摘要:

The method of horizontal agarose gel electrophoresis was used to demonstrate the presence of indigenous plasmid DNAs in different isolates of the symbiotic cyanobacteriumAnabaena azollae. All isolates extracted from seven distinct species of the host fernAzollawere found to possess one to three cryptic plasmids ranging in sizes from 35 to 100 MDa (million daltons). Anabaenas isolated fromAzolla caroliniana,Az.nilotica, andAz.pinnataspecies contained a single plasmid band of molecular mass approximately 60 MDa, whereas other endosymbiotic cyanobacteria extracted fromAzolla filiculoides,Az.rubra,Az.mexicana, andAz.microphyllawere shown to possess two or three covalently closed circular (CCC) DNAs. Cloned DNA fragments derived from the plasmid sequences of two differentAn.azollaeisolates were used as hybridization probes. Hybridization data indicated that these symbiotic cyanobacteria possess different but related plasmid species and that it is possible to construct specific plasmid DNA probes capable of distinguishing among several strains of the symbiotic anabaenas. Several heterologous DNA probes, includingRhizobiumsymbiotic genes, were used to seek homologous sequences on theAn.azollaeplasmids. DNA sequences homologous to thenod boxandnodMNgenes were present on theAnabaenaplasmids. Moreover, homology of a keyRhizobiumexopolysaccharide (exoY) gene to theAn.azollaeCCC DNAs was detected. In addition, the introduction of theAn.azollaeplasmid clone intoRhizobiumExo−mutant (exoY) resulted in the Exo+transconjugants. Those findings suggest that some of theAn.azollaeplasmids may play a role in symbiotic interactions withAzollafem.Key words:Anabaena azollae,Azolla, symbiosis, cyanobacterium, plasmids.

ISSN:0008-4166    

DOI:10.1139/m91-027

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The oxidation of elemental sulfur by two strains ofThiobacillus thiooxidanswas studied by measuring the rate of O2consumption at various concentrations of substrate and cells. In both the laboratory strain ATCC 8085 and the mine isolate SM-6, sulfur oxidation was competitively inhibited byT.thiooxidanscells; theKivalues were 0.65 and 0.05 mg wet cells∙mL−1, respectively. The rate constants were 500 and 143 μM O2∙min−1∙mg wet cells−1∙mL−1and theKmvalues for sulfur concentration were 7.5 and 0.32% pulp density, respectively. Mine isolate SM-6 was used also to study pyrite (FeS2) oxidation by measuring the rate of O2consumption. Oxidation of both washed and unwashed pyrite samples was competitively inhibited by increasing concentrations of cells; with each sample theKivalues was 0.05 mg wet cells∙mL−1. The rate constants for each sample were also the same (100 μM O2∙min−1∙mg wet cells−1∙mL−1), but theKmvalues were different (1.11% pulp density for washed pyrite and 2.81% pulp density for unwashed pyrite). Based on the rate of Fe solubilization from the washed pyrite sample,T.thiooxidanscells oxidized the sulfide released from pyrite dissolution beyond the oxidation state of elemental sulfur.Key words:Thiobacillus thiooxidans, sulfur, pyrite, oxid

ISSN:0008-4166    

DOI:10.1139/m91-028

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In the basidiomycetous genusItersoniliathree species, viz.I.perplexans,I.pyriformans, andI.pastinacae, have been described. We studied mole percentage G+C, nDNA–nDNA homology, and electrophoretic karyotypes of strains belonging to these species. Our results support the recognition of only one species, viz.I.perplexans. Changes in the electrophoretic karyotypes were observed after the transition from monokaryotic yeast cells to monokaryotic hyphae. The apomictic life cycle is described, and aspects of pathogenicity are discussed.Key words:Itersonilia, DNA, karyotyping, taxonomy.

