Methylotrophic Methylobacterium bacteria nodulate and fix nitrogen in symbiosis with legumes

Sy Abdourahmane, Giraud Eric, Jourand Philippe, Garcia Nelly, Willems Anne, De Lajudie Philippe, Prin Yves, Neyra Marc, Gillis Monique, Boivin-Masson Catherine, Dreyfus Bernard. 2001. Methylotrophic Methylobacterium bacteria nodulate and fix nitrogen in symbiosis with legumes. Journal of Bacteriology, 183 (1) : 214-220.

https://doi.org/10.1128/JB.183.1.214-220.2001

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Résumé : 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.

Mots-clés Agrovoc : Crotalaria, phylogénie, adn, symbiose, Fixation de l'azote

Mots-clés complémentaires : Activité protéolytique

Classification Agris : P34 - Biologie du sol

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