A new species of Devosia that forms a unique nitrogen-fixing root-nodule symbiosis with the aquatic legume Neptunia natans (L.f.) druce - PubMed (original) (raw)

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 et al. Appl Environ Microbiol. 2002 Nov.

Abstract

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.

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Figures

FIG. 1.

FIG. 1.

LMW RNA profiles of type species of fast-growing genera of bacteria from the family Rhizobiaceae that nodulate various legumes and of strains that nodulate N. natans: strain J1 (lane 1), strain J2 (lane 2), A. undicola LMG 11875T (lane 3), R. leguminosarum ATCC 10004T (lane 4), S. meliloti ATCC 3390T (lane 5), and M. loti ATCC 3669T (lane 6).

FIG. 2.

FIG. 2.

Comparative sequence analysis of 16S rDNA from strain J1 and representative related strains from GenBank. The significance of each branch is indicated by a bootstrap value calculated for 1,000 subsets. Bar, 4 nt substitutions per 100 nt.

FIG. 3.

FIG. 3.

Comparative sequence analysis of nodD gene sequences from strain J1 and representative related strains from GenBank. The significance of each branch is indicated by a bootstrap value calculated for 1,000 subsets. Bar, 5 nt substitutions per 100 nt.

FIG. 4.

FIG. 4.

Comparative sequence analysis of nifH gene sequences from strain J1 and representative related strains from GenBank. The significance of each branch is indicated by a bootstrap value calculated for 1,000 subsets. Bar, 5 nt substitutions per 100 nt.

FIG. 5.

FIG. 5.

(A) Plasmid profile in horizontal 0.7% agarose gel. Lanes: 1, D. riboflavina LMG2277T; 2, strain J1; 3, strain J2; MW, S. meliloti GR4. (B) Southern blot hybridization with the digoxigenin-labeled nodD probe. Lanes: 4, D. riboflavina LMG2277T; 5, strain J1; 6, strain J2. (C) Southern blot hybridization with the digoxigenin-labeled nifH probe. Lanes: 7, D. riboflavina LMG2277T; 8, strain J1; 9, strain J2.

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