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.

Journal Article Mapping and nucleotide sequence of the nifS promoter of Bradyrhizobium japonicum Get access Sabine Ebeling, Sabine Ebeling Search for other works by this author on: Oxford Academic PubMed Google Scholar John D. Noti, John D. Noti 1The Boyce Thompson Institute for Plant Research, Cornell UniversityIthaca, NY 14853, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Hauke Hennecke Hauke Hennecke * *To whom correspondence should be addressed Search for other works by this author on: Oxford Academic PubMed Google Scholar Nucleic Acids Research, Volume 15, Issue 22, 25 November 1987, Page 9598, https://doi.org/10.1093/nar/15.22.9598 Published: 25 November 1987 Article history Received: 20 October 1987 Published: 25 November 1987

Bradyrhizobium japonicum is a member of the slow-growing genus of the rhizobia. It is able to form determinate, N2 fixing root nodules on soybean (Glycine max L. Merr.). Research in our laboratory is concerned with the structural and functional analysis of bacterial genes involved in nodulation and symbiotic nitrogen fixation. We have chosen B. japonicum strain 110 for this study, as this strain is able to derepress nitrogenase activity under free-living, microaerobic growth conditions (ex planta). In this report we describe some promising mutants of B. japonicum which are defective in different steps during bacteroid and root nodule development. Furthermore, we present a progress report on the isolation and characterization of B. japonicum nod genes.