title: Characterization of the norCBQD genes, encoding nitric oxide reductase, in the nitrogen fixing bacterium Bradyrhizobium japonicum.
abstract: The genes norCBQD that encode the bc-type nitric oxide reductase from Bradyrhizobium japonicum USDA110 have been isolated and characterized. norC and norB encode the cytochrome c-containing subunit II and cytochrome b-containing subunit I of nitric oxide reductase, respectively. norQ encodes a protein with an ATP/GTP-binding motif, and the predicted norD gene product shows similarity with NorD from other denitrifiers. Mutational analysis indicates that the two structural norC and norB genes are required for microaerobic growth under nitrate-respiring conditions. A mutant strain lacking a functional norC gene also lacked the 16 kDa c-type cytochrome that is normally detectable by haem-staining of proteins from membranes of microaerobically grown wild-type cells. Expression of a transcriptional fusion of the nor promoter region to the reporter gene lacZ (P(norC)-lacZ) was not detected in aerobically grown cells of USDA110, but the fusion was induced threefold when the cells were cultured under microaerobic conditions (1% O(2)) with either nitrite or nitric oxide, and about 18-fold when nitrate was the N oxide present in the medium. The P(norC)-lacZ fusion was not expressed in the B. japonicum fixK(2) mutant strain 9043, but complementation of the mutant with the fixK(2) gene restored beta-galactosidase activity to levels similar to those found in the parental strain. The promoter region of the norCBQD genes has been characterized by primer extension. A major transcript initiates 45.5 bp downstream of the centre of a putative binding site for the transcription factor FixK(2).
authors.affiliation: Departamento de Microbiologı́a del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidı́n, CSIC, E-18080 Granada, Spain1.
authors.forename: Socorro
authors.initials: S
authors.lastname: Mesa
authors.affiliation: Centro de Investigación y Formación Hortı́cola.E-04700 El Ejido, Almerı́a, Spain2.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Velasco
authors.affiliation: Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, UK3.
authors.forename: Maximino E
authors.initials: ME
authors.lastname: Manzanera
authors.affiliation: Departamento de Microbiologı́a del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidı́n, CSIC, E-18080 Granada, Spain1.
authors.forename: Marı A J
authors.initials: MAJ
authors.lastname: Delgado
authors.affiliation: Departamento de Microbiologı́a del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidı́n, CSIC, E-18080 Granada, Spain1.
authors.forename: Eulogio J
authors.initials: EJ
authors.lastname: Bedmar
mesh_terms: D001483:Base Sequence; D020369:Bradyrhizobium / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D009586:Nitrogen Fixation / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D012329:RNA, Bacterial / Q000032:analysis
chemical_list: D012329:RNA, Bacterial; D010088:Oxidoreductases; C034747:nitric-oxide reductase