Characterization of the fixABC region of Azorhizobium caulinodans ORS571 and identification of a new nitrogen fixation gene |
| |
Authors: | P Alexandre Kaminski Françoise Norel Nicole Desnoues Anil Kush Giovanni Salzano and Claudine Elmerich |
| |
Institution: | (1) Unité de Physiologie Cellulaire, Département des Biotechnologies, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France;(2) Present address: Unité des Entérobactéries, Institut Pasteur, F-75724 Paris Cedex 15, France;(3) Present address: Institute of Molecular Cell Biology, National University of Singapore, Kent Ridge Road, 0511, Singapore;(4) Present address: Istituto di Microbiologia Agraria, Facolta di Agraria, Universita di Napoli, Porpici Napoli, Italy |
| |
Abstract: | Summary The fast growing strain, Azorhizobium caulinodans ORS571, isolated from stem nodules of the tropical legume Sesbania rostrata, can grow in the free-living state at the expense of molecular nitrogen. Five point mutants impaired in nitrogen fixation in the free-living state have been complemented by a plasmid containing the cloned fix-ABC region of strain ORS571. Genetic analysis of the mutants showed that one was impaired in fixC, one in fixA and the three others in a new gene, located upstream from fixA and designated nifO. Site-directed Tn5 mutagenesis was performed to obtain Tn5 insertions in fixB and fixC. The four genes are required for nitrogen fixation both in the free-living state and under symbiotic conditions. The nucleotide sequence of nifO was established. The gene is transcribed independently of fixA and does not correspond to fixX, recently identified in Rhizobium meliloti and R. leguminosarum. Biochemical analysis of the five point mutants showed that they synthesized normal amounts of nitrogenase components. It is unlikely that fixA, fixC and nifO are involved in electron transport to nitrogenase. FixC could be required for the formation of a functional nitrogenase component 2. |
| |
Keywords: | Azorhizobium caulinodans Nitrogen fixation fixABC gene nifO Nitrogenase activity |
本文献已被 SpringerLink 等数据库收录! |
|