IBBM   21076
INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
artículos
Título:
Conjugal properties of the Sinorhozobium meliloti plasmid mobilome
Autor/es:
PISTORIO, M. J.; GIUSTI, M. A; DEL PAPA, M. F.,; TORRES TEJERIZO, G; DRAGHI, W. O.; LOZANO, M.J.; A. LAGARES
Revista:
FEMS MICROBIOLOGY ECOLOGY
Editorial:
Blackwell Publishing
Referencias:
Año: 2008 vol. 63 p. 372 - 382
ISSN:
0168-6496
Resumen:
The biology and biochemistry of plasmid transfer in soil bacteria is currently under active investigation because of its central role in prokaryote adaptation and evolution. In this work, we examined the conjugal properties of the cryptic plasmids present in a collection of the N2-fixing legume-symbiont Sinorhizobium meliloti in order to investigate how frequently conjugative/mobilizable plasmids are found within the diversity of the population, and the degree of cross-complementation among the helper functions. The study was performed on 65 S. meliloti isolates, which were grouped into 22 plasmid-profile types (i.e., plasmid OTUs-Operational Taxonomic Units). The cumulative Shannon index calculated for the observed plasmid profiles showed a clear saturation plateau for n>49 (n = number of isolates used for the calculation), thus indicating an adequate representation of the population plasmid-profile types in the isolates studied. The results show that isolates of nearly 14% of the plasmid OTUs hosted transmissible plasmids and that isolates of 29% of the plasmid OTUs were able to retransfer the previously characterized mobilizable-cryptic plasmid pSmeLPU88b (Pistorio et al., 2003) to a third recipient strain. The proportion of rhizobia carrying transmissible replicons was inferred from experiments in the laboratory. It is noteworthy that isolates belonging to 14% of the plasmid OTUs proved to be refractory to the entrance of the model plasmid pSmeLPU88b, suggesting either the presence of surface exclusion phenomena or the occurrence of restriction incompatibility with the incoming replicon. Incompatibility for replication between resident plasmids and plasmid pSmeLPU88b was observed in ca. 20% of the OTUs. The results reported here reveal a widespread compatibility among the conjugal functions of the cryptic plasmids in S. meliloti, and this fact together with the observed high proportion of existing donor genotypes point to the extrachromosomal compartment of the species as being an extremely active plasmid mobilome.