ISSN:0008-4166    

DOI:10.1139/m91-029

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In a study of dominant diazotrophic bacteria present in the rhizosphere of wheat and maize, 28 strains ofEnterobacteriaceaewere isolated. They were all Voges-Proskauer positive, motile at 28 °C but not at 37 °C, and they produced a Tween-80 esterase and did not exhibit decarboxylase activity. This fits well with the description ofRahnella aquatilis. The ability of these strains to reduce acetylene in pure culture and in association with their host plant and the DNA hybridization with anifHDKprobe are described. This is the first time thatR.aquatilisis reported as a rhizosphere-associated bacterium and also a nitrogen fixer.Key words:Rahnella aquatilis, rhizosphere, wheat, maize, nitrogen fixation.

ISSN:0008-4166    

DOI:10.1139/m91-030

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Colonization and infection evoked specific immunoglobulin responses toCandida albicansantigens in gnotobioticnu/+mice which appeared to correlate with clearance of infected mucosal surfaces (tongue and stomach). Conversely, colonized and infectednu/numice formed some IgM but no detectable IgG or IgA antibodies againstC.albicansantigens. Although chronic mucosal infections of tongue and stomach persisted innu/numice, they were able to resist overwhelming mucosal and systemic infections withC.albicans. Thus,C.albicansspecific antibodies may play a role in clearance of mucosal candidiasis (tongue and stomach), but these antibodies do not appear to be necessary for protecting athymic mice against systemic candidiasis of endogenous origin.Key words: candidiasis, antibody response, mucosal candidiasis, murine candidiasis.

ISSN:0008-4166    

DOI:10.1139/m91-031

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Malolactic enzyme of lactic acid bacteria catalyzes the decarboxylation ofL-malate toL-lactate. The appropriate enzyme ofLactobacillus casei,Leuconostoc oenos, andLeuconostoc mesenteroides, as well as the malic enzyme ofLactobacillus casei, were purified to electrophoretic homogeneity by salmine sulphate precipitation, ion-exchange chromatography, hydrophobic chromatography, and gel filtration. The malolactic enzymes investigated were similar and showed only minor variations in the isoelectric point and the temperature optimum. The molecular weight of the subunit of all malolactic enzymes was about 65 000. Aggregates were formed, depending on the pH. The optimum activity of malolactic enzyme was observed at pH 5.8–6.0, and at this pH the dimer was stable. In addition to Mn2+and NAD, the malolactic enzyme required K+, which was replaceable by NH4+, for maximum activity. TheKmvalues forL-malate were 10.9 mM (Leuconostoc mesenteroidesB116) and 3 mM (Leuconostoc oenos). TheKmvalues for Mn2+were 0.1 mM (Leuconostoc mesenteroidesB116) and 0.017 mM (Leoconostoc oenos). Malic enzyme oxidatively decarboxylatesL-malate to pyruvate. This enzyme consists of a 37 000 subunit that forms dimers and tetramers. The NAD-dependent malic enzyme ofLactobacillus caseidecarboxylates oxalacetate and is therefore regarded as aL-malate:NAD+oxidoreductase (oxalacetate decarboxylating), EC 1.1.1.38.Key words: malolactic enzyme, malic enzyme,Lactobacillus,Leuconostoc.

ISSN:0008-4166    

DOI:10.1139/m91-032

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The effects of fungal endoparasites, attacking the eggs of the cereal cyst nematodeHeterodera avenae, and details of the infection process were studied by low-temperature scanning electron microscopy. Some female nematodes, even young ones containing no eggs, were colonized by fungi. Spores and hyphae similar to those ofNematophthora gynophilawere found in infected specimens. Fungi colonized both roots and nematodes. In early stages of infection, fungi developed within the female nematode between the organs, presumably using the female's body as a food source. In some immature females, the fungi appeared to have destroyed the uterus. In old females, appressoria ofVerticilliumspp., includingV.chlamydosporium, penetrated the eggs they contained and progressively destroyed their contents until the egg shell was filled with hyphae and spores. Only rarely were second-stage juveniles within eggs infected by these fungi. Fungal infection of eggs, which arrests their development at an early stage, therefore occurs predominantly in females rather than in newly formed cysts.Key words:Heterodero avenae, fungal parasites, naturally infested soil, scanning electron microscopy.

