Sinorhizobium sp. strain BL3 was isolated from the nodules of Phaseolus lathyroides plants that were found growing under saline conditions in the northeastern region of Thailand. It can tolerate up to 600 mM NaCl and is effective in N2 fixation. A genomic DNA clone library of BL3 was constructed and transferred to the salt-sensitive Rhizobium sp. strain TAL1145 by conjugation and the transconjugants were selected on medium containing 100 mM NaCl. Two hundred colonies that grew under this salt condition were isolated. From twenty-four of those colonies, two clusters of genes involved in salt tolerance were isolated. The deduced proteins encoded by the genes of first region include an ATPase, and a transcriptional regulator of AraC family, while the deduced proteins of the second region showed high similarities with enzymes involved in glycine betaine biosynthesis in Sinorhizobium meliloti. When these gene clusters were transferred to salt-sensitive Rhizobium and Bradyrhizobium, the transconjugants showed increased tolerance to salt stress. ©2006 Balaban.