Rhizobium Population Genetics: Genetic Variation Within and Between Populations from Diverse Locations

Abstract

Polyacrylamide gel electrophoresis (PAGE) of isoenzymes of chromosomal origin, and plasmid profile analyses, were used to investigate genetic variation within and between natural populations of Rhizobium leguminosarum biovar trifolii from diverse sources. PAGE showed that, within the biovar in general, relatively few alleles existed for the enzyme loci studied. There was a strong genetic disequilibrium between loci, suggesting that chromosomal recombination is rare. Both PAGE and plasmid profile analysis revealed differences in the degree of strain polymorphism at the sites examined. At sites which were acidic, improved (by liming) and neutral, strain variation was found to be low, intermediate and high, respectively.

Higher Diversity of Rhizobium leguminosarum Biovar viciae Populations in Arable Soils than in Grass Soils

“…Such complex models are not robust given the available data and were not considered further. A positive relationship has previously been observed between the number of plasmid profiles and pH (7).…”

“…Heavy metals have increased mobility in acidic soils and have a negative relationship with diversity (9). Decreases in diversity in acidic and metal-polluted soils have been accompanied by reductions in rhizobial density (7,9).…”

“…We analyzed each soil sample in duplicate in order to determine whether there are specific soil parameters that influence rhizobial diversity. Factors were chosen that have been shown to influence rhizobial diversity (pH [7] and magnesium [15]), cell functioning (calcium [31] and magnesium [29]), or bacterial survival (clay [3]) and that can be expected to change according to the land management (conductivity, mineral nitrogen, organic content, potential nitrogen, phosphate, and clay). The results are shown in Table 3.…”

“…The replication allows us to assess the difference in rhizobial diversity between arable and grass management systems while taking into account the inevitable variation from site to site. R. leguminosarum genotypes are not evenly distributed across the United Kingdom (7,36). The soil type can affect microbial activity (6), possibly due to differences in the distribution of suitable niches (22) and predation pressure by protozoa (3).…”

Population genomics of Sinorhizobium medicae based on low-coverage sequencing of sympatric isolates

“…Young et al (1987) demonstrated that, for Rhizobium leguminosarum in a pea field, each nodule was essentially an independent sample and the diversity among isolates from a single plant was almost the same as between plants across a metre, while samples 20 m apart were not significantly different. Genotype frequencies do, however, vary significantly when sites are many kilometres apart, reflecting environmental differences (Harrison et al, 1989).…”