INVESTIGADORES
DRAGHI Walter Omar
artículos
Título:
Genetic and functional characterization of a yet-unclassified rhizobial Dtr (DNA-transfer-and-replication) region from a ubiquitous plasmid conjugal system present in Sinorhizobium meliloti, in Sinorhizobium medicae, and in other nonrhizobial Gram-negativ
Autor/es:
GIUSTI, M.A.; PISTORIO, M.; LOZANO, M.J.; TORRES TEJERIZO, G.A.; SALAS, M.E.; MARTINI, C.; LÓPEZ, J.L.; DRAGHI, W.O.; DEL PAPA, M.F.; PÉREZ MENDOZA, D.; SAN JUAN, J.; LAGARES, A.
Revista:
PLASMID.
Editorial:
ACADEMIC PRESS INC ELSEVIER SCIENCE
Referencias:
Lugar: Amsterdam; Año: 2012 vol. 67 p. 199 - 210
ISSN:
0147-619X
Resumen:
Rhizobia are Gram-negative bacteria that live in soils and associate
with leguminous plants to establish nitrogen-fixing symbioses. The
ability of these bacteria to undergo horizontal gene transfer (HGT) is
thought to be one of the main features to explain both the origin of
their symbiotic life-style and the plasticity and dynamics of their
genomes. In our laboratory we have previously characterized at the
species level the non-pSym plasmid mobilome in Sinorhizobium meliloti,
the symbiont of Medicago spp., and have found a high incidence of
conjugal activity in many plasmids (Pistorio et al., 2008). In this work
we characterized the Dtr (DNA-transfer-and-replication) region of one
of those plasmids, pSmeLPU88b. This mobilization region was found to
represent a previously unclassified Dtr type in rhizobia (hereafter
type-IV), highly ubiquitous in S. meliloti and found in other genera of
Gram-negative bacteria as well; including Agrobacterium, Ochrobactrum,
and Chelativorans. The oriT of the type-IV Dtr described here could be
located by function within a DNA fragment of 278 bp, between the
divergent genes parA and mobC. The phylogenetic analysis of the cognate
relaxase MobZ indicated that this protein groups close to the previously
defined MOB(P3) and MOB(P4) type of enzymes, but is located in a
separate and novel cluster that we have designated MOB(P0). Noteworthy,
MOB(P0) and MOB(P4) relaxases were frequently associated with plasmids
present in rhizospheric soil bacteria. A comparison of the nod-gene
locations with the phylogenetic topology of the rhizobial relaxases
revealed that the symbiotic genes are found on diverse plasmids bearing
any of the four Dtr types, thus indicating that pSym plasmids are not
specifically associated with any particular mobilization system.
Finally, we demonstrated that the type-IV Dtr promoted the mobilization
of plasmids from S. meliloti to Sinorhizobium medicae as well as from
these rhizobia to other bacteria by means of their own helper functions.
The results present an as-yet-unclassified and seemingly ubiquitous
conjugal system that provides a mechanistic support for the HGT between
sympatric rhizobia of Medicago roots, and between other soil and
rhizospheric bacteria.