Syntenic arrangements of the surface polysaccharide biosynthesis genes in Rhizobium leguminosarum.

We applied a genomic approach in the identification of genes required for the biosynthesis of different polysaccharides in Rhizobium leguminosarum bv. trifolii TA1 (RtTA1). Pulsed-field gel electrophoresis analyses of undigested genomic DNA revealed that the RtTA1 genome is partitioned into a chromosome and four large plasmids. The combination of sequencing of RtTA1 library BAC clones and PCR amplification of polysaccharide genes from the RtTA1 genome led to the identification of five large regions and clusters, as well as many separate potential polysaccharide biosynthesis genes dispersed in the genome. We observed an apparent abundance of genes possibly linked to lipopolysaccharide biosynthesis. All RtTA1 polysaccharide biosynthesis regions showed a high degree of conserved synteny between R. leguminosarum bv. viciae and/or Rhizobium etli. A majority of the genes displaying a conserved order also showed high sequence identity levels.