Identification and functional analysis of recent IS transposition events in rhizobia.

Rhizobia are alpha- and beta- Proteobacteria that, through the establishment of symbiotic interactions with leguminous plants, are able to fix atmospheric nitrogen as ammonium. The successful establishment of a symbiotic interaction is highly dependent on the availability of nitrogen sources in the soil, and on the specific rhizobia strain. Insertion sequences (ISs) are simple transposable genetic elements that can move to different locations within the host genome and are known to play an important evolutionary role, contributing to genome plasticity by acting as recombination hot-spots, and disrupting coding and regulatory sequences. Disruption of coding sequences may have occurred either in a common ancestor of the species or more recently. By means of ISComapare, we identified Differentially Located ISs (DLISs) in nearly related rhizobial strains of the genera Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium. Our results revealed that recent IS transposition could have a role in adaptation by enabling the activation and inactivation of genes that could dynamically affect the competition and survival of rhizobia in the rhizosphere. Abbreviated summary: Using ISCompare we identified Differentially Located Insertion Sequences (DLISs) in a diversity of rhizobial strains of agronomical relevance. We found that DLISs tend to be inserted more frequently within intergenic regions. However we found a considerable proportion in the neighborhood of promoter regions and within coding sequences. Although a small number of DLISs were found in each strain, these results suggest that gene disruption by DLISs could play a role in environmental adaptation. [ABSTRACT FROM AUTHOR]