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-negative bacteria

被引：23

作者：

de los Angeles Giusti, Maria ^{[1
]}

Pistorio, Mariano ^{[1
]}

Lozano, Mauricio J. ^{[1
]}

Torres Tejerizo, Gonzalo A. ^{[1
]}

Eugenia Salas, Maria ^{[1
]}

Carla Martini, Maria ^{[1
]}

Luis Lopez, Jose ^{[1
]}

Draghi, Walter O. ^{[1
]}

Florencia Del Papa, Maria ^{[1
]}

Perez-Mendoza, Daniel ^{[2
]}

Sanjuan, Juan ^{[2
]}

Lagares, Antonio ^{[1
]}

机构：

[1] Univ Nacl La Plata, Fac Ciencias Exactas, Dept Ciencias Biol, IBBM,CCT CONICET La Plata, RA-1900 La Plata, Buenos Aires, Argentina

[2] CSIC, Estn Expt Zaidin, Dept Microbiol Suelo & Sistemas Simbiot, Granada, Spain

来源：

PLASMID | 2012年 / 67卷 / 03期

关键词：

Relaxase; Cryptic plasmid; Conjugation machine; Rhizobia; LEGUMINOSARUM BV VICIAE; NITROGEN-FIXATION GENES; SYMBIOTIC PLASMID; AGROBACTERIUM-TUMEFACIENS; NODULATING STRAINS; INOCULANT STRAIN; LATERAL TRANSFER; SYM PLASMID; MOBILIZATION; IDENTIFICATION;

D O I：

10.1016/j.plasmid.2011.12.010

中图分类号：

Q3 [遗传学];

学科分类号：

071007 ; 090102 ;

摘要：

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 MOBP3 and MOBP4 type of enzymes, but is located in a separate and novel cluster that we have designated MOBP0. Noteworthy, MOBP0 and MOBP4 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. (C) 2012 Elsevier Inc. All rights reserved.

引用

页码：199 / 210

页数：12