Bradyrhizobium japonicum cytochrome c550 is required for nitrate respiration but not for symbiotic nitrogen fixation

• Published in: Journal of Bacteriology Vol. 177; no. 8; pp. 2214 - 2217
• Main Authors: Bott, M. (Eidgenossische Technische Hochschule, Aurich, Switzerland.), Thony-Meyer, L, Loferer, H, Rossbach, S, Tully, R.E, Keister, D, Appleby, C.A, Hennecke, H
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.04.1995
• Subjects: Amino Acid Sequence; Bacteriology; Base Sequence; BRADYRHIZOBIUM; CADENA RESPIRATORIA; CHAINE RESPIRATOIRE; CITOCROMO C; Cloning, Molecular; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CYTOCHROME C; Cytochrome c Group - genetics; Cytochrome c Group - metabolism; DNA, Bacterial - genetics; Electron Transport; FIJACION DEL NITROGENO; FIXATION DE L'AZOTE; GENE; GENES; Genes, Bacterial; Genetic Complementation Test; GLYCINE MAX; Glycine max - metabolism; Glycine max - microbiology; Molecular Sequence Data; Mutation; NITRATE; Nitrates; Nitrates - metabolism; NITRATOS; Nitrogen; Nitrogen Fixation - genetics; Nitrogen Fixation - physiology; NODOSITE RACINAIRE; NUDOSIDADES RADICULARES; OXIRREDUCION; OXYDOREDUCTION; Proteins; RESPIRACION; RESPIRATION; Restriction Mapping; Rhizobiaceae - genetics; Rhizobiaceae - growth & development; Rhizobiaceae - metabolism; SECUENCIA NUCLEICA; SEQUENCE NUCLEIQUE; Symbiosis - genetics; Symbiosis - physiology
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.177.8.2214-2217.1995

Bradyrhizobium japonicum possesses three soluble c-type cytochromes, c550, c552, and c555. The genes for cytochromes C552 (cycB) and c555 (cycC) were characterized previously. Here we report the cloning, sequencing, and mutational analysis of the cytochrome c550 gene (cycA). A B. japonicum mutant with an insertion in cycA failed to synthesize a 12-kDa c-type cytochrome. This protein was detectable in the cycA mutant complemented with cloned cycA, which proves that it is the cycA gene product. The cycA mutant, a cycB-cycC double mutant, and a cycA-cycB-cycC triple mutant elicited N2-fixing root nodules on soybean (Nod+ Fix+ phenotype); hence, none of these three cytochromes c is essential for respiration supporting symbiotic N2 fixation. However, cytochrome c550, in contrast to cytochromes c552 and c555, was shown to be essential for anaerobic growth of B. japonicum, using nitrate as the terminal electron acceptor