摘要:

The host–parasite interface separating the haustorium ofErysiphe graminisand the cytoplasm of the barley epidermal cell is an invaginated portion of the host plasmalemma which becomes thicker, more osmophilic, highly invaginated toward the haustorium, and which loses its transparent central stratum. This extrahaustorial membrane is always 1–4 μm distant from the haustorial wall and at first is covered with a thin layer of normal cytoplasm. Later, the host cytoplasm greatly increases in volume, becomes much less dense, and organelles become less confined.

ISSN:0008-4166    

DOI:10.1139/m74-230

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Streptomyces lipmaniiproduces two β-lactam antibiotics, penicillin N and 7-(5-carboxyvaleramido)-7-methoxycephalosporanic acid. A method has been developed whereby mutation can be directed toward preselected markers, including some affecting antibiotic production. DNA synthesis was synchronized by amino acid starvation of a leucine auxotroph (LA 473). Double-isotope techniques using [14C]- and [3H]-thymidine provided a means of monitoring DNA synthesis. Aliquots of the synchronized culture were treated withN-methyl-N′-nitro-N-nitrosoguanidine (NTG) and plated on selective media. Mutation frequencies for each marker varied as much as 100-fold. The data were consistent with the hypothesis that NTG preferentially mutates the replicating region of DNA.

ISSN:0008-4166    

DOI:10.1139/m74-231

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Nitrate-reducing bacteria, sulfate-reducing bacteria, fluorescent bacteria, and the total viable count were enumerated in three stream systems within a high mountain watershed over a period of two winters and two summers from 1970 to 1972. Spread plate and most probable number procedures showed that the number of fluorescent bacteria, sulfate-reducing bacteria, nitrate-reducing bacteria, and the total count were generally constant throughout the year at the lowest sampling site on the stream systems. However, in some cases and for short periods of time, the numbers of these bacteria appeared to be influenced by recreational use of the land and stream flow. For example, denitrifying bacteria increased in number during the winter recreational period and gave the lowest counts in July.

ISSN:0008-4166    

DOI:10.1139/m74-232

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The effect of two environmental factors, pH and temperature, on sporulation and enterotoxin production inClostridium perfringenstype A was determined. A maximum level of enterotoxin was obtained in Duncan and Strong sporulation medium when the pH was not controlled by external addition of NaOH. Slightly lower levels were obtained when the pH was controlled at 7.0. Percentage of sporulation and heat-resistant spore population levels were similar at pH 7.0 and when the pH was not externally controlled. Enterotoxin concentration, percentage of sporulation, and heat-resistant spore levels decreased greatly when the pH was kept at 8.0, 8.5, and 6.0. At pH 5.5 vegetative growth occurred although sporulation and enterotoxin production did not. Levels of heat-resistant spores and enterotoxin were higher at 37C than at 25, 30, or 43C. Enterotoxin formation was not detected at 46C.

ISSN:0008-4166    

DOI:10.1139/m74-233

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

When 1-cm diameter, waterlogged, sandy clay loam soil aggregates were amended with 2% (w/w) cellulose or 2% (w/w) wheat straw, significant C2H2-reduction activity developed whether the aggregates were incubated under aerobic or anaerobic gas phases. The only N2-fixing bacteria which proliferated were anaerobes or facultative anaerobes. Aerobic N2-fixing bacteria did not proliferate in any of the aggregates, even though a few were initially present in the soil. The anaerobic bacteria in aerobically incubated, cellulose-amended aggregates proliferated more slowly than those in the anaerobically incubated aggregates, but eventually produced a higher maximum rate of C2H2-reduction. The activities of the N2-fixing bacteria in straw-amended aggregates were similar under both aerobic and anaerobic gas phases. High amendment levels (20% w/w) altered the soil structure and the requisite anaerobic microsites were not developed as rapidly under aerobic incubation conditions and so the onset of C2H2-reduction activity was delayed.

ISSN:0008-4166    

DOI:10.1139/m74-234

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Recovery ofSalmonellafrom low-moisture foods was studied using selective enrichment in tetrathionate brilliant green and selenite-cystine broths at 35C and 43C. A total of 1375 samples of dried dairy, soya, and rendered animal by-products were analyzed. All samples were preenriched before selective enrichment. No significant difference in recovery was detected between tetrathionate brilliant green and selenite cystine at either temperature, which is in contrast to our earlier findings with red meats. Pairing of enrichment conditions resulted in the detection of more positive samples than the use of any single enrichment condition.

ISSN:0008-4