Although operons are prominent features in the genomes of bacteria and archaea, the evolution and mechanisms that promote operon formation are still not resolved and a number mechanisms have been proposed [3–8]. These mechanisms involve dynamic genetic events that include gene transfer events, deletions, duplications,

and recombinations [2, 5, 8]. Since operons are prominent features in bacterial genomes, and often encode genes with metabolic potential, it may be assumed that their evolution is under some selection pressure, thus Gemcitabine molecular weight allowing prokaryotic cells to rapidly adapt, compete and grow under changing environmental conditions. The metabolic capability of an organism can be a function of its genome size and gene complement and these greatly affect its ability BIIB057 mw to live in diverse environments. The alpha subdivision of the proteobacteria includes some organisms that are very similar phylogenetically but inhabit many diverse ecological niches, including a number of bacteria that can interact with eukaryotic hosts [9]. The genome sizes of these organisms varies from about 1 MB for members of the genus Rickettsia to approximately 9 MB for members of the bradyrhizobia [10]. Comparative genomic studies of this group has led to the supposition that there has been two independent reductions in genomic size,

one which gave rise to the Brucella and Bartonella, the other which gave rise to the Rickettsia[11]. In addition, it also suggests that there has been a major genomic expansion and that roughly correlates with the soil microbes within the order Rhizobiales [11]. The genomes of Rhizobia are dynamic. Phylogenetic analysis of 26 different Sinorhizobium and Bradyrhizobium genomes recently showed that recombination has dominated the evolution of the core genome in these organisms, and that vertically transmitted genes were rare compared with genes with a Adenosine history of recombination and lateral gene transfer [12]. In this manuscript we have utilized comparative genomics in a focused manner to investigate the evolution of genes and loci involved in the catabolism of the sugar alcohols erythritol,

adonitol and L-arabitol, primarily within the alpha-proteobacteria. The number of bacterial species that are capable of selleck inhibitor utilizing the common 4 carbon polyol, erythritol, as a carbon source is restricted [13]. Catabolism of erythritol has been shown to be important for competition for nodule occupancy in Rhizobium leguminosarum as well as for virulence in the animal pathogen Brucella suis[14]. Genetic characterization of erythritol catabolic loci has only been performed in R. leguminosarum, B. abortus and Sinorhizobium meliloti. In these organ-isms erythritol is broken down to dihydroxyacetone-phosphate using the core erythritol catabolic genes eryABC-tpiB[15]. During characterization of the erythritol locus of S.