Population genomics of the symbiotic plasmids of sympatric nitrogen-fixing Rhizobium species associated with Phaseolus vulgaris.
Cultivated common beans are the primary protein source for millions of people around the world who subsist on low-input agriculture, enabled by the symbiotic N2 -fixation these legumes perform in association with rhizobia. Within a single agricultural plot, multiple Rhizobium species can nodulate bean roots, but it is unclear how genetically isolated these species remain in sympatry. To better understand this issue, we sequenced and compared the genomes of 33 strains isolated from the rhizosphere and root nodules of a particular bean variety grown in the same agricultural plot. We found that the Rhizobium species we observed coexist with low genetic recombination across their core genomes. Accessory plasmids thought to be necessary for the saprophytic lifestyle in soil show similar levels of genetic isolation, but with higher rates of recombination than the chromosomes. However, the symbiotic plasmids are extremely similar, with high rates of recombination and do not appear to have co-evolved with the chromosome or accessory plasmids. Therefore, while Rhizobium species are genetically isolated units within the microbial community, a common symbiotic plasmid allows all Rhizobium species to engage in symbiosis with the same host in a single agricultural plot.
Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México.
Olga M
OM
Pérez Carrascal
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
David
D
VanInsberghe
Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México.
Soledad
S
Juárez
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
Martin F
MF
Polz
Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México.
Pablo
P
Vinuesa
Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México.
Víctor
V
González
D014644:Genetic Variation / Q000235:genetics; D058507:Host Specificity / Q000235:genetics*; D056186:Metagenomics; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics*; D027805:Phaseolus / Q000378:metabolism / Q000382:microbiology*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D010957:Plasmids / Q000235:genetics*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics; D012231:Rhizobium / Q000145:classification / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis / Q000235:genetics
D012336:RNA, Ribosomal, 16S; D009584:Nitrogen