ISSN:0008-4166    

DOI:10.1139/m90-139b

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The physiology of biosurfactant synthesis by a soil isolate, identified as aRhodococcusspecies, is described. The biosurfactant is a surface-active glycolipid produced during the stationary growth phase ofRhodococcusspecies H13-A onn-alkanes and fatty alcohols in response to limiting ammonium ion concentrations. Hexadecane-grown cells produced increasing amounts of extracellular glycolipid when the carbon to nitrogen ratio (C/N) was increased from 1.7 to 3.4. The increase in extracellular glycolipid in hexadecane-grown cells correlated with a decrease in the interfacial tension of the spent growth medium to values less than 5 mN/m. Significant levels of extracellular glycolipid were not detected in the spent growth medium of cells grown on triglycerides, fatty acids, ethanol, organic acids, or carbohydrates.Rhodococcusspecies H13-A contains the three indigenous plasmids pMVS100, pMVS200, and pMVS300, with neither pMVS200 nor pMVS300 being involved in glycolipid synthesis or hexadecane dissimilation. The role of pMVS100 remains undetermined.Key words: biosurfactants, glycolipids, trehalose lipids,Rhodococcus.

ISSN:0008-4166    

DOI:10.1139/m90-127

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The chemical and physical properties of a biosurfactant synthesized by hexadecane-grownRhodococcusspecies H13-A are described. The biosurfactant is an anionic glycolipid consisting of 1 major and 10 minor components. The hydrophilic portion of the molecule is trehalose, which is acylated with normal C10to C22saturated and unsaturated fatty acids, C35to C40mycolic acids, hexanedioic and dodecanedioic acids, and 10-methyl hexadecanoic and 10-methyl octadecanoic acids. The major glycolipid species was identified as 2,3,4,6,2′,3′,4′,6′-octaacyltrehalose, plus minor glycolipid species of di-, tetra- and hexa-acyltrehalose derivatives. The glycolipid exhibited a critical micelle concentration of 1.5 mg/mL and minimum interfacial tension value of 2 × 10−2 mN/m against decane, with a further reduction in interfacial tension to 6 × 10−5 mN/m in the presence of the cosurfactant pentanol. The phase behavior of the glycolipid indicates the formation of a surfactant-rich, "middle-phase" microemulsion containing liquid crystals, both of which are associated with surfactant systems having ultralow interfacial tension values.Key words: trehalose lipids, glycolipids, biosurfactants.

ISSN:0008-4166    

DOI:10.1139/m90-128

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Yeasts (228) isolated for natural habitats were screened for their ability to produce amylases in semisolid medium of wheat bran. Strains ofAureobasidium pullulans,Candida famata, andCandida kefyrshowed high enzymatic activity for α-amylase, glucoamylase, and debranching enzyme.Key words:Aureobasidium,Candida, amylolytic yeasts, α-amylase, glucoamylase.

ISSN:0008-4166    

DOI:10.1139/m90-129

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A wild-type isolate ofEpicoccum purpurascenswas exposed to shortwave ultraviolet light. One of the resulting cultures (M-20-A) was grown on media amended with the fungicides iprodione or vinclozolin and fungicide-tolerant strains were obtained. Several comparisons were made between new strains and the wild type. Sporulation was improved compared with the wild type. Strains varied in their tolerance to iprodione and vinclozolin but were not tolerant to the fungicide benomyl. Strains R4000, 16-B, and 7-A inhibitedSclerotinia sclerotiorum in vitromore than either the wild type or M-20-A, and exhibited improved control of white mold of bean in the greenhouse compared with M-20-A.Key words: biological control, fungicide resistance, white mold, iprodione, vinclozolin.

ISSN:0008-4166    

DOI:10.1139/m90-130

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Analysis of an authentic sample of the antifungal antibiotic talaron from the biocontrol fungusTalaromyces flavusindicated that approximately 40% of the solid sample was glucose oxidase. High-performance liquid chromatography elution profiles of the antimicrobial activity of talaron coeluted with those of glucose oxidase. Fluorescence emission and excitation wavelength maxima for talaron were similar to those of glucose oxidase fromAspergillus niger. The molecular weight of talaron was 152 000 with a subunit molecular weight of 71 000. The isoelectric point of talaron was pH 4.2. Mobilities of talaron on native, sodium dodecylsulfate, and isoelectric focusing polyacrylamide gels were identical with those of glucose oxidase produced byT.flavus. Furthermore, talaron had antimicrobial activity only in the presence of glucose. Hydrogen peroxide produced by the action of glucose oxidase is toxic toVerticillium dahliae. This study indicates that the antifungal activity of authentic talaron resulted from glucose oxidase produced byT.flavus.Key words: biological control, glucose oxidase, hydrogen peroxide, talaron,Talaromyces flavus,Verticillium dahliae.

