GENETIC-CHARACTERIZATION OF RHIZOBIUM SP STRAIN TAL1145 THAT NODULATES TREE LEGUMES

Rhizobium sp. strain TAL1145 nodulates Leucaena leucocephala and Phase olus vulgaris, in addition to a wide range of tropical tree legumes. S ix overlapping clones that complemented nodulation defects in leucaena and bean rhizobia were isolated and a 40-kb map of the symbiosis regi on was constructed. The common nod and nifA genes were situated approx imately 17 kb apart, with the nodlJ genes in between. These clones ena bled a derivative of TAL1145 carrying a partially deleted pSym to form ineffective nodules on both leucaena and bean, and a similar derivati ve of Rhizobium etli TAL182 to form ineffective nodules on bean. When two representative clones, pUHR9 and pUHR114, were each transferred to wild-type rhizobial strains, they allowed ineffective nodulation by R hizobium meliloti on both leucaena and bean and by Rhizobium leguminos arum bv. viciae on bean. Transconjugants of R. leguminosarum bv. trifo lii formed effective nodules on leucaena and ineffective nodules on be an. Tn5 mutagenesis of the symbiosis region resulted in a variety of n odulation and fixation phenotypes on leucaena and bean. On the basis o f 16S rRNA sequences, TAL1145 was found to be distinct from both R. tr opici and NGR234, the two groups of leucaena symbionts that were previ ously described.