leguminosarum bv. viciae, R. etli and R. leguminosarum bv. trifolii [16]. The chosen name “”chromid-like”"

(as opposed to simply “”chromid”") was the result of data scarcity concerning their gene content, insufficient to justify the name “”chromid”" [16]. Moreover, it is known that genes of the repABC operon are peculiar genetic markers because of the complex phylogeny of particular Ulixertinib molecular weight genes within the operon, whose evolutionary history could not be strictly connected with other genes of particular replicons [13]. In the study of the distribution of several chromosomal and plasmid markers within a group of 23 nodule isolates, stable genes permanently located in a specific R. leguminosarum bv. trifolii genome compartment: chromosome, chromid-like and ‘other plasmids’ including pSym were distinguished. Unstable genes (fixGH, thiC, acdS, pssM and Pss-V region) that changed their location at various rates or were lost from the genome were also detected. Only two of the sampled 23 strains possessed all the studied markers. A majority of strains differed in the gene content and check details gene distribution, supporting the hypothesis of the pangenomic structure of R. leguminosarum, in

which each strain of a given species contains, besides the core genome, additional genetic information specific for the strain [11, 17, 18, 39]. The distribution Morin Hydrate of the plasmid replication-find more partition genes was even more dynamic than that of genes not connected with replication. Independent transfer events of repA and repC genes of the putative repABC operon were frequently observed, especially in the ‘other plasmids’ compartment, which confirmed different evolutionary pathways for various elements of the repABC operon, recently

evidenced in Alphaproteobacteria [13]. Such considerable dynamics of replication/partition gene distribution in Rhizobium may account for changes in the plasmid number and, consequently, gene content observed in the sampled population. Beside the dynamics of replication/partition gene distribution, some level of conservation of replication genes, especially those of chromid-like replicons, was also observed. It was reflected in positive hybridizations with pRleTA1d and pRleTA1b derived rep probes, to the respective replicons of Rlt strains. One could speculate that the conservation of replication genes of chromid-like replicons may be related with their distinct properties e.g. stability. However, the gene content rather than the properties of the replication system, resulting e.g. from conservation of replication genes, seem to be crucial for replicon stability [40]. Redistribution of genes between the different genome compartments could further trigger their sequence divergence under different selective pressures [13, 15, 41].