Rhizobium tropici, a Novel Species Nodulating Phaseolus vulgaris L. Beans and Leucaena sp. Trees

Abstract

A new Rhizobium species that nodulates PhaseoZus vulgaris L. and Leucaena spp. is proposed on the basis of the results of multilocus enzyme electrophoresis, DNA-DNA hybridization, an analysis of ribosomal DNA organization, a sequence analysis of 16s rDNA, and an analysis of phenotypic characteristics. This taxon, Rhizobium tropici sp. nov., was previously named Rhizobium Zeguminosarum biovar phaseoli (type I1 strains) and was recognized by its host range (which includes Leucaena spp.) and nifgene organization. In contrast to R. Zeguminosarum biovar phaseoli, R. tropici strains tolerate high temperatures and high levels of acidity in culture and are symbiotically more stable. We identified two subgroups within R . tropici and describe them in this paper.Members of the genus Rhizobium nodulate the roots of leguminous plants. The rhizobia that infect peas, clovers, and beans (Phaseolus vulgaris L.) are clustered in a single species, Rhizobium leguminosarum (29), which has three biovars (Rhizobium leguminosarum biovar viciae, Rhizobium leguminosarum biovar trifolii, and Rhizobium leguminosarum biovar phaseoli); these biovars contain different symbiotic plasmids that encode distinct nodulation specificities. Nevertheless, heterogeneity in Rhizobium leguminosarum biovar phaseoli has been identified by using such different criteria as protein pattern (50), antibiotic resistance (2), serological type (49), multilocus enzyme electrophoresis behavior (45), DNA-DNA hybridization data (10, 26, 54), plasmid profile (37) , and exopolysaccharide structure (70).We previously distinguished two different types among isolates obtained from bean nodules and found differences in their symbiotic plasmids (36, 38, 39). Type I strains have multiple copies of nitrogenase n i m genes (39, 46), a narrow nodulation host range, and hybridize with the psi (polysaccharide inhibition) gene (3). Type I1 strains have single copies of nifgenes, nodulate Leucaena spp., and do not hybridize with the psi gene (36, 39).Type I1 strains have received attention because their symbiotic plasmids promote an effective and completely differentiated symbiotic process in Agrobacterium tumefaciens recipients (5, 38). They are genetically stable, retaining their symbiotic plasmid after prolonged incubation at 37°C. Some are heat tolerant (31) or acid and aluminum resistant (12, 25, 30, 62). The nodulation genes from one of these strains have been cloned (64). The chemical composition and structure of the extracellular polysaccharides from one type I1 strain differ from the chemical composition and structure of the extracellular polysaccharides from type I isolates (23).Type I1 strains have been less successful in competition for bean nodule occupancy than the type I strains used (41). The former have been reported to occur less frequently in * Corresponding author bean nodules (39). Nodule occupancy by type I1 strains can be enhanced under acid conditions (47, 63).To define the taxonomic position and the genetic relatedness of type I1 strains, we analyzed 64 typ...

Numerical Taxonomy of Rhizobium Strains from Legumes of the Temperate Zone

“…In recent years, progress towards the development of a more complete Rhizobium taxonomy has been made, and new species have been described: R. tropici (16), R. huakuii (3), and Rhizobium etli (25). Genomic relatedness between members of the family Rhizobiaceae has been revealed by modern approaches and has allowed the construction of phylogenetic trees and the proposal of possible modes of rhizobial evolution (7,14,31,33,35).…”

“…The main properties of a bacterial isolate can be described by its taxonomical position in relation to other strains. There are several Rhizobium species recognized at this time (10, 1.3, 24), and knowledge of rhizobial evolution and phylogeny obtained in recent studies allows the proposal of new rhizobial taxa (3,16,25). However, the current systematic description of the genus Rhizobium does not include many of the root nodule isolates from legumes of tropical (22, 37), arctic (21), and temperate (5, 12, 17) regions.…”

Tolerância de bactérias diazotróficas simbióticas à salinidade in vitro

“…Esse meio de cultura é utilizado para discriminar espécies de rizóbio (WANG et al, 1998;MARTINEZ-ROMERO et al, 1991). Como a composição original do meio LB apresenta 10 g L -1 de NaCl, para este estudo, além dessa concentração, foram também testadas as seguintes concentrações: 1, 2; 2,5; 3; 20; 30 e 50 g L -1 .…”

“…Nesse meio, a fonte principal de carbono é a peptona de caseína, que representa um fator limitante para o crescimento de algumas espécies bacterianas, pois, nem todas têm capacidade de degradá-la em meio de cultura. Essa característica tem sido usada como diferencial para a descrição de novas espécies bacterianas, inclusive rizóbio (WANG et al, 1998;MARTINEZ-ROMERO et al, 1991).…”

The effect of inoculation of an indigenous bacteria on the early growth of Acacia farnesiana in a degraded area

“…It is very well know that symbiotic relationship between shrub legumes and rhizobia is rather promiscuous and frequently unspecifi c (FRIONI et al, 1998;PUEPPKE;BROUGHTON, 1999;THRALL et al, 2001). On the other hand, in cross nodulation in greenhouse experiments, among different species and rhizobia strains (Center for Genomic Sciences, UNAM collection), a positive nodulation of A. farnesiana inoculated with Rhizobium etli (CFN42 T ), a Phaseolus vulgaris nodulant (very abundant in Mesoamerican soils) (SEGOVIA et al, 1993) was found (MARTÍNEZ-ROMERO et al, 1991). At the same time, S. americanum is able to nodulate under laboratory conditions, the very same hosts as R. etli and R. tropici and it also nodulates other Acacia species (TOLEDO, 2003).…”