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Journal of Bacteriology, January 2001, p. 214-220, Vol. 183, No. 1
LSTM, UMR 113 IRD/INRA/AGRO-M/CIRAD,
34398 Montpellier Cedex 5, France,1 and
Laboratorium voor Microbiologie, Universiteit Gent, B-9000,
Ghent, Belgium2
Received 30 June 2000/Accepted 3 October 2000
Rhizobia described so far belong to three distinct phylogenetic
branches within the
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.214-220.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Methylotrophic Methylobacterium
Bacteria Nodulate and Fix Nitrogen in Symbiosis with
Legumes
-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
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.
*
Corresponding author. Mailing address: LSTM, TA 10/J,
Baillarguet, 34398 Montpellier Cedex 5, France. Phone: (33) 467 593 824. Fax: (33) 467 593 802. E-mail:
Catherine.Boivin{at}mpl.ird.fr.
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