INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
congresos y reuniones científicas
Genome sequencing of the broad-host-range Rhizobium sp. LPU83 and characterization of its chromosomal phylogenetic relationships
TORRES TEJERIZO, G.A.; DEL PAPA, M.F.; LOZANO, M.; GIUSTI, M. A.; MARTINI, C.; SALAS, M.E.; SALTO, I.; LAGARES, A.; PISTORIO, M.
Congreso; VII Congreso Argentino de Microbiología General, SAMIGE Del Bicentenario; 2011
Alfalfa (Medicago sativa) is the most widely cultivated forage legume for cattle and animal feeding over the world. In Argentina, over 6 million hectares of land are cultivated with alfalfa, where the productive symbiosis with N2-fixation efficient rhizobia represents a crucial condition for insuring the entry of fixed atmospheric nitrogen into agricultural soils (1). A distinctive feature of alfalfa is the marked specificity of this legume towards its microsymbiont partners E. meliloti or E. medicae, but a different population of rhizobia represented by the strains Rhizobium sp. Or191 and LPU83 are present in fields and are able to nodulate alfalfa (2, 3). These rhizobia are acid-tolerant and have an extended host range; moreover, they possess the ability to nodulate Phaseolus vulgaris (3) and Leucaena leucocephala (2), among other legumes, and are highly competitive for the nodulation of alfalfa in acid soils. A phylogenetic analysis of the 16s rRNA gene showed that the Oregon-like strains were related to the bean-, pea-, and clover-nodulating rhizobia. In contrast, the phylogenetic analysis of the nodC gene indicated that the E. meliloti nodC gene, is the most closely related one, thus suggesting that both nodC genes originated from a common ancestor. Moreover, the collected genetic information has revealed that the genomic structure of these rhizobial isolates is complex in terms of sequence similarities shared with other rhizobia. Such a "patched" genetic composition has obviously imposed severe restrictions to the classical taxonomy of these rhizobia. In order to more completely characterize the genetics of the Oregon-like strains, Rhizobium sp. LPU83 was fully sequenced. The draft nucleotide sequence of this strain was established by a de novo sequencing approach carried out on a GS FLX system (454 Life Sciences, Roche) using the Titanium sequencing chemistry. An in-depth phylogenetic study was performed involving concatenation of these seven genes (dnaK, glnA, gltA, gyrB, recA, rpoB, and thrC). The LPU83 strain is located close to a clade where Rhizobium etli and Rhizobium leguminosarum were situated, as had been observed previously for other housekeeping genes. Interestingly, in this tree LPU83 appears to be a precursor of this linage. The complete LPU83 genomic sequence together with future information from new, likewise entirely sequenced rhizobial genomes will constitute key information towards a more complete characterization and reconstruction of the Oregon-like genomic genealogy. 1. A. Perticari et al., Divulgación Técnica del Instituto de Microbiología Agrícola.CICA-INTA, Castelar, Argentina, (1989). 2. M. F. Del Papa et al., Appl Environ Microbiol 65, 1420 (Apr, 1999). 3. B. D. Eardly, D. B. Hannaway, P. J. Bottomley, Appl Environ Microbiol 50, 1422 (Dec, 1985).