy F
EF
Robles
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: mariajesus.torres@eez.csic.es.
María J
MJ
Torres
Department of Environmental Protection, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008 Granada, Spain. Electronic address: tino.krell@eez.csic.es.
Tino
T
Krell
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: eulogio.bedmar@eez.csic.es.
Eulogio J
EJ
Bedmar
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: mariajesus.delgado@eez.csic.es.
María J
MJ
Delgado
Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), C/Profesor Albareda 1, E-18008, Granada, Spain. Electronic address: socorro.mesa@eez.csic.es.
Socorro
S
Mesa
D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism; D058440:Denitrification / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics*; D009589:Nitrogen Oxides / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*
D009589:Nitrogen Oxides; D010100:Oxygen
CRP/FNR transcription factors; FixK(2)-like box; NnrR; Promoter; Rhizobia; Signal molecule