Methylotrophic Methylobacterium bacteria nodulate and fix nitrogen in symbiosis with legumes.
Rhizobia described so far belong to three distinct phylogenetic branches within the alpha-2 subclass of Proteobacteria. Here we report the discovery of a fourth rhizobial branch involving bacteria of the Methylobacterium genus. Rhizobia isolated from Crotalaria legumes were assigned to a new species, "Methylobacterium nodulans," within the Methylobacterium genus on the basis of 16S ribosomal DNA analyses. We demonstrated that these rhizobia facultatively grow on methanol, which is a characteristic of Methylobacterium spp. but a unique feature among rhizobia. Genes encoding two key enzymes of methylotrophy and nodulation, the mxaF gene, encoding the alpha subunit of the methanol dehydrogenase, and the nodA gene, encoding an acyltransferase involved in Nod factor biosynthesis, were sequenced for the type strain, ORS2060. Plant tests and nodA amplification assays showed that "M. nodulans" is the only nodulating Methylobacterium sp. identified so far. Phylogenetic sequence analysis showed that "M. nodulans" NodA is closely related to Bradyrhizobium NodA, suggesting that this gene was acquired by horizontal gene transfer.
Sy
A
A
LSTM, UMR 113 IRD/INRA/AGRO-M/CIRAD, 34398 Montpellier Cedex 5, France.
Giraud
E
E
Jourand
P
P
Garcia
N
N
Willems
A
A
de Lajudie
P
P
Prin
Y
Y
Neyra
M
M
Gillis
M
M
Boivin-Masson
C
C
Dreyfus
B
B
D000217:Acyltransferases / Q000235:genetics; D000429:Alcohol Oxidoreductases / Q000235:genetics; D001426:Bacterial Proteins; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D004275:DNA, Ribosomal / Q000032:analysis / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology*; D000432:Methanol / Q000378:metabolism*; D020580:Methylobacterium / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000502:physiology*; D010084:Oxidation-Reduction; D010802:Phylogeny; D010946:Plants, Medicinal; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013559:Symbiosis
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S; D000429:Alcohol Oxidoreductases; C019641:alcohol dehydrogenase (acceptor); D000217:Acyltransferases; C060770:NodA protein, Rhizobiales; D000432:Methanol