Symbiosis within Symbiosis: Evolving Nitrogen-Fixing Legume Symbionts

• Published in: Trends in microbiology (Regular ed.) Vol. 24; no. 1; pp. 63 - 75
• Main Authors: Remigi, Philippe, Zhu, Jun, Young, J. Peter W, Masson-Boivin, Catherine
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2016; Elsevier
• Subjects: Alphaproteobacteria - genetics; Alphaproteobacteria - physiology; Biological Evolution; evolution; Evolution, Molecular; Fabaceae - genetics; Fabaceae - microbiology; Fabaceae - physiology; Genes, Bacterial; horizontal gene transfer; host adaptation; Internal Medicine; Life Sciences; Nitrogen - metabolism; Nitrogen Fixation - physiology; Phylogeny; Rhizobium; Rhizobium - genetics; Rhizobium - physiology; Soil Microbiology; symbiosis; Symbiosis - genetics; Symbiosis - physiology; Vegetal Biology; host adaptation; Rhizobium; evolution; horizontal gene transfer; symbiosis; SEQUENCE-ANALYSIS; SINORHIZOBIUM-MELILOTI; MESORHIZOBIUM-LOTI; COMPARATIVE GENOMICS; EXPERIMENTAL EVOLUTION; BACTERIAL SYMBIOSIS; NODULATING STRAINS; ESCHERICHIA-COLI; RHIZOBIUM MUTUALISM; ALPHA-PROTEOBACTERIA
• ISSN: 0966-842X; 1878-4380
• DOI: 10.1016/j.tim.2015.10.007

Bacterial accessory genes are genomic symbionts with an evolutionary history and future that is different from that of their hosts. Packages of accessory genes move from strain to strain and confer important adaptations, such as interaction with eukaryotes. The ability to fix nitrogen with legumes is a remarkable example of a complex trait spread by horizontal transfer of a few key symbiotic genes, converting soil bacteria into legume symbionts. Rhizobia belong to hundreds of species restricted to a dozen genera of the Alphaproteobacteria and Betaproteobacteria, suggesting infrequent successful transfer between genera but frequent successful transfer within genera. Here we review the genetic and environmental conditions and selective forces that have shaped evolution of this complex symbiotic trait.