ISSN:0008-4166    

DOI:10.1139/m91-033

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Nuclear magnetic resonance spectra of cultures ofCandida albicansincubated in the presence of15N-labelled ammonium demonstrated that glutamine and glutamate were the only initial products of ammonium assimilation. The nature of the route of assimilation in the yeastsCandida albicans,Saccharomyces cerevisiae, andCandida tropicaliswas further examined by the use of the short-lived isotope13N. [13N]ammonium was generated in the reaction16O(p,α)13N, induced by proton bombardment of water in a tandem accelerator. High-pressure liquid chromatography was used to separate and identify the products of assimilation, and radioactivity was detected and corrected for decay, using a computer-linked Nal scintillation detector. In the three yeasts studied, the labelled ammonium was assimilated into the acid-extractable fraction of cell suspensions within 1 min, and over 75% was converted to glutamine and glutamate. Subsequent to exhaustion of the labelled ammonium, the stoichiometry of the distribution of radiolabel was consistent with a net transfer of radiolabel from glutamine to glutamate, confirming the operation of glutamate synthase (EC 1.4.1.14) in these yeasts. Initial assimilation of label was mostly into glutamine (at a maximal rate within 10 s inC.albicans), whereas accumulation in glutamate did not occur at maximal rate until more than 70% of the labelled ammonium had been assimilated (between 30 and 60 s inC.albicans). We conclude that the glutamine synthetase – glutamate synthase pathway is the major route of ammonium assimilation inC.albicansand also in nitrogen-starved cultures ofS.cerevisiaeandC.tropicalis.Key words:Candida albicans, ammonium assimilation, nitrogen.

ISSN:0008-4166    

DOI:10.1139/m91-034

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Multivalent forms of neoglycoproteins and polyacrylamides containing sialic acid were prepared and shown to be potent inhibitors of influenza A virus (H3N2) hemagglutinin with chick red blood cells. The synthetic sialylated glycoconjugates, although they were neuraminidase substrates, did not suppress viral neuraminidase and did not reduce infectivities in chick embryos. The copolyacrylamide conjugate containing a spacer group of ~11 Å (1 Å = 0.1 nm) between the polymer backbone and the sialic acid residues was the best hemagglutinin inhibitor. Moreover, it exhibited promising interferon-inducing properties.Key words: Influenza A virus, sialic acid, inhibitor, hemagglutinin, interferon.

ISSN:0008-4166    

DOI:10.1139/m91-035

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Uptake of a variety of metabolites byBradyrhizobium japonicumbacteroids under aerobic conditions was studied with the goal of identifying factors that would influence the accuracy of kinetic parameters. Saturable and nonsaturable components of absorption were identified, allowing separate analysis of only the active component. A significant proportion of labeled substrate was released as CO2. The CO2release was linear with time and occurred without a noticeable lag period. The kinetic parameters of saturable, active uptake indicated that if the label converted to CO2was ignored, this would result in underestimation of the total uptake of malate by more than 50%. The proportion of the labeled substrate converted to CO2depended on the compound but was high in all cases. Glucose showed the smallest difference, with 13% of the label converted to CO2in a 5-min incubation. The uptake of glutamate was inhibited by aspartate, whereas no effect by equimolar dicarboxylic acids was found. Succinate or fumarate inhibited malate uptake, whereas amino acids showed no effect. Thus, organic acids appeared to have a common carrier distinct from that for amino acids. Techniques for separation of active and passive uptake components and for collection and analysis of CO2respired are described; these techniques should be used for accurate analysis of metabolite uptake.Key words:Bradyrhizobium japonicum, bacteroids, metabolite uptake, CO2.

ISSN:0008-4166    

DOI:10.1139/m91-036

出版商:NRC Research Press    

年代:1991

数据来源: NRC