Horizontal Gene Transfer and Homologous Recombination Drive the Evolution of the Nitrogen-Fixing Symbionts of Medicago Species
- 15 July 2007
- journal article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 189 (14), 5223-5236
- https://doi.org/10.1128/jb.00105-07
Abstract
Using nitrogen-fixing Sinorhizobium species that interact with Medicago plants as a model system, we aimed at clarifying how sex has shaped the diversity of bacteria associated with the genus Medicago on the interspecific and intraspecific scales. To gain insights into the diversification of these symbionts, we inferred a topology that includes the different specificity groups which interact with Medicago species, based on sequences of the nodulation gene cluster. Furthermore, 126 bacterial isolates were obtained from two soil samples, using Medicago truncatula and Medicago laciniata as host plants, to study the differentiation between populations of Sinorhizobium medicae , Sinorhizobium meliloti bv. meliloti, and S. meliloti bv. medicaginis. The former two can be associated with M. truncatula (among other species of Medicago ), whereas the last organism is the specific symbiont of M. laciniata . These bacteria were characterized using a multilocus sequence analysis of four loci, located on the chromosome and on the two megaplasmids of S. meliloti. The phylogenetic results reveal that several interspecific horizontal gene transfers occurred during the diversification of Medicago symbionts. Within S. meliloti , the analyses show that nod genes specific to different host plants have spread to different genetic backgrounds through homologous recombination, preventing further divergence of the different ecotypes. Thus, specialization to different host plant species does not prevent the occurrence of gene flow among host-specific biovars of S. meliloti , whereas reproductive isolation between S. meliloti bv. meliloti and S. medicae is maintained even though these bacteria can cooccur in sympatry on the same individual host plants.Keywords
This publication has 56 references indexed in Scilit:
- Recombination and the Nature of Bacterial SpeciationScience, 2007
- Multilocus Sequence Typing as an Approach for Population Analysis of Medicago -Nodulating RhizobiaJournal of Bacteriology, 2006
- Horizontal gene transfer: perspectives at a crossroads of scientific disciplinesNature Reviews Microbiology, 2005
- RDP2: recombination detection and analysis from sequence alignmentsBioinformatics, 2004
- DnaSP, DNA polymorphism analyses by the coalescent and other methodsBioinformatics, 2003
- A Phylogenomic Approach to Bacterial Phylogeny: Evidence of a Core of Genes Sharing a Common HistoryGenome Research, 2002
- Multiple Comparisons of Log-Likelihoods with Applications to Phylogenetic InferenceMolecular Biology and Evolution, 1999
- How clonal are bacteria?Proceedings of the National Academy of Sciences of the United States of America, 1993
- Cooperative Action of Rhizobium meliloti Nodulation and Infection Mutants during the Process of Forming Mixed Infected Alfalfa Nodules.THE PLANT CELL ONLINE, 1990
- A Manual for the Practical Study of Root-Nodule Bacteria.Journal of Applied Ecology, 1971