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  • 1
    Electronic Resource
    Electronic Resource
    Bradyrhizobium japonicum mutants defective in root-nodule bacteroid development and nitrogen fixation (1986)
    Springer
    Archives of microbiology 144 (1986), S. 355-366 
    Details
    ISSN: 1432-072X
    Keywords: Bradyrhizobium ; Electron microscopy ; Mutants ; Nitrogen fixation ; Nodulation ; Soybean ; Symbiosis ; Transposon Tn5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod+Fix- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif+ ex planta. Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons. Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(35S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409885
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  • 2
    Electronic Resource
    Electronic Resource
    A millimeter/submillimeter spectrometer for high resolution studies of transient molecules (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1517-1522 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A design is presented for a millimeter/submillimeter direct absorption spectrometer for studies of the pure rotational spectra of metal-bearing free radicals. The spectrometer operates in the frequency range of 65–550 GHz with an instrumental resolution of 200–1000 kHz and an absorption sensitivity of a few ppm. The instrument utilizes phase-locked Gunn oscillators as the tunable, coherent source of radiation from 65–140 GHz. Higher source frequencies are obtained with Schottky diode multipliers. The gas cell and optics path are designed utilizing Gaussian beam optics to achieve maximum interaction between molecules and the mm-wave radiation in the reaction region. Scalar feedhorns and a series of PTFE lenses are used to propagate the source signal. The gas cell is a cylindrical tube 0.5 m in length with a detachable Broida-type oven. The detector for the spectrometer is a helium-cooled InSb hot electron bolometer. Phase-sensitive detection is achieved by FM modulation of the Gunn oscillators and use of a lock-in amplifier. Spectra are recorded by electrical tuning of the Gunn oscillator, which is done under computer control. The millimeter and sub-mm rotational spectra of several free radicals have been observed for the first time using this instrument, including CaOH, MgOH, CaH, MgF, and BaOH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144885
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  • 3
    Electronic Resource
    Electronic Resource
    Appearance of a novel form of plant glutamine synthetase during nodule development in Phaseolus vulgaris L. (1983)
    Springer
    Planta 157 (1983), S. 254-258 
    Details
    ISSN: 1432-2048
    Keywords: Glutamine synthetase ; Leghaemoglobin ; Nitrogenase ; Nitrogen fixation ; Phaseolus ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activities of glutamine synthetase (GS), nitrogenase and leghaemoglobin were measured during nodule development in Phaseolus vulgaris infected with wild-type or two non-fixing (Fix-) mutants of Rhizobium phaseoli. The large increase in GS activity which was observed during nodulation with the wild-type rhizobial strain occurred concomitantly with the detection and increase in activity of nitrogenase and the amount of leghaemoglobin. Moreover, this increase in GS was found to be due entirely to the appearance of a novel form of the enzyme (GSn1) in the nodule. The activity of the form (GSn2) similar to the root enzyme (GSr) remained constant throughout the experiment. In nodules produced by infection with the two mutant strains of Rhizobium phaseoli (JL15 and JL19) only trace amounts of GSn1 and leghaemoglobin were detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405190
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  • 4
    Electronic Resource
    Electronic Resource
    A mutation that blocks exopolysaccharide synthesis prevents nodulation of peas by Rhizobium leguminosarum but not of beans by R. phaseoli and is corrected by cloned DNA from Rhizobium or the phytopathogen Xanthomonas (1986)
    Springer
    Molecular genetics and genomics 203 (1986), S. 320-323 
    Details
    ISSN: 1617-4623
    Keywords: Exopolysaccharide ; Legume ; Nodules ; Rhizobium ; Xanthomonas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A Tn5-induced mutant strain of R. phaseoli which failed to synthesize exopolysaccharide (EPS) was isolated and was shown to induce normal nitrogen-fixing nodules on Phaseolus beans, the host of this Rhizobium species. The corresponding wild-type Rhizobium DNA was cloned in a wide host-range vector and by isolating Tn5 insertions in this cloned DNA, mutations in a gene termed pss (polysaccharide synthesis) were isolated. These were introduced by marker exchange into near-isogenic strains of R. leguminosarum and R. phaseoli which differed only in the identity of their symbiotic plasmids. Whereas the EPS-deficient mutant strain of R. phaseoli induced normal nitrogen-fixing nodules on Phaseolus beans, the same mutation prevented nodulation of peas by a strain of R. leguminosarum which normally nodulates this host. Further, it was found that DNA cloned from the plant pathogen Xanthomonas campestris pathover campestris could correct the defect in EPS synthesis in R. leguminosarum and R. phaseoli and also restored the ability to nodulate peas to the pss::Tn5 mutant strain of R. leguminosarum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333974
