摘要:

Cytochemical localization of cellulosic β-(1–4) glucans in pea (Pisum sativumL.) nodules at different stages of infection by an effective isolate ofRhizobium leguminosarumbiovarviceaewas studied using a gold-complexed exoglucanase. Cellulose subunits were present in great amounts in root cell walls, as shown by intense and regular labeling by gold particles. Labeling was unevenly distributed over the thin walls of emerging infection threads. In more developed infection threads, labeling was more intense and evenly distributed than in emerging threads, although slightly altered, unlabeled wall areas were frequently observed at the growing tips. Droplets containing rhizobia, which originated from infection threads, were surrounded by labeled wall-like material. Rhizobial droplets were either single- or multi-celled, and were sometimes separated by inner, unevenly labeled compartments. The surrounding wall-like material was irregularly labeled, and unlabeled wall areas, neighbouring intensely labeled ones, were observed frequently. There was an absence of labeling ahead of the rhizobia that escaped from the droplets, but degenerating wall-like material was present around the escaping rhizobia, mainly on their sides. At more advanced stages of development, labeling was present only over the outermost wall layers of rhizobial droplets, indicating that inner portions were degraded first. These observations suggest that a hydrolytic enzyme is involved in the sequence of events from infection thread formation through rhizobial release in the host cell cytoplasm, and that the hydrolytic enzyme is of rhizobial origin.Key words:Rhizobium–Pisumsymbiosis, root nodules, rhizobial droplets, cellulose, colloidal gold.

ISSN:0008-4166    

DOI:10.1139/m89-138

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Repressible acid, repressible alkaline, and constitutive alkaline phosphatases were studied with respect to their control and localization in conidia ofNeurospora crassa. In contrast to constitutive alkaline phosphatase, the production and secretion of repressible phosphatases is regulated by phosphate level and pH of the culture medium. Phosphatase activity increased with conidial germination and was detectable partially in the growth medium after 5 h incubation. These enzymes were found to be located in different cell compartments. Part of the whole cell enzyme activity involved a soluble exoconidial fraction, and another part, a cell-bound enzyme that remained after successive washes. The cell-bound enzyme was sensitive to treatment with dilute acid and was thought to be located in the mural space. A third part of the enzyme activity was judged to be intracellular, as shown by treatments with surface-active agents and heat, which disrupted the conidia or destroyed the conidial permeability barriers. On the basis of these criteria, the constitutive alkaline phosphatase was considered to be more cryptic than the repressible phosphatases. The alkaline phosphatases were also active during heat treatment, suggesting they may be involved in the mechanism of secretion.Key words:Neurospora crassa, repressible acid phosphatase, repressible alkaline phosphatase, constitutive alkaline phosphatase, conidia.

ISSN:0008-4166    

DOI:10.1139/m89-139

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Two xylanases (I and II) out of several extracellular xylanases produced by the thermophilic fungusChaetomium thermophilevar.coprophilewere purified to homogeneity by a combination of ion exchange and gel filtration chromatographic procedures. They had molecular weights of 26 000 (xylanase I) and 7000 (xylanase II). The temperature optima for xylanase I and II were 70 and 60 °C, and they were optimally active at pH 4.8–6.4 and 5.4–6.0, respectively. Xylanase I was found to be comparatively more stable than xylanase II at higher temperatures. Amino acid composition indicated that xylanase I contained high amounts of glycine, threonine, and low amounts of histidine and sulphur-containing amino acids. Each enzyme released different hydrolysis products from larch wood xylan. Xylanase I produced mainly xylobiose and xylotriose whereas xylanase II produced mainly xylobiose.Key words: Xylanase, enzyme purification, characterization,Chaetomium thermophile.

ISSN:0008-4166    

DOI:10.1139/m89-140

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

A toxigenic strain ofEscherichia colidisplayed important structural modifications when placed in seawater which naturally lacked nutritive elements, as observed by electron microscopy. These include cell wall and cell body distortion, modification of the membranes, central segregation of the chromosome, and retraction of the cytoplasm. These modifications were accompanied by a decrease in cell protein content of approximately 40%. Certain cytoplasmic membrane proteins were lost, and new ones appeared. The development of these changes was considerably slower in cells that had previously been grown in a seawater medium. This suggests that osmotic regulation mechanisms, which enableE.colito survive much longer in marine conditions, may have a protective influence.Key words:Escherichia coli, structure, envelopes, survival, seawater.[Journal translation]

ISSN:0008-4166    

DOI:10.1139/m89-141

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Ribosome synthesis was studied in spores at the swelling stage and compared with freshly emerged and logarithmically growing vegetative amoebae. During the swelling stage of spore germination, ribosome synthesis was abnormal. Newly made ribosomes accumulated unequal amounts of 26S and 17S rRNAs. The stoichiometric ratio 26S:17S was 0.5 in swelling spores, compared with 0.9 in amoebae. The relative level of pre-rRNA persisting in the nucleus was apparently 2- to 3-fold higher in swelling spores than in amoebae. All of the known ribosomal proteins, except for a few, were made during the swelling stage and were associated with the newly made ribosomes in expected amounts. Analysis of the 2′-O-methyl ribose content in the newly made rRNAs suggests that methylation was defective in swelling spores. Compared with growing amoebae, the methyl content was 30 and 64% less in 26S and 17S RNAs from the swelling stage, respectively. It is suggested that undermethylation could be partly responsible for the differential accumulation of newly made 26S and 17S RNAs during the early stages of spore germination inDictyostelium discoideum.Key words: cellular slime mold, rRNA synthesis, ribosomal proteins, methylation, cell differentiation.

ISSN:0008-4166    

DOI:10.1139/m89-142

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The activity of an enzyme in the tricarboxylic acid cycle, isocitrate dehydrogenase EC 1.1.1.42 (ICD), was followed during the production of a biosurfactant, surfactin, byBacillus subtilis. A mutant suppressed the activity of the enzyme 30 times more than the parent strain and simultaneously produced three and a half times more surfactin. Decreased ICD activity could also be achieved by (i) decreased oxygen concentration, (ii) increased growth rates, and the addition of (iii) citric acid or (iv) ammonium nitrate to the production medium. The nitrogen source (namely, ammonium nitrate) was critical as neither ammonium chloride nor sodium nitrate could individually enhance biosurfactant production. Initiation of surfactin production occurred as redox values increased and ICD activity decreased. Increased surfactin yields correlated with low levels of ICD activity.Key words: biosurfactant, surfactin,Bacillus subtilis, isocitrate dehydrogenase, mutant.

ISSN:0008-4166    

DOI:10.1139/m89-143

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Twelve lytic phages that infect lactococci (eight prolate-headed and four isometric-headed phages) were compared via DNA–DNA hybridization, DNA restriction site mapping, genome size estimation, and analysis of virion proteins. Prolate-headed phages carried double-stranded DNA of 21.8 to 23.4 kilobases and showed three major virion proteins in SDS-polyacrylamide gel electrophoresis. Isometric-headed phages carried double-stranded DNA of 28.1 to 30.4 kilobases and showed one major virion protein. The DNA of all phages had cohesive ends. No DNA hybridization was observed between the two phage types. Restriction endonuclease cleavage site mapping of DNA showed similarities between some of the phages.Key words:Lactococcus lactis, bacteriophages, genome size, phage types, restriction site mapping.

ISSN:0008-4166    

DOI:10.1139/m89-144

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Transposon Tn5mutants of a wheat root growth-inhibiting nonfluorescentPseudomonassp. were inoculated into intact soil-core microcosms to determine the utility of intact soil cores for evaluating the fate and transport of microorganisms in agricultural ecosystems. Transposon Tn5mutants that no longer produced a toxin (tox−) to inhibit the growth of wheat roots orEscherichia coli, and Tn5mutants that retained the toxin-producing ability (tox+), were inoculated into plow layer soil of intact soil-core microcosms. Spring wheat was then planted, and Tn5mutant populations were enumerated over time in the bulk soil and with depth in the bulk soil, rhizosphere, and rhizoplane.Pseudomonassp. Tn5mutants were observed in soil-core leachates and in the gut of earthworms introduced into microcosms. The population of the introduced Tn5mutants declined over time in the surface soil, but colonized the wheat rhizosphere and rhizoplane throughout the 60-cm soil-core depth. Rhizoplane populations of the tox+Tn5mutants were higher than populations of tox−mutants at the seedling stage, but significant differences were not observed at later stages of plant growth or in the rhizosphere. The Tn5mutants were transported through the core with percolating water and were present in the gut of earthworms. Intact soil-core microcosms could be useful in assessing the fate and transport of genetically engineered microorganisms in the environment prior to field testing.Key words: microcosms,Pseudomonassp., rhizosphere, soil, Tn5.

ISSN:0008-4166    

DOI:10.1139/m89-145

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Quantitative measurements of bacterial growth may be made using a radioassay technique. This method measures, by scintillation counting, the14CO2derived from die bacterial metabolism of a14C-labeled substrate. Mathematical growth models may serve as reliable tools for estimation of the generation rate constant (or slope of the growth curve) and provide a basis for evaluating assay performance. Two models, i.e., exponential and logistic, are proposed. Both models yielded an accurate fit to the data from radioactive measurement of bacterial growth. The exponential model yielded high precision values of the generation rate constant, with an average relative standard deviation of 1.2%. Under most conditions the assay demonstrated no changes in the slopes of growth curves when the number of bacteria per inoculation was changed. However, the radiometric assay by scintillation method had a growth-inhibiting effect on a few strains of bacteria. The source of this problem was thought to be hypersensitivity to trace amounts of toluene remaining on the detector.Key words: bacterial growth modelling.

ISSN:0008-4166    

DOI:10.1139/m89-146

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The morphology of 49Streptomycesstrains and eight other actinomycetes was studied in shaken liquid culture, using a range of spore inocula in a complex medium. Results showed that each strain would produce one, two, or more different gross morphological types throughout the spore inoculum range tested. The morphological forms that were observed included compact pellets, spiky or fluffy pellets, oblong pellets, flakes, hydrophobic rafts, aggregates, dispersed mycelium, fragmented mycelium, or combinations of these forms. Two strains ofS.viridochromogenesdeveloped different ranges of morphology in the test conditions.Key words:Streptomyces, pellets, spore inoculum.

ISSN:0008-4166    

DOI:10.1139/m89-147

出版商:NRC Research Press    

年代:1989

数据来源: NRC