Genetic diversity and host range of rhizobia nodulating Lotus tenuis in typical soils of the Salado River Basin (Argentina).

MARÍA JULIA ESTRELLA, SOCORRO MUÑOZ, MARÍA JOSÉ SOTO, OSCAR A. RUIZ & JUAN SANJUÁN

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

AMER SOC MICROBIOLOGY

Año: 2009 vol. 75 p. 1088 - 1098

0099-2240

One hundred and three root nodule isolates were used to estimate the diversity among bacteria nodulating L. tenuis in typical soils of the Salado River Basin. A high level of genetic diversity was revealed by REP-PCR and seventy seven isolates with unique genomic fingerprints could be further differentiated into two clusters, A and B after 16S rDNA RFLP analysis. Cluster A strains appeared related to genus Mesorhizobium whereas cluster B was related to Rhizobium. 16S sequence and phylogenetic analysis further supported the distribution of symbiotic isolates within either Rhizobium or Mesorhizobium, except isolate BA135 whose 16S rRNA gene was closely related to genus Aminobacter. Most Mesorhizobium-like isolates were closely related to M. amorphae, M. mediterraneum, M. tianshanense or to the broad host-range strain NZP2037, but surprisingly few isolates grouped with the M. loti type strain NZP2213. Rhizobium-like strains were related to R. gallicum, R. etli or R. tropici, which have Phaseolus vulgaris as a common host. However no nodC or nifH genes could be amplified from the L. tenuis isolates, suggesting they carry rather divergent symbiotic genes. On the contrary, nodC genes from the Mesorhizobium and Aminobacter strains were closely related to nodC from narrow host-range M.loti strains. Likewise, nifH gene sequences were very conserved among the Argentinian isolates and reference Lotus rhizobia. The high conservation of nodC and nifH genes suggest a common origin of symbiotic genes among narrow host-range Lotus symbionts, supporting both intra- andintergeneric horizontal gene transfer as an important mechanism for the spread of the symbiotic capacity in the Salado River Basin.One hundred and three root nodule isolates were used to estimate the diversity among bacteria nodulating L. tenuis in typical soils of the Salado River Basin. A high level of genetic diversity was revealed by REP-PCR and seventy seven isolates with unique genomic fingerprints could be further differentiated into two clusters, A and B after 16S rDNA RFLP analysis. Cluster A strains appeared related to genus Mesorhizobium whereas cluster B was related to Rhizobium. 16S sequence and phylogenetic analysis further supported the distribution of symbiotic isolates within either Rhizobium or Mesorhizobium, except isolate BA135 whose 16S rRNA gene was closely related to genus Aminobacter. Most Mesorhizobium-like isolates were closely related to M. amorphae, M. mediterraneum, M. tianshanense or to the broad host-range strain NZP2037, but surprisingly few isolates grouped with the M. loti type strain NZP2213. Rhizobium-like strains were related to R. gallicum, R. etli or R. tropici, which have Phaseolus vulgaris as a common host. However no nodC or nifH genes could be amplified from the L. tenuis isolates, suggesting they carry rather divergent symbiotic genes. On the contrary, nodC genes from the Mesorhizobium and Aminobacter strains were closely related to nodC from narrow host-range M.loti strains. Likewise, nifH gene sequences were very conserved among the Argentinian isolates and reference Lotus rhizobia. The high conservation of nodC and nifH genes suggest a common origin of symbiotic genes among narrow host-range Lotus symbionts, supporting both intra- andintergeneric horizontal gene transfer as an important mechanism for the spread of the symbiotic capacity in the Salado River Basin.