Complementary Methods for the Differentiation of Rhizobium meliloti Isolates

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Isolates of Rhizobium meliloti , representing antigenically distinct indigenous serogroups 31 and 17, were grown in yeast extract-mannitol broth (YEM) containing NaCl or polyethylene glycol (PEG) to provide external water potentials ranging from −0.15 to −1.5 MPa. Several differences were found between representatives of the two groups in their abilities to adapt to water stress induced by the nonpermeating solute PEG. At potentials below −0.5 MPa, strain 31 had a lower specific growth rate than strain 17 and an irregular cell morphology. In contrast, neither growth nor cell morphology of either strain was affected significantly over the same range of water potentials created by a permeating solute, NaCl. Despite the superior growth of strain 17 at the low water potentials imposed by PEG, upshock of water-stressed cells (−1.0 MPa; PEG) into normal YEM (−0.15 MPa) resulted in a faster recovery of growth by strain 31 than by strain 17. Different responses of the two strains to a water potential increase were also revealed in nodulation studies. Strain 31 required significantly fewer days to nodulate alfalfa than strain 17 did when the strains were transferred from YEM with PEG at −1.0 MPa onto the roots of alfalfa seedlings in plant growth medium (−0.1 MPa). The addition of supplemental calcium (0.1 mM) to growth medium with PEG (−1.0 MPa) reduced the differences between strains in their responses to water stress. The severe growth restriction and morphological abnormalities shown by strain 31 were corrected, and the prolonged recovery time shown by water-stressed cells (−1.0 MPa; PEG) of strain 17 upon transfer to normal YEM was shortened. The latter strain also nodulated earlier and more rapidly after growth in PEG medium at −1.0 MPa in the presence of supplemental calcium ions. These results indicate that the efficacy of osmoregulation can vary among strains of the same species and that the mechanism of osmoregulation may differ depending on the nature of the water stress.

Section: Resultsmentioning

confidence: 99%

Growth and Nodulation Responses of Rhizobium meliloti to Water Stress Induced by Permeating and Nonpermeating Solutes

Busse

Bottomley

1989

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“…meliloti strains exhibited the highest incidence of reactions of identity between heterologous strains, but again, as was the case with R. trifolii, none were found to be identical in their spectrum of reactions against all the antisera tested (data not shown). The wide cross-reactivity among strains of R. meliloti, especially among those that have been maintained in culture, is well known (15,19,27,33).…”

Section: Resultsmentioning

confidence: 99%

“…It would be impracticable and expensive, in terms of antisera, to examine every Rhizobium isolate against stan-dard sets of antisera before making identifications of field isolates. However, it is important that the serological relationships among strains used in such experiments be investigated comprehensively, preferably in advance, in order to have increased confidence in the interpretation of the results (15,23,30).…”

Section: Resultsmentioning

confidence: 99%

Numerical Taxonomic Analysis of Some Strains of Rhizobium spp. That Uses a Qualitative Coding of Immunodiffusion Reactions

Dudman

Belbin

1988

Antigenic relationships among seven strains of Bradyrhizobium japonicum were examined by immunodiffusion reactions, in which cells of each strain were reacted against each of the seven corresponding antisera. Similar analyses were performed with Rhizobium trifolii (28 strains), Rhizobium meliloti (9 strains), and rhizobia of the cowpea miscellany (13 strains). Antigens and antisera were reacted within each species only; serological interspecies cross-reactions were not performed. The results, scored qualitatively as reactions of identity, cross-reactions, or no reaction, were formed into datum matrices and used to analyze the relationships between strains by applying the association measure of Bray and Curtis (

“…The use of electrophoretic protein profiles in the analysis of closely related isolates of Rhizobium has been described (14,26). Figure 4 shows the cytochrome and protein profiles for two strains of 0403 in YE2 (8) broth.…”

Section: Resultsmentioning

confidence: 99%

Rhizobium trifolii 0403 Is Capable of Growth in the Absence of Combined Nitrogen

Urban

Davis

Brown

1986

Rhizobium trifolii 0403 was treated with 16.6 mM succinate and other nutrients and thereby induced to grow in nitrogen-free medium. The organism grew microaerophilically on either semisolid or liquid medium, fixing atmospheric nitrogen to meet metabolic needs. Nitrogen fixation was measured via 15N incorporation (18% 15N enrichment in 1.5 doublings) and acetylene reduction. Nitrogen-fixing cells had a Km for acetylene of 0.07 atm (ca. 7.09 kPa), required about 3% oxygen for optimum growth in liquid medium, and showed a maximal specific activity of 5 nmol of acetylene reduced per min per mg of protein at 0.04 atm (ca. 4.05 kPa) of acetylene. The doubling time on N-free liquid medium ranged from 1 to 5 days, depending on oxygen tension, with an optimum temperature for growth of about 30°C. Nodulation of white clover by the cultures showing in vitro nitrogenase activity indicates that at least part of the population maintained identity with wild-type strain 0403.