A population of twelve acid tolerant alfalfa nodulating Rhizobium strains isolated from different sites in Argentina exhibit the same molecular characteristics as the Rhizobium spp strain Or 191

WEGENER, C.; SCHRÖDER, S.; KAPP, D.; PÜHLER, A.; SEGUNDO LOPEZ, E.; MARTINEZ - ABARCA, F.; TORO, N.; DEL PAPA, M.F.; BALAGUÉ, L.J.; LAGARES, A.; MARTINEZ-DRETS, G.; NIEHAUS, K.

SYMBIOSIS

SPRINGER

Lugar: Berlin; Año: 2001 vol. 30 p. 141 - 162

0334-5114

Alfalfa-nodulating rhizobia from acidic soils (pH 5.52-6.2) in Argentina comprise a distinct group of acid-tolerant Rhizobium isolates which were found to be related to Rhizobium sp. strain Or 191 (Del Papa et al., 1999). Lipopolysaccharide profiles and 16S rDNA sequences demonstrated that all twelve acidtolerant Rhizobium isolates belonged to one species. Furthermore, the group of acid tolerant Rhizobium isolates was formed by one strain type, since they gave the same plasmid profile as well as the same IS- and ERIC-fingerprints. All acid-tolerant Rhizobium isolates were genetically identical even though they were isolated at very different locations in Argentina. The isolates nodulated a range of Medicago, Melilotus and Trigonella species, and Phaseolus vulgaris, but were weak in nitrogen fixation. M. sativa nodules induced by one of the acid-tolerant rhizobial isolates contained several bacteroids within a vesicle-like structure, in contrast to nodules induced by the reference strain S. meliloti 2011. Reisolation of bacteria from root nodules resulted in approx. 40 times more colony forming bacteria in case of the acid-tolerant strains. These strains mark the borderline between a symbiotic and a parasitic plant-microbe interaction.