摘要:

The effects of nitrogen and phosphorus enrichment on the colonization and decomposition of plant litter (Carex) by the microbiota of Toolik Lake, Alaska, were studied in microcosms. Added phosphorus resulted in a fourfold (p ≤ 0.01) increase in the levels of ATP associated with the microbiota on fresh litter, while nitrogen-plus-phosphorus enrichments resulted in a twofold increase in the ATP associated with the microbiota of fresh (p ≤ 0.01) or partially degraded (p ≤ 0.05) litter compared with controls. Neither nitrogen nor phosphorus enrichments, alone or together, significantly altered the observed weight loss of either fresh or partially degraded litter, although additional phosphorus was immobilized by the litter microbiota when available. Subsequent experiments demonstrated that the increase in ATP resulting from nutrient enrichment occurred when the microcosms were incubated in daylight but not in the dark, suggesting that nutrient enrichment primarily stimulated the photosynthetic component of the detrital community.

ISSN:0008-4166    

DOI:10.1139/m82-178

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The relationships between specific asexual development stages ofAspergillus parasiticusand potential enzyme markers of these stages were established. Competence was reached when culture age was 22.6 h for an initial inoculum level of 3.0 × 102conidia∙mL−1and 8.09 h for an initial inoculum level of 2.0 × 104conidia∙mL−1. The appearance of laccase activity was correlated with the development of conidia. Laccase activity was detected only in conidiating cultures. Activity was inhibited in shaking cultures due to inhibition of conidiation. Laccase activity reached a maximum in cultures after 120 h. Inducible nitrate reductase activity was detected inA.parasiticuscultures after competence was establis

ISSN:0008-4166    

DOI:10.1139/m82-179

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Spores of an albino mutant ofColletotrichum lagenariumformed colorless appressoria. The appressoria germinated laterally and formed secondary appressoria after further incubation. Appressorial formation was accompanied by nuclear division and migration of the spore contents into the primary appressorium. When the primary appressorium was mature, the nucleus in the spore had disappeared and the spore appeared empty. Similar phenomena were observed in the formation of secondary appressoria from primary appressoria. Formation of both primary and secondary appressoria was temperature sensitive. When spores were incubated in the presence of cycloheximide after 1 h of incubation, formation of primary and secondary appressoria was not affected. Secondary appressoria pigmented by addition of 3,4-dihydroxyphenylalanine could penetrate nitrocellulose membranes.

ISSN:0008-4166    

DOI:10.1139/m82-180

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Bacillus megaterium27 produces one exocellular metalloproteinase during growth as well as during sporogenesis. The formation of the enzyme during growth is repressed by the addition of amino acids of the leucine–isoleucine group. Its synthesis during sporogenesis is rather insensitive to repression. The enzyme is formed during the first 90 min after transfer to a sporulation medium, amino acids delaying only the onset of its synthesis as well as the onset of sporogenesis. The synthesis of the proteinase in asporogenicB.megateriumKM1 is repressed by amino acids during growth as well as during incubation in the sporulation medium and proceeds for a longer time under the latter condition. The results suggest that the formation of the proteinase during growth may be controlled differently from that during sporulation.

ISSN:0008-4166    

DOI:10.1139/m82-181

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The immunogenicity of antigenic fractions obtained by the extraction ofPasteurella multocidastrain X-73 (serotype 1) with potassium thiocyanate (KSCN) was determined in chickens and mice. The initial KSCN extract was centrifuged at 105 000 × g, and the antigens were separated into a particulate fraction (40p) and a soluble supernatant fraction (40s). The ultracentrifuged fractions were further resolved by preparative electrofocusing. The 40pfraction was resolved into two subgroups having isoelectric points of 3.5–3.9 and 5.5–6.0; the 40sfraction was resolved into five subgroups ranging in isoelectric points from 4.4 to 9.0. The 40pfractions were antigenically similar and contained lipopolysaccharide (LPS) and protein. The 40sfractions were antigenically distinct from the 40pfractions and from each other; they contained proteins and polysaccharides but no LPS. The 40pantigens were strongly immunogenic in mice and chickens, whereas the 40santigens were weakly immunogenic in chickens and not immunogenic in mice. The incorporation of Freund's complete adjuvant increased the immunogenicity of the 40santigens in chickens. The 40pantigens induced greater frequencies of serological responses in chickens than the 40santigens as detected by counterimmunoelectrophoresis and immunodiffusion. This suggested that the increased protection associated with the 40pantigens may have been the result of better antibody response. The toxicity of all the fractions was evaluated by determination of lethality for 10-day-old chicken embryos because of the sensitivity and reliability of the test. The 40pfraction had an LD50 = 0.38 μg, and the 40sfraction had an LD50 = 2.5 μg. Since the 40sfraction contained no detectable LPS, it is likely that two toxins are present, one which contains LPS and one which does not.

ISSN:0008-4166    

DOI:10.1139/m82-182

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Surface microlayer phytoplankton populations were monitored to assess natural temporal and spatial variability. Microlayer samples (collected using glass plates) were compared with reference bulkwater samples over hourly, diel, and seasonal time periods on spatial scales of ~0.5 to 20 km. Microlayers were consistently depleted in chlorophyllarelative to bulkwaters in diurnal samples. Depletions had no seasonal patterns and were not influenced by dissolved nutrients or organic materials or by varying wave states. A diel pattern, with nocturnal enrichments, indicated photoinhibition of microlayer microbiota. Exceptions to these patterns occurred in naturally slicked surfaces which generally had large chlorophyllaenrichments. Disparate descriptions of microlayer phytoplankton populations in previous work probably resulted from (1) use of different sampling methods, (2) geographic variations in bulkwater phytoplankton biomass, (3) low numbers of samples, and (4) uncertain identification or definition of slick conditions.

ISSN:0008-4166    

DOI:10.1139/m82-183

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Eugenol and vanillin were examined forin vitroantifungal activity against the medically important yeasts,Candida albicansandCryptococcus neoformans. Minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC) were determined for each compound against 31 strains ofC.albicansand 33 strains ofC.neoformans. With eugenol, the mean MIC's forC.albicansandC.neoformanswere 625 and 293 μg/mL, respectively, while the mean MFC's were 1209 and 521 μg/mL, respectively. With vanillin, the mean MIC's forC.albicansandC.neoformanswere 1250 and 738 μg/mL, respectively, while the mean MFC's were 5000 and 1761 μg/mL, respectively. WithC.albicans, inhibition and retardation of growth were similar for yeast and mycelial forms, but germ tube formation was inhibited at concentrations lower than those which inhibited growth. Short-term toxicity tests with mice using the intraperitoneal route gave maximum tolerated doses of 62.5 mg/kg for eugenol and 125 mg/kg for vanillin and excluded their use as therapeutic agents for systemic mycoses.

ISSN:0008-4166    

DOI:10.1139/m82-184

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Using mutants ofBacillus subtilisthat are able to sporulate in the presence of relatively high concentrations of various carbon sources, catabolite resistance mutations were mapped by PBS1 transduction and transformation. Catabolite resistance mutations were localized at six different loci on the chromosome ofB.subtilis. The map positions of our mutants suggest that they are distinct fromsacUh,catA, andscoCreported by other investigators. Relations between our findings and initiation of sporulation have been discussed.

ISSN:0008-4166    

DOI:10.1139/m82-185

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Laboratory cultures ofTrichoderma hamatumproduce metabolites that are characterized by an isocyanide functionality. Three such metabolites predominate. One is the known compound trichoviridin (I). The other two, described here for the first time, are 3-(3-isocyano-6-oxabicyclo[3,1,0]hex-2-en-5-yl)acrylic acid (II) and a very unstable compound 3-(3-isocyanocyclopent-2-enylidene-)propionic acid (III). Production of these three metabolites by a random sample of wild isolates of the fungus has been examined. At least one of these isocyanides was isolated from all cultures in which the culture broth inhibited the growth ofMicrococcus luteus. The relative amounts of the three isocyanides produced by individual isolates were not the same and cultures were found in which I, II, or III was the main product. The isocyanide III was produced by all wild isolates which had antibiotic activity in their culture broth, and it was present in the concentration range 2–40 mg∙L−

ISSN:0008-4166    

DOI:10.1139/m82-186

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Samples of seawater, sediment, and the following invertebrates were collected from the Mediterranean Sea in the neighborhood of Alexandria, Egypt: sea urchins (Echinusspp.), clams (Tapesspp.), and wedge shells (Donax trunculus). A total of 165 samples were collected from November 1979 to July 1980. Average counts (per 100 mL or 100 g) ofVibrio parahaemolyticuscontent were as follows: seawater, 36; sea urchins, 349; sediment, 436; wedge shells, 534; clams, 1872. Samples collected in the summer months contained higher levels ofV.parahaemolyticusthan winter samples.

ISSN:0008-4166    

DOI:10.1139/m82-187

出版商:NRC Research Press    

年代:1982

数据来源: NRC