loti R7A and MAFF303099 has shown that T4SS is involved in the symbiosis stabilization, increasing or decreasing the nodulation phenotype, according to the host involved [53]. The homologous proteins of virB, AvhB8, AvhB9, and AvhB10 genes identified in R. tumefaciens and VirB8, VirB9, and VirB10 of E. meliloti are located on plasmids. Although there is a considerable Capmatinib supplier synteny between R. tumefaciens

and E. meliloti chromosomes [5, 26], conservation in the gene order among the plasmids of these microorganisms is not expected, due to the high frequency of horizontal gene transfer between plasmids of species of the Rhizobiales order. However, the grouping observed between the symbiont E. meliloti and the pathogen R. tumefaciens in the reconstruction trees generated with VirB8, VirB9, and VirB10 is in agreement with the GDC-0941 molecular weight topologies of VirB/Trb presented by Frank et al. (2005) [54], which examined

the functional divergence and horizontal transfer of the T4SS. According to these authors, the coexistence of the AvhB conjugation protein with VirB translocation effectors in the same clade, as well as the location of these proteins in plasmids and the presence of multiple copies in some species, is indicative of the occurrence of multiple events of horizontal gene transfer, the process believed to be responsible for spreading the virB operon Carnitine palmitoyltransferase II between the alpha-Proteobacteria, representing the dominant mechanism in the evolution of the conjugation PU-H71 purchase systems for secretion. Regarding the proximity of the X. autotrophicus with R. radiobacter, and of Bradyrhizobium BTAi1 with

B. quintana or R. vitis, there is no data in the literature that could allow inferences about such relationships. In these organisms, the virB operon is located between hypothetical and Tra conjugation proteins (data not shown). However, proteins involved in integration, transposition, and/or DNA recombination were not identified close to VirB8, VirB9, and VirB10 (database), which might allow inferences that these genes could have arisen from horizontal gene transfer. Conclusions In this study, the genomic comparison has shown that symbiotic and pathogenic bacteria belonging to the order Rhizobiales may share several similar strategies of host interaction, inference taken from the high similarity on several proteins identified – e.g., FixNOPQ, NodN and VirB8910. However, it should be noted that some common clusters obtained are formed by protein families which may possess different functions in each process. The presence of symbiotic and virulence genes in both pathogens and symbionts does not seem to be the only determinant factor for lifestyle evolution in these microorganisms, although they may act in common stages of host infection.