Disparate origins of Bradyrhizobium symbionts for invasive populations of Cytisus scoparius (Leguminosae) in North America.
To identify the geographic origin of nodule bacteria associated with invasion of the European legume Cytisus scoparius in the United States, isolates from 15 sites in six states were compared to > 200 Bradyrhizobium strains from indigenous legumes in the U.S., Mexico, Europe (six countries), Morocco, and Australia. Portions of five housekeeping loci (2849 bp) were sequenced, along with the nifD locus in the symbiosis island (SI) portion of the Bradyrhizobium chromosome. Bayesian phylogenetic analysis showed that North American C. scoparius symbionts had highly heterogeneous ancestry. Some were grouped into three distinct clades of European C. scoparius symbionts. One isolate had both housekeeping and SI genes belonging to a Bradyrhizobium clade from native legumes in western North America. Two other clades had mosaic ancestry: sequences for nifD as well as two other SI genes (nifH, nodC) were highly similar or identical to a C. scoparius strain from Spain, while their housekeeping loci belonged to American Bradyrhizobium clades. Thus, it appears that bacteria ancestrally associated with other North American legumes have evolved to utilize C. scoparius, by acquiring SI-region genes from European C. scoparius symbionts. Inoculation assays indicated that North American isolates were as competent as European strains in promoting plant growth, consistent with the findings on symbiont ancestry.
Department of Biological Sciences, State University of New York, Binghamton, NY, USA.
Kevin
K
Horn
Ingrid M
IM
Parker
Wanda
W
Malek
Susana
S
Rodríguez-Echeverría
Matthew A
MA
Parker
D001483:Base Sequence; D001499:Bayes Theorem; D020369:Bradyrhizobium / Q000145:classification / Q000235:genetics*; D029865:Cytisus / Q000382:microbiology*; D005060:Europe; D005798:Genes, Bacterial; D020043:Genes, Essential; D044404:Genomic Islands; D058865:Introduced Species; D058885:Multilocus Sequence Typing; D010641:Phenotype; D010802:Phylogeny; D058974:Phylogeography; D012335:RNA, Ribosomal / Q000235:genetics; D013559:Symbiosis / Q000235:genetics; D014481:United States
D012335:RNA, Ribosomal
biologic invasions; horizontal gene transfer; microbial biogeography; mutualism; nitrogen fixation symbiosis; phylogeography