CONICET | Buscador de Institutos y Recursos Humanos

Rhizobia are Gram-negative bacteria with ability to fix atmospheric N2 insymbiotic association with the root of legumes. Current evidence shows that rhizobia carry in most cases variable number of plasmids related to their symbiosis and freeliving, being a common feature the presence of several plasmid replicons within a same strain. We has been studying the cryptic plasmids in Ensifer meliloti, and the mobilization properties of two cryptic plasmids (pSmeLPU88b and pSmeLPU88a) from the strain E. meliloti LPU88 were reported (1, 2). To further characterize pSmeLPU88b plasmid the full sequence was achieved. pSmeLPU88b was 35.9 kb in size, had an average GC % of 58.56 and 40 CDS. The replication modules were identified in silico: one belonging to the repABC type, and the other related to the repC family of plasmid replication regions. Both regionsresulted nearly identical to the homologous elements from plasmid pMBA9a present in an isolate from Canada (3). In addition, we identify downstream of the repABC system three CDS that present homologies with recombinases and with toxinantitoxin systems. The antitoxin is related to the Phd_YefM, type II toxin-antitoxin systemand the toxin belongs to PemK-like, MazF-like toxin family. It is noteworthy that the three CDS observed present the same genetic structure in pSmeLPU88band in other rhizobial plasmid (pRmeGR4a, pSMED03 pSINME01) and in all cases they are found downstream of the repABC operon.By cloning each replication system in suicide plasmids we demonstrated that any of them can support plasmid replication in the E. meliloti genetic background. Incompatibility analysis of the cloned rep systems results in the curations of the parental plasmid. Interestingly, both obtained plasmids can coexist together withoutselection.