Numerical Taxonomy of Rhizobium Strains from Legumes of the Temperate Zone

Abstract

Phenotypic properties (growth characteristics, utilization of carbon and nitrogen sources, and intrinsic antibiotic resistance) of 53 Rhizobium strains isolated from root nodules of the temperate-zone legumes Astragalus spp. (29 strains), Oxytropis campanuhta (7 strains), Hedysarum alpinum (7 strains), Ononis awensis (3 strains), Glycyrrhiza spp. (4 strains), and Coronilh varia (3 strains) were compared with those of other Rhizobium, Bradyrhizobium, and Agrobacterium strains. The final matrix, containing 83 strains and 56 nonsymbiotic features, was used for computer cluster analysis. The dendrogram showed that the new strains of temperate-zone rhizobia formed a cluster separate from both Rhizobium and Bradyrhizobium spp. Two large groups of temperate-zone rhizobia were revealed. Group 1 included rhizobial strains originating from different geographical regions with a temperate climate, while group 2 included strains from the same geographical origin, South Siberia. The 'strains of recognized Rhizobium species were clustered, in general, with each other as expected from phylogenetic relatedness.Root nodule bacteria of the genera Rhizobium and Bradyrhizobium are a common microflora of temperate soils. These bacteria may interact with the roots of leguminous plants, inducing the formation of nodules in which the fixation of atmospheric nitrogen occurs. These bacteria are commonly used in agriculture for improvement of plant growth. The specificity of the interaction between rhizobia and legumes depends on many factors coded for by the host cultivar and bacterial genomes;. 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.The host plant specificities and phage sensitivities of Rhizobium strains from temperate-zone legume root nodules formed on Astragalus, Hedysamm, Glycywhiza, and Ononis plants were recently described (17). It was shown that these strains constitute a cross-inoculation group related to Rhizobium loti. The aim of the present work was to determine the cultural properties of these strains and to compare these properties with those of other Rhizobium species. MATERIALS AND METHODSBacterial strains. Bacterial strains used in this work are listed in Table 1. Bacteria were maintained on yeast extractmannitol (YEM) (29) agar slants at 4°C.Growth characteristics. The time necessary for full colony development on YEM agar (estimated here as a colony diameter of 2 mm) was determined. Bacterial growth on meat-peptone agar and reactions with litmus milk were determined as described earlier (11). The ability of strains to grow in the presence of 0,1...

Nodulating strains of Rhizobium loti arise through chromosomal symbiotic gene transfer in the environment.

“…The RFLP analysis showed very few bands in common between the diverse isolates and the inoculant strain, both at the whole genome level as revealed by Spe I digests and in localized regions of the chromosome as revealed by hybridizations of EcoRI digests to cosmids containing genes involved in exopolysaccharide synthesis and to randomly cloned fragments. R. loti is a heterogeneous species with some isolates that nodulate L. corniculatus sharing as little as 47% DNA-DNA homology (22) and little phenotypic similarity (44). This heterogeneity is reflected in 16S rRNA gene sequence.…”

“…Sequences from most nodule strains had a 1-bp substitution from the type strain but one had three substitutions and was identical to sequence from the type strain of R huakuii. There is normally little or no variation in 16S sequence within a bacterial species (45,46) and so the degree of variability in 16S sequence observed, together with the range in overall relatedness (22,44) (25,26) and can be cured without adversely affecting nodule formation (26,27), inferring a chromosomal location for the symbiotic genes. We did not detect plasmids in the inoculant strain or most nodule isolates and the transferred DNA seemed to be chromosomally integrated, as shown by the strain-specific pattern obtained from hybridization of nod gene probes to genomic DNA digests generated by the rare-cutting enzyme Swa I (Fig.…”

Genetic Diversity and Host Range of Rhizobia Nodulating Lotus tenuis in Typical Soils of the Salado River Basin (Argentina)

“…A comparison of REP-PCR profiles for different habitats revealed levels of similarity among isolates that ranged from 80% to less than 60%. Similarly, other authors found considerable genetic diversity among rhizobia nodulating L. corniculatus by using other methodological approaches, like DNA-DNA hybridization (11,29,30) or numerical taxonomy (48).…”

Characterization of rhizobia isolated from legume species within the genera Astragalus and Lespedeza grown in the Loess Plateau of China and description of Rhizobium loessense sp. nov.

“…The genetic diversity among rhizobia from Astragalus adsurgens in different geographical regions of China has been investigated, and bacterial lineages related to Mesorhizobium, Rhizobium and Sinorhizobium were reported (Gao et al, 2001). Different rhizobial groups were also defined among isolates from other Astragalus species in China (Wang & Chen, 1996) and in other countries (Laguerre et al, 1997;Murooka et al, 1993;Novikova et al, 1994;Wdowiak & Malek, 2000).…”