The only species that contains a locus identical in content and arrangement to S. meliloti is the closely related Sinorhizobium medicae. The locus of Sinorhizobium fredii NGR234, contains all but one of the genes (fucA1) found in the other Sinorhizobium loci (Figure  2). Figure 2 The phylogenetic tree of erythritol proteins does

not correlate with species phylogeny; evidence for horizontal gene transfer. EryA phylogenetic tree (Left) and RpoD species tree (Right) were 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 AG-014699 molecular weight to the nodes that supports the monophyly of various clades. V. eiseniae was used as an outgroup for both trees since it was the most phylogenetically distant organism. A tree including branch lengths for EryA is included as Additional file 1: Figure S1. The loci of Mesorhizobium species were varied, however all three Mesorhizobium sp. contained an independent locus

with homologs to lalA and rbtBC elsewhere in the genome (Figure  1). Interestingly, while Mesorhizobium loti and Mesorhizobium opportunism both contain transporters homologous to mptABCDE, Mesorhizobium ciceri bv. biserrulae contains a transporter homologous to eryEFG. This operon also contains the same hypothetical gene that is found at the beginning of the R. leguminosarum eryEFG transcript. The transporters however, are arranged check details in a manner similar to that seen in S. meliloti and the gene encoding the regulator eryD, is found ahead of the transporter genes, whereas in R. leguminosarum and Brucella, eryD is found following eryC (Figure  1). We also note that whereas M. loti and M. opportunism both contain a putative fructose 1,6 bis phosphate aldolase gene between the eryR-tpiB-rpiB operon and eryC, a homolog to this is also gene is found adjacent

to the rpiB in Brucella. Bradyrhizobium sp. BTAi1, and ORS278, A. cryptum and V. eiseniae Isoconazole all have similar genetic arrangement to that of S. meliloti, except that they do not contain a homolog to eryC, or an associated eryR-tpiB-rpiB operon. These loci also differ primarily in their arrangement of lalA-rbtBC (Figure  1). The phylogenies of erythritol proteins do not correlate with species phylogeny The DNA sequences of 16S rDNA (data not shown) as well as the amino acid sequences of RpoD were extracted from GenBank to analyze the phylogenetic relationships of the organisms examined in this study, using the most phylogenetically distant organism Verminephrobacter eiseniae as an out-group. The results of the 16S rDNA and RpoD sequence analyses were in concordance with each other and are consistent with phylogenies that have been previously generated [42]. Initial comparison of the operon structures with the generated phylogenies suggested that the operon structure(s) did not correlate with the species phylogeny.