Legume symbiotic nitrogen fixation by beta-proteobacteria is widespread in nature.
Following the initial discovery of two legume-nodulating Burkholderia strains (L. Moulin, A. Munive, B. Dreyfus, and C. Boivin-Masson, Nature 411:948-950, 2001), we identified as nitrogen-fixing legume symbionts at least 50 different strains of Burkholderia caribensis and Ralstonia taiwanensis, all belonging to the beta-subclass of proteobacteria, thus extending the phylogenetic diversity of the rhizobia. R. taiwanensis was found to represent 93% of the Mimosa isolates in Taiwan, indicating that beta-proteobacteria can be the specific symbionts of a legume. The nod genes of rhizobial beta-proteobacteria (beta-rhizobia) are very similar to those of rhizobia from the alpha-subclass (alpha-rhizobia), strongly supporting the hypothesis of the unique origin of common nod genes. The beta-rhizobial nod genes are located on a 0.5-Mb plasmid, together with the nifH gene, in R. taiwanensis and Burkholderia phymatum. Phylogenetic analysis of available nodA gene sequences clustered beta-rhizobial sequences in two nodA lineages intertwined with alpha-rhizobial sequences. On the other hand, the beta-rhizobia were grouped with free-living nitrogen-fixing beta-proteobacteria on the basis of the nifH phylogenetic tree. These findings suggest that beta-rhizobia evolved from diazotrophs through multiple lateral nod gene transfers.
Chen
Wen-Ming
WM
Laboratory of Microbiology, Department of Seafood Science, National Kaohsiung Institute of Marine Technology, Kaohsiung City 811, Taiwan.
Moulin
Lionel
L
Bontemps
Cyril
C
Vandamme
Peter
P
Béna
Gilles
G
Boivin-Masson
Catherine
C
D000217:Acyltransferases / Q000235:genetics; D000581:Amidohydrolases / Q000235:genetics; D001426:Bacterial Proteins; D019117:Burkholderia / Q000235:genetics*; D007887:Fabaceae / Q000382:microbiology; D022761:Gene Transfer, Horizontal / Q000235:genetics; D031298:Mimosa / Q000382:microbiology; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D043367:Ralstonia / Q000235:genetics*; D013624:Taiwan
D001426:Bacterial Proteins; D010088:Oxidoreductases; C029130:nitrogenase reductase; D000217:Acyltransferases; C060770:NodA protein, Rhizobiales; D000581:Amidohydrolases; C417545:protein-deamidating enzyme, Chryseobacterium