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Applied and Environmental Microbiology, November 2002, p. 5217-5222, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5217-5222.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

A New Species of Devosia That Forms a Unique Nitrogen-Fixing Root-Nodule Symbiosis with the Aquatic Legume Neptunia natans (L.f.) Druce

Raul Rivas,1 Encarna Velázquez,1* Anne Willems,2 Nieves Vizcaíno,1 Nanjappa S. Subba-Rao,3 Pedro F. Mateos,1 Monique Gillis,2 Frank B. Dazzo,3 and Eustoquio Martínez-Molina1

Departamento de Microbiología y Genética, Centro Hispano-Luso de Investigaciones Agrarias, Universidad de Salamanca, Spain,1 Laboratorium voor Microbiologie, Vakgroep Biochemie, Fysiologie en Microbiologie, Ghent, Belgium,2 Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan3

Received 18 March 2002/ Accepted 7 August 2002

Rhizobia are the common bacterial symbionts that form nitrogen-fixing root nodules in legumes. However, recently other bacteria have been shown to nodulate and fix nitrogen symbiotically with these plants. Neptunia natans is an aquatic legume indigenous to tropical and subtropical regions and in African soils is nodulated by Allorhizobium undicola. This legume develops an unusual root-nodule symbiosis on floating stems in aquatic environments through a unique infection process. Here, we analyzed the low-molecular-weight RNA and 16S ribosomal DNA (rDNA) sequence of the same fast-growing isolates from India that were previously used to define the developmental morphology of the unique infection process in this symbiosis with N. natans and found that they are phylogenetically located in the genus Devosia, not Allorhizobium or Rhizobium. The 16S rDNA sequences of these two Neptunia-nodulating Devosia strains differ from the only species currently described in that genus, Devosia riboflavina. From the same isolated colonies, we also located their nodD and nifH genes involved in nodulation and nitrogen fixation on a plasmid of approximately 170 kb. Sequence analysis showed that their nodD and nifH genes are most closely related to nodD and nifH of Rhizobium tropici, suggesting that this newly described Neptunia-nodulating Devosia species may have acquired these symbiotic genes by horizontal transfer.

* Corresponding author. Mailing address: Departamento de Microbiología y Genética, Lab. 209, Edificio Departamental de Biología, Campus M. Unamuno, 37007 Salamanca, Spain. Phone: 34 923 294532. Fax: 34 923 224876. E-mail: evp{at}usal.es.

Applied and Environmental Microbiology, November 2002, p. 5217-5222, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5217-5222.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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Copyright © 2002 by the American Society for Microbiology. All rights reserved.