Plasmids that insert into the rhamnose utilization locus, rha: a versatile tool for genetic studies in Sinorhizobium meliloti.

Described is a suite of plasmids that can be used to deliver DNA into a specific site in the chromosome of Sinorhizobium meliloti with a minimal impact in the physiology of the organism. This allows stable, single-copy, insertions of DNA while maintaining a constant chromosomal context. The plasmids integrate into rhaS, one of a group of genes encoding proteins for rhamnose utilization, enabling a simple screening method for recombinants, while leaving other cellular processes unaffected by the insertion. Construction of plasmids for gfp labeling, mutant complementation, gene expression and protein over-expression studies are outlined. The rha insertion plasmids constitute a flexible and easy to use collection of cloning vectors that can be efficiently delivered by conjugation or transformation, and that could be used in genetic and physiology studies of S. meliloti, and, with minor modifications, in other bacterial species.