ISSN:0008-4166    

DOI:10.1139/m90-131

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

We have reexamined the properties of a gliding bacterium, Is-11, which was previously isolated from soil because of its ability to denitrify and to reduce nitrous oxide in the presence of sulfide and normally inhibitory concentrations of acetylene. Occurrence of such an organism may have important implications for the use of the acetylene inhibition assay for measuring denitrification rates in reduced, sulfidic environments. Although originally tentatively identified as aCytophagasp., extensive morphological, physiological, and biochemical tests as well as G+C analysis and DNA hybridization studies now indicate that the soil isolate Is-11 is a strain ofFlexibacter canadensis.Key words: gliding bacteria,Flexibacter canadensis, denitrification, acetylene, sulfide, nitrous oxide.

ISSN:0008-4166    

DOI:10.1139/m90-132

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Fluorescein isothiocyanate labeled lectin binding techniques have revealed differences in the distribution pattern of glycosyl residues at the cell wall level between fungi that are hosts and those that are nonhosts of the mycoparasitePiptocephalis virginiana, and at the protoplast level between compatible and incompatible hosts. The cell wall of the compatible hosts (Choanephora cucurbitarumandMortierella pusilla) and an incompatible host (Phascolomyces articulosus), as well as that of the mycoparasite itself, contains glucose andN-acetylglucosamine. However, the cell wall of a nonhost (Mortierella candelabrum) tested positive with lectins specific for various sugars, including not only glucose andN-acetylglucosamine, but also fucose,N-acetylgalactosamine, and galactose. These latter sugars could also be exposed at the surfaces of hosts and of the mycoparasite, but only after mild treatment with proteinase or when grown in a liquid culture. Pretreatment of the mycoparasite with glucose andN-acetylglucosamine inhibited its attachment to the host cell surface, but had no obvious effect on appressorium formation. On the other hand, appressorium formation was inhibited by heat treatment of host cell wall fragments which still permitted attachment, thus indicating that the factors responsible for attachment and for appressorium formation are different. The protoplast surfaces of compatible hosts contained all the sugars listed above and these protoplasts could attach to the germ tube of the mycoparasite. Only lectins specific forN-acetylglucosamine and for glucose were bound at the protoplast surface of the incompatible host; these protoplasts did not attach to the mycoparasite germ tube.Key words: mycoparasite, appressorium formation, lectins, host cell surface, attachment, protoplast surface.

ISSN:0008-4166    

DOI:10.1139/m90-133

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Thirty-four bacterial isolates from an agricultural soil anaerobically preincubated in the presence of glucose were tested for their ability to reduce nitrate to ammonia or to denitrify in two different media: nitrate broth and a minimal medium enriched with glucose. Ten isolates were considered denitrifying bacteria and 7 were dissimilatory ammonia producers. Ammonia production by the isolate identified asEnterobacter amnigenuswas quantified and attained 50% of 138 mg∙L−1of added NO3−N. The dissimilatory character of this reduction was clearly confirmed by culturing this15N-labeled bacterium in the presence of unlabeled nitrite. Nitrous oxide was produced at the same time as nitrite was reduced to ammonia. Increasing nitrate N levels from 48 to 553 mg∙L−1in culture medium resulted in an increase in the level of nitrite produced and simultaneously a decrease in ammonia and nitrous oxide production.Key words: dissimilatory nitrate reduction, dissimilatory ammonia production, denitrification,Enterobacter amnigenus,

ISSN:0008-4166    

DOI:10.1139/m90-134

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A dissimilatory ammonia-producing isolate identified asEnterobacter amnigenusand a denitrifier identified asAgrobacterium radiobacterisolated from the same soil were studied. The products of nitrate reduction in a minimal medium, enriched with glucose and containing nitrate N as the sole nitrogen source, were quantified when each of these isolates was cultured anaerobically, alone or mixed together in the presence or absence of C2H2. When they were cultured together, ammonia was the principal product of nitrate reduction. The distribution between denitrification and dissimilatory ammonia production (DAP) for nonsterilised soil samples inoculated withE.amnigenusorA.radiobacter, or a mixture of these two isolates, was also investigated. Production of NH4+was increased under these conditions (strict anaerobiosis and much available fermentable carbon), but the inoculation of soil samples with 1.2 × 107cells ofE.amnigenus·g dried soil−1was not sufficient to shift nitrate reduction from nitrous oxide (denitrification) to ammonia production, suggesting that inoculation with a greater number of DAP bacteria than introduced would probably be required to enable ammonia production to exceed nitrous oxide release.Key words: dissimilatory ammonia production, denitrification,Enterobacter amnigenus,Agrobacterium radiobacter.

ISSN:0008-4166    

DOI:10.1139/m90-135

出版商:NRC Research Press    

年代:1990

数据来源: NRC