Isolation and characterization of a pSym locus of Rhizobium sp. BR816 that extends nodulation ability of narrow host range Phaseolus vulgaris symbionts to Leucaena leucocephala.

Introduction of a cosmid library of megaplasmid DNA of Rhizobium sp. BR816, a broad host range Rhizobium strain, into R. etli CE3, a narrow host range bean symbiont, resulted in the isolation of a transconjugant that could effectively nodulate Leucaena leucocephala. Analysis of the corresponding cosmid, pBRF2, revealed the presence of genes required for elicting nitrogen-fixing nodules on L. leucoephala. Subcloning and Tn5 tagging identified a locus responsible for the host range extension. Sequence analysis of this locus revealed an ORF that shows significant identity with NodO of R. leguminosarum bv. viciae.