The aquatic budding bacterium Blastobacter denitrificans is a nitrogen-fixing symbiont of Aeschynomene indica.
Blastobacter spp. are freshwater bacteria that form rosette structures by cellular attachment to a common base. Comparative analyses of ribosomal 16S rRNA gene and internally transcribed spacer region sequences indicated that B. denitrificans is a member of the alpha-subdivision of Proteobacteria. Among the alpha-Proteobacteria, B. denitrificans was related to a cluster of genera, including Rhodopseudomonas palustris, Afipia felis, Nitrobacter hamburgensis, and Bradyrhizobium spp. Although the precise phylogenetic relationships among these genera could not be established with a high degree of confidence, the sequences of B. denitrificans and several bradyrhizobial isolates from nodules of Aeschynomene indica were almost identical. Bradyrhizobia are bacteria that form nitrogen-fixing symbioses with legumes, including soybeans (Glycine max) and members of the genus Aeschynomene. From symbiotic infectiveness tests we demonstrated that the type strain for B. denitrificans, IFAM 1005, was capable of forming an effective nitrogen-fixing symbiosis with A. indica. Not only do these results reveal a previously unknown ecological adaptation of a relatively obscure aquatic bacterium, but they also demonstrate how evidence gathered from molecular systematic analyses can sometimes provide clues for predicting ecological behavior.
van Berkum
Peter
P
Soybean and Alfalfa Research Laboratory, Agricultural Research Service/USDA, HH-4, Bldg. 010, BARC-West, 10300 Baltimore Blvd., Beltsville, MD 20705, USA. pberkum@ba.ars.usda.gov
Eardly
Bertrand D
BD
D021903:DNA, Ribosomal Spacer / Q000235:genetics; D019143:Evolution, Molecular; D007887:Fabaceae / Q000382:microbiology*; D005618:Fresh Water / Q000382:microbiology*; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012230:Rhizobiaceae / Q000145:classification* / Q000235:genetics / Q000254:growth & development; D017422:Sequence Analysis, DNA; D013025:Glycine max / Q000382:microbiology; D013559:Symbiosis
D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S