Identification of nifE-, nifN- and nifS-like genes in Bradyrhizobium japonicum |
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Authors: | Sabine Ebeling Matthias Hahn Hans-Martin Fischer and Hauke Hennecke |
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Institution: | (1) Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, Universitätsstraße 2, CH-8092 Zürich |
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Abstract: | Summary The 17 kb region between the Bradyrhizobium japonicum nitrogenase genes (nifDK and nifH) was investigated for the presence of further nif or fix genes by site-directed insertion or deletion/replacement mutagenesis and interspecies hybridization. Mutant strains were tested for their ability to reduce acetylene in free-living, microaerobic culture (Nif phenotype) and in soybean root nodules (Fix phenotype). The presence of a gene, previously identified by hybridization with the Klebsiella pneumoniae nifB gene, was proved by isolation of a nifB insertion mutant which was completely Nif- and Fix-. Three other regions were found to be homologous to the K. pneumoniae genes nifE, nifN, and nifS, NifE and nifN insertion mutants were completely Nif-/Fix- whereas nifS mutants were leaky with 30% residual Fix activity. Taken together, the data show that the B. japonicum genome harbours a cluster of closely adjacent genes which are directly concerned with nitrogenase function. |
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Keywords: | Bradyrhizobium Nif genes Nitrogen fixation Root nodule symbiosis |
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