Genotypic and Phenotypic Comparisons of Chromosomal Types within an Indigenous Soil Population of
            <i>Rhizobium leguminosarum</i>
            bv. trifolii

Leung, Kamtin; Strain, Steven R.; Bruijn, Frans J. de; Bottomley, Peter J.

doi:10.1128/aem.60.2.416-426.1994

Cited by 55 publications

(30 citation statements)

References 60 publications

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“…Wayne et al (1987) suggested that a species 'would include strains with approximately 70% or greater DNA-DNA relatedness.' Previous studies have shown a strong correlation between DNA-DNA hybridization values and estimates of genetic relatedness based on MLEE (Selander et al Leung et al 1994a). Based on our MLEE results, the genetic distance between Ei Ts 1 & 2, ET 3, ETs 4-8 and ETs 9-17 indicates that there may be u p to four species within this population.…”

Section: Discussionmentioning

confidence: 93%

Diversity and genetic structure of a natural population of Rhizobium leguminosarum bv. trifolii isolated from Trifolium subterraneum L.

et al. 1995

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A collection of 121 isolates of Rhizobium leguminosarum biovar (bv.) trifolii was obtained from root nodules of Trifolium subterraneum L. (subclover) plants growing in an established pasture. The collection consisted of a single isolate from each of 18 plants sampled from seven microplots. The following year, a further 28 and 27 isolates were collected from the first and seventh sampling points, respectively. Analysis of restriction fragment length polymorphisms (RFLPs) of both chromosomal and Sym (symbiotic) plasmid DNA and multilocus enzyme electrophoresis (MLEE) were used to assess the diversity, genetic relationships and structure of this population. Symbiotic effectiveness tests were used to examine the symbiotic phenotype of each isolate collected in the first year. Analysis of RFLPs of the first year isolates revealed 13 chromosomal types and 25 Sym plasmid types. Similar Sym plasmid types were grouped into 14 families containing 1–6 members. No new chromosomal types and six new Sym plasmid types were detected in the second year. The symbiotic effectiveness of the first year isolates of the same Sym plasmid type was similar. Significant differences in symbiotic effectiveness were detected between different Sym plasmid types in the same plasmid family. Representative isolates of each chromosomal type Sym plasmid type identified in the first year were analysed using multilocus enzyme electrophoresis. Mean genetic diversity per locus was high (0.559). Enzyme electrophoresis revealed 17 electrophoretic types (ETs). Ouster analysis of the enzyme data revealed large genetic diversity amongst the ETs. Strong linkage disequilibrium was observed for the population as a whole, i.e. clonal population structure, but significantly less disequilibrium was observed among a cluster of ETs suggesting that recombination occurred between ETs within the cluster. Our results revealed that a population of naturally occurring isolates of Rhizobium leguminosarum bv. trifolii can be genetically diverse and support the possibility that recombination plays a role in generating new genotypes.

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Section: Discussionmentioning

confidence: 93%

Diversity and genetic structure of a natural population of Rhizobium leguminosarum bv. trifolii isolated from Trifolium subterraneum L.

et al. 1995

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“…chvA and chvB homologous to A. tumefaciens genes) for the early phases during plant colonisation in the di¡erent plant-associated bacteria [50]. Two of the remarkable characteristics of plant-associated bacteria are their high genetic diversity found world-wide and their clonal population structure encountered in speci¢c ecosystems [52,56,64,65].…”

Section: Local Adaptations and Plasmidsmentioning

confidence: 99%

Genome evolution within the alpha Proteobacteria: why do some bacteria not possess plasmids and others exhibit more than one different chromosome?

Moreno

1998

FEMS Microbiology Reviews

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Animal intracellular Proteobacteria of the alpha subclass without plasmids and containing one or more chromosomes are phylogenetically entwined with opportunistic, plant-associated, chemoautotrophic and photosynthetic alpha Proteobacteria possessing one or more chromosomes and plasmids. Local variations in open environments, such as soil, water, manure, gut systems and the external surfaces of plants and animals, may have selected alpha Proteobacteria with extensive metabolic alternatives, broad genetic diversity, and more flexible and larger genomes with ability for horizontal gene flux. On the contrary, the constant and isolated animal cellular milieu selected heterotrophic alpha Proteobacteria with smaller genomes without plasmids and reduced genetic diversity as compared to their plant-associated and phototrophic relatives. The characteristics and genome sizes in the extant species suggest that a second chromosome could have evolved from megaplasmids which acquired housekeeping genes. Consequently, the genomes of the animal cell-associated Proteobacteria evolved through reductions of the larger genomes of chemoautotrophic ancestors and became rich in adenosine and thymidine, as compared to the genomes of their ancestors. Genome organisation and phylogenetic ancestor-descendent relationships between extant bacteria of closely related genera and within the same monophyletic genus and species suggest that some strains have undergone transition from two chromosomes to a single replicon. It is proposed that as long as the essential information is correctly expressed, the presence of one or more chromosomes within the same genus or species is the result of contingency. Genetic drift in clonal bacteria, such as animal cell-associated alpha Proteobacteria, would depend almost exclusively on mutation and internal genetic rearrangement processes. Alternatively, genomic variations in reticulate bacteria, such as many intestinal and plant cell-associated Proteobacteria, will depend not only on these processes, but also on their genetic interactions with other bacterial strains. Common pathogenic domains necessary for the invasion and survival in association with cells have been preserved in the chromosomes of the animal and plant-associated alpha Proteobacteria. These pathogenic domains have been maintained by vertical inherence, extensively ameliorated to match the chromosome G + C content and evolved within chromosomes of alpha Proteobacteria.

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“…However, the nature of ecotypic structure is poorly understood for most bacterial populations, both because the relevant environmental niche differences are often unknown and because there are few data on the distribution of ETs across specific habitats. For symbiotic nitrogen fixing bacteria, a number of studies have characterized patterns of genetic diversity using multilocus enzyme electrophoresis (Young 1985;Pinero et al 1988;Eardly et al 1990;Souza et al 1992;Leung et al 1994, Souza et al 1994). However, most previous work has not examined intrapopulation associations between bacterial ETs and host plants.…”

Section: Bacterial Genotypes In Other Populationsmentioning

confidence: 99%

NONRANDOM GENOTYPIC ASSOCIATIONS IN A LEGUME— BRADYRHIZOBIUM MUTUALISM

1996

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Abstract.-Genetically divergent lineages often coexist within populations of the annual legume Amphicarpaea braeteata. At one site dominated by two such lineages (termed biotypes "C" and "S"), isolates of root-nodule bacteria (Bradyrhizobium sp.) were sampled from both hosts and analyzed by enzyme electrophoresis. Symbiont populations on the two plant biotypes were highly distinct. Out of 15 bacterial multilocus genotypes detected (among 51 isolates analyzed), only one was shared in common by the two plant biotypes. Cluster analysis revealed three bacterial lineages (designated I, II, and III), with lineage I found exclusively on biotype C plants, and the two other lineages almost completely restricted to biotype S hosts. Laboratory inoculation tests indicated that lineage I bacteria were strictly specialized on biotype C hosts, forming few or no nodules on plants of the other host biotype. Bacterial lineages II and III were capable of forming nodules on both kinds of plants, but nodule numbers were often significantly higher on biotype S hosts. The nonrandom association between plant and bacterial lineages at this site implies that genetic diversity of hosts is an important factor in the maintenance of polymorphism within the symbiont population.Key words.-Bacteria, Bradyrhizobium, coevolution, legumes, linkage disequilibrium, mutualism, nitrogen fixation, polymorphism, symbiosis.Received April 12, 1994. Accepted September 21, 1994 Although it is widely accepted that host-parasite interactions should generate genetic polymorphism (Haldane 1949;Clarke 1976;Hamilton 1982), the situation is much less clear in mutualistic interactions among species. In host-parasite interactions, parasite specialization on hosts with a particular defense mechanism can result in frequency-dependent disease impact on hosts, leading to stable or cyclic polymorphisms in both species (Lewis 1981;Seger 1988). Law (1985) argued that quite different evolutionary processes should occur in mutualisms. Selection on each species in a mutualism will favor adaptation to the most prevalent phenotype in the other species, because individuals adapted only to rare phenotypes will receive fewer mutualistic benefits given their smaller chance of encountering a suitable partner. As a result, Law suggested that the evolutionary trend toward genotypic specialization thought to typify host-parasite coevolution should generally be lacking in mutualisms. Because polymorphism due to frequency-dependent disease impact requires parasite specialization (Lewis 1981;Seger 1988; Parker 1992a), the absence of such specialization in mutualisms would also imply the absence of any inherent tendency toward genetic polymorphism.However, this argument ignores the fact that different mutualist partners may vary widely in the fitness benefits that they can provide, with the optimal partner unlikely to be identical for all conspecific individuals. Thus, selection in mutualisms may favor intrapopulation specialization, if mechanisms exist to exclude incompatible partners and...

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Genotypic and Phenotypic Comparisons of Chromosomal Types within an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii

Cited by 55 publications

References 60 publications

Diversity and genetic structure of a natural population of Rhizobium leguminosarum bv. trifolii isolated from Trifolium subterraneum L.

Diversity and genetic structure of a natural population of Rhizobium leguminosarum bv. trifolii isolated from Trifolium subterraneum L.

Genome evolution within the alpha Proteobacteria: why do some bacteria not possess plasmids and others exhibit more than one different chromosome?

NONRANDOM GENOTYPIC ASSOCIATIONS IN A LEGUME— BRADYRHIZOBIUM MUTUALISM

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