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  • 5
    Electronic Resource
    Electronic Resource
    psi, a plasmid-linked Rhizobium phaseoli gene that inhibits exopolysaccharide production and which is required for symbiotic nitrogen fixation (1985)
    Springer
    Molecular genetics and genomics 200 (1985), S. 278-282 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A strain of R. phaseoli cured of its symbiotic plasmid, pRP2JI, retained the ability to make exopolysaccharide (EPS). However, a region of pRP2JI, when cloned at an increased copy number in wide host-range vectors and transferred to this and other strains of Rhizobium, inhibited EPS synthesis. The gene responsible was termed psi (polysaccharide inhibition) and was located in a region of the symbiotic plasmid close to nodulation and nitrogen fixation genes. psi is important in the symbiosis since a wild-type strain containing psi cloned on a multicopy plasmid failed to form Phaseolus nodules, and mutant strains containing psi::Tn5 mutations failed to fix nitrogen in Phaseolus nodules. It is proposed that the function of psi may be to repress in the bacteriod the expression of genes such as those for EPS synthesis which are normally expressed in free-living culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425436
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  • 6
    Electronic Resource
    Electronic Resource
    Identification of two classes of Rhizobium phaseoli genes required for melanin synthesis, one of which is required for nitrogen fixation and activates the transcription of the other (1987)
    Springer
    Molecular genetics and genomics 207 (1987), S. 155-160 
    Details
    ISSN: 1617-4623
    Keywords: Gene regulation ; Melanin synthesis ; Nitrogen fixation ; Phaseolus beans ; Rhizobium phaseoli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The symbiotic plasmid pRP2JI of Rhizobium phaseoli strain 8002 was shown to contain two separate regions of DNA which are required and sufficient for the synthesis of the pigment melanin. One of these regions containing the class II mel gene(s) was located to other genes involved in nodulation and in nitrogen fixation. Mutations in this region abolished both the ability to synthesize melanin and to fix nitrogen in Phaseolus bean root nodules. Mutations in the other, unlinked region, containing class I mel gene(s), also abolished melanin synthesis but did not affect symbiotic nitrogen fixation. Transcriptional fusions between the class I mel gene and the Escherichia coli lacZ gene were constructed and it was demonstrated that the class II mel gene(s) activated their transcription in free-living culture. Further, strains containing the cloned regulatory class II gene(s) synthesized melanin when growing in minimal medium, in contrast to wild-type strains which became pigmented only in complete medium containing yeast extract and tryptone. It was shown by hybridization experiments that the regulatory mel gene was closely linked to or may correspond to the regulatory nifA gene; a fragment of R. phaseoli DNA which included the class II gene(s) of R. phaseoli hybridized to a previously identified nifA-like gene of R. leguminosarum, the species that nodulates peas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331503
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  • 7
    Electronic Resource
    Electronic Resource
    Plasmid-determined nodulation and nitrogen-fixation abilities inRhizobium phaseoli (1982)
    Springer
    Molecular genetics and genomics 186 (1982), S. 449-452 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary InRhizobium phaseoli strain 8002, the 190 Md plasmid pRP2JI which determines the ability to produce nitrogen-fixing nodules onPhaseolus beans (Nod+ Fix+) and the production of melanin on L-tyrosine-containing media (Mel+), was shown to be transmissible by conjugation to otherRhizobium strains. When pRP2JI was transferred to Nod- strains ofR. leguminosarum (which normally nodulates peas) the transconjugants gained the ability to nodulatePhaseolus beans and to make melanin. Out of 187 derivatives of strain 8002 carrying pRP2JI plasmids into which the transposon Tn5 had been inserted, six were Fix- Nod+ Mel+, one was Fix- Nod+ Mel- and four were Fix+ Nod+ Mel-. Three other derivatives of strain 8002 were Nod- Mel-; these had suffered deletions of c 30 Md in pRP2JI. Thus the genes for melanin production and nodulation appear to be closely linked, but melanin production is not necessary for the induction of nitrogen-fixing nodules onPhaseolus beans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00729468
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