|Van Berkum, Peter|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2001
Publication Date: N/A
Interpretive Summary: Globally, soybean is the most important grain legume. Because soybean is a legume, it benefits from biological nitrogen fixation through a symbiosis with soil bacteria of two different genera. In agriculture, the benefit is in the form of enhanced efficiency of crop production. Management of biological nitrogen fixation involves the inoculation of the appropriate bacterial cultures at the time of sowing. These bacterial cultures are available to the farmer as inoculants manufactured in industry. The problem is that many different bacteria are available, but comprehensive investigations for evolutionary differences have not been done. Here we report that a seemingly unrelated aquatic bacterial species isolated from lakewater in Germany is a legume symbiont that is very closely related to the symbionts of soybean. We discovered this by study of the genetic relationships of the genus that include the soybean symbionts. We concluded that the study of genetic relationships among bacteria is important to develop an understanding of the soybean symbiosis, how it evolved, how it functions, what potential genetic opportunities may be available for its improvement. Our results will be useful to scientists who are interested in evolutionary biology, taxonomy and strain identification, and the soybean symbiosis.
Technical Abstract: Blastobacter are fresh water bacteria that form rosette structures by cellular attachment to a common base. Comparative analyses of ribosomal 16S rRNA gene and Internally Transcribed Spacer (ITS) region sequences indicated that Bl. denitrificans is a member of the alpha-subdivision of Proteobacteria. Among the alpha-Proteobacteria, Bl. 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 Bl. 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 Bl. 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 the value of molecular phylogenetic analyses for predicting ecological behavior.