Genomic analysis of orthologs in Rhizobiales

With the appearance of genomic sequences of Rhizobium -related organisms, we initiated a study that tried to define whether exists a relationship between gene order conservation (or synteny) and function. Therefore, the chromosomal genes of the Rhizobiales Sinorhizobium meliloti , Mesorhizobium loti , Agrobacterium tumefaciens and Brucella melitensis were classified. These organisms display a great versatility in their living styles, since both first are legume symbionts, the third is a pathogen for plants and the last is an animal pathogen. Also, their genomes show variability and, in the same order, they present two megaplasmids, a linear chromosome, a large chromosome with almost 7000 genes and a circular "accessory" chromosome, respectively. When we analyzed them, we found they share a great amount of genes, approximately 2000, the majority have a conserved position in the chromosomes (it is, they are
syntenic), they are organized in groups and operons, they encode house-keeping functions and also present a high level of sequence identity (in pairs, and compared between species). These genes, besides reflecting a relatedness among the species, and the remains of an ancient, common chromosome, also code the typical metabolic functions of the group. We extended our analysis to the Enterobacteriales (gamma proteobacteria) as Escherichia coli, Salmonella typhimurium and Erwinia carotovora and found similar tendencies in gene organization, functional linkage and essential role for syntenic genes. We consider that our synteny approach represents an interesting contribution to the analysis of the bacterial genomes, because the resulting evidences of phylogenetic, structural and functional relationships among chromosomal genes of related organisms.