Characterization of an accessory plasmid of Sinorhizobium meliloti and its two replication-modules

LUCHETTI A; CASTELANI L.; TOSCANI M.; LAGARES A.; DEL PAPA M.F; TORRES TEJERIZO G; PISTORIO M

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2023

1932-6203

Rhizobia are Gram-negative bacteria known for their ability to fix atmospheric N2 in symbiosiswith leguminous plants. Current evidence shows that rhizobia carry in most cases a variablenumber of plasmids, containing genes necessary for symbiosis or free-living, acommon feature being the presence of several plasmid replicons within the same strain. Formany years, we have been studying the mobilization properties of pSmeLPU88b from thestrain Sinorhizobium meliloti LPU88, an isolate from Argentina. To advance in the characterizationof pSmeLPU88b plasmid, the full sequence was obtained. pSmeLPU88b is 35.9 kbin size, had an average GC%of 58.6 and 31 CDS. Two replication modules were identifiedin silico: one belonging to the repABC type, and the other to the repC. The replication modulespresented high DNA identity to the replication modules from plasmid pMBA9a presentin an S. meliloti isolate from Canada. In addition, three CDS presenting identity with recombinasesand with toxin-antitoxin systems were found downstream of the repABC system. Itis noteworthy that these CDS present the same genetic structure in pSmeLPU88b and inother rhizobial plasmids. Moreover, in all cases they are found downstream of the repABCoperon. By cloning each replication system in suicide plasmids, we demonstrated that eachof them can support plasmid replication in the S. meliloti genetic background, but with differentstability behavior. Interestingly, while incompatibility analysis of the cloned rep systemsresults in the loss of the parental module, both obtained plasmids can coexist together.