Random Tn 5 mutagenesis was used to isolate two independent Azorhizobium sesbaniae ORS571 mutants disturbed in ammonium assimilation (Asm-). Both Asm- mutant strains were shown to lack NADPH-glutamate synthase (NADPH-GOGAT) activity and to carry Tn 5 insertions ca. 1.5 kb apart in the ORS571 chromosome. The Tn 5-containing region of one of the GOGAT- mutant strains was cloned in pACYC184 and used to identify the wild-type glt (GOGAT) locus in a phage clone bank of ORS571. The cloned region was shown to have DNA homology with the Escherichia coli glt locus and to complement the Asm- phenotype of E. coli and ORS571 GOGAT- strains. The ORS571 GOGAT- mutations were found to interfere with free-living as well as symbiotic nitrogen fixation. Expression of ORS571 NADPH-GOGAT activity was shown to be independent of the nitrogen regulation (ntr) system.
- Azorhizobium sesbaniae ORS571
- Glutamate synthase
- Nitrogen fixation/assimilation
- Transposon Tn 5 mutagenesis
ASJC Scopus subject areas