Résumé
Data on 72 non-pigmented bacterial strains that specifically induce nitrogen-fixing root nodules on the legume species Crotalaria glaucoides, Crotalaria perrottetii and Crotalaria podocarpa are reviewed. By SDS-PAGE analysis of total protein patterns and by 16S rRNA PCR-RFLP, these strains form a homogeneous group that is separate from other legume root-nodule-forming bacteria. The 16S rRNA gene-based phylogeny indicates that these bacteria belong to the genus Methylobacterium. They can grow on C(1) compounds such as methanol, formate and formaldehyde but not methylamine as sole carbon source, and carry an mxaF gene, encoding methanol dehydrogenase, which supports their methylotrophic metabolism. Presence of a nodA nodulation gene, and ability to nodulate plants of Crotalaria species and to fix nitrogen are features that separate the strains currently included in this group from other members of the genus Methylobacterium. The present study includes additional genotypic and phenotypic characterization of this novel Methylobacterium species, i.e. nifH gene sequence, morphology, physiology, enzymic and carbon source assimilation tests and antibiotic resistance. The name Methylobacterium nodulans sp. nov. (type strain, ORS 2060(T)=CNCM I 2342(T)=LMG 21967(T)) is proposed for this group of root-nodule-forming bacteria.