Given SC79 order that S. fredii NGR234 and M. loti each contain homologs to all of these genes, except for fucA which is not necessary for the catabolism of any of the sugars [15], it follows that these two loci may also be capable of catabolising all three polyols. It has
also been established that the B. abortus and R. leguminosarum type loci are used for erythritol catabolism, and given the annotation and degree of relatedness (E value = 0) of proteins belonging to all species in the clade, it is not expected that these loci would be capable of breaking down additional polyols [20, 21]. This is supported by the fact that the introduction of the R. leguminosarum cosmid containing the erythritol locus into S. meliloti strains unable to utilize erythritol, adonitol, and L-arabitol were unable to be complemented for growth on adonitol and L-arabitol [15]. It is however necessary to remember that some of identified loci are only correlated with polyol utilization based on our analysis and that basic biological function, such as the ability to utilize these polyols has not been previously described. With the advent of newer
generations of sequencing technologies a greater number of bacterial genomes will be sequenced. It is likely that more examples of rearrangements of catabolic loci through bacterial lineages will be observed. Since the ability to catabolize erythritol is found in relatively few bacterial Fludarabine mouse MK-4827 molecular weight species, operons that encode erythritol and other associated polyols may be ideal models to observe operon evolution. Conclusions In this work we show that there are at least three distinct erythritol/polyol loci arrangements. Two distinct
ABC transporters can be found within these within these loci and phylogenetic analysis check details suggests these should be considered analogs. Finally we provide evidence that suggest that these loci have been horizontally transferred from the alpha-proteobacteria into both the beta and gamma-proteobacteria. Acknowledgments This work was funded by NSERC Discovery Grants to IJO and GH. BAG was funded by an NSERC CGS-D. The authors would like to thank the anonymous reviewer’s suggestions that greatly improved the manuscript. Electronic supplementary material Additional file 1: Figure S1: EryA phylogenetic tree was constructed using ML and Bayesian analysis. Support for each clade is expressed as a percentage (Bayesian / ML, ie. posterior probability and bootstrap values respectively) adjacent to the nodes that supports the monophyly of various clades. The branch lengths are based on ML analysis and are proportional to the number of substitutions per site. This phylogenetic tree was used in the mirror tree in Figure 2 without branch lengths due to space restrictions. (EPS 1 MB) References 1.