|Van Berkum, Peter|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2011
Publication Date: 8/1/2011
Citation: Valverde, A., Velazquez, E., Cervantes, E., Igual, J.M., Van Berkum, P.B. 2011. Evidence for an American origin of the genes for symbiosis in R. lusitanum. Applied and Environmental Microbiology. 77(16):5665-5670. Interpretive Summary: Certain crops called legumes, important to North American agriculture, require bacteria to be associated with them in order to produce nitrogen for growth and production. Most of these crops originally came from other countries, one exception is common bean that came from the Americas. The common bean was introduced into Europe as a curiosity about 500 years ago, but now is an important crop both there and in the USA. In this work we wanted to find out whether beans growing in the Iberian Peninsula and the Americas were associated with the same bacterial species. We identified one species that was the same, but the other species has never been identified in American soils. The important finding is that this second bacterial species has acquired the genes necessary for the association with bean from two different American bacterial species. This would indicate that the genes for association with bean have been shared between bacterial species and that this sharing of genes has taken place in a very short period of time. Therefore, our results indicate that within the soils of agricultural fields, bacterial genes are easily and rapidly transferred between different species. This information will be valuable to companies who sell bacterial preparations for different leguminous crops. Also, geneticists, evolutionary biologists, microbiologists and environmental scientists will find this information useful in their studies to determine how these bacteria can interact with each other and with crop plants.
Technical Abstract: RAPD analysis was used to investigate the diversity of 179 bean isolates recovered from six field sites in the Arcos de Valdevez region of northwestern Portugal. The isolates were divided into 6 groups based on the fingerprint patterns that were obtained. Representatives for each group were selected for sequence analysis of 4 chromosomal DNA regions. Five of the groups were placed within Rhizobium lusitanum the other within R. tropici type IIA. Therefore, the collection of Portuguese bean isolates was shown to include the two species R. lusitanum and R. tropici. In plant tests the strain P1-7 of R. lusitanum nodulated and formed nitrogen-fixing symbioses both with Phaseolus vulgaris and Leucaena leucocephala. A methyltransferase encoding nodS gene identical with the R. tropici locus that confers wide host range was detected in the strain P1-7. Representatives of the other four R. lusitanum RAPD groups formed effective nitrogen-fixing symbioses with P. vulgaris, but no nodules were elicited with L. leucocephala. A methyltransferase encoding nodS gene also was detected in these four representatives, but in this case the locus was that identified with the narrow host-range R etli. Data from sequence analysis of nodC and nodS were comparable placing the R. lusitanum genes for symbiosis either within those of R. tropici or R. etli. These results would support the suggestion that R. lusitanum was the recipient of the genes for symbiosis with bean from both R. tropici and R. etli.