The Rhizobium etli argC gene is essential for arginine biosynthesis and nodulation of Phaseolus vulgaris

A Tn5-induced mutant strain (CTNUX5) of Rhizobium etli unable to grow with ammonium as the sole nitrogen source was isolated and characterized, Sequen ce analysis showed that Tn5 is inserted into an argC-homologous gene. Unlik e its wild-type parent (strain CE3), the mutant strain CTNUX5 had an absolu te dependency on arginine to grow. The argC gene was cloned from the wild-t ype strain CE3, and the resulting plasmid, pAR207, after transformation was shown to relieve the arginine auxotrophy of strain CTNUX5. Unlike strain C E3 or CTNUX5-pAR207, strain CTNUX5 showed undetectable levels of N-acetyl-g amma -glutamylphosphate reductase activity. Unless arginine was added to th e growth medium, strain CTNUX5 was unable to produce flavonoid-inducible li po-chitin oligosaccharides (nodulation factors) and to induce nodules or no dulelike structures on the roots of Phaseolus vulgaris.