Genetic diversity of rhizobia isolated from legume species nodules in the temperate forests of Mexico

Santoyo-Páez Yuriria 2, Trujeque.Montiel Claudia 3, Contreras-Jiménez José-Luis 4, Villegas Maria del Carmen 2, Munive José-Antonio 3, Munive José-Antonio 1

1 Benemérita Universidad Autónoma de Puebla Microbiology Edif 76, 3er Piso, Instituto de Ciencias, CU, 72570 Puebla Puebla Mexico
2 Centro de Investigación en Biotecnología Aplicada, CIBA-IPN, Tlaxcala, México.
3 Laboratorio de Microbiología del Suelo, Centro de Investigaciones en Ciencias Microbiológicas,
4 Herbario - Jardín Botánico, Benemérita Universidad Autónoma de Puebla, México.

In Mexico, forests used to cover a very important proportion of the country, but deforestation, which has been increasing year after year, has almost destroyed all of them. These forests are characterised by a high diversity of plants, with a high proportion of trees belonging to the Leguminoseae family. A main advantage of members of this family is their ability to establish a symbiotic interaction with nitrogen-fixing soil bacteria collectively named rhizobia. Inside the leguminous species in the forest of Mexico, we found a great diversity, from shrubs to trees, but not all species presented nodulation. Only 60% of species were nodulated. We stablished a collection of 138 strains, from which, 51 have been tested for nodulation and nitrogen fixation. Most of them (90%) were capables of nodulating Macroptillium atropurpureum plants. From these bacteria, 53% were nitrogen fixing strains, as showed by the ARA method. The ARA assays showed that 28% of strains have a high nitrogen fixation potential. Inside these bacteria, we found a great biodiversity, showed by their carbon source utilization and ERIC-PCR patterns. We also decided to identify and to characterise the rhizobia isolated from these temperate forest leguminous species by sequencing the 16S rDNA and nodC genes. 16S rDNA sequencing analisis showed a most important presence of bacteria belonging to genus Bradyrhizobium inside these forest species. A number of irhizobia strains with a great capability for increasing the development of leguminous trees have been isolated. The most efficient strains for nodulation and nitrogen fixation will be chosen for a nursery nodulation essay, to make a collection of the best strains useful as inoculum in forestry for the restoration of disturbed forests.

Key words: Legume, Symbioses, Nodulation, Rhizobia, Nitrogen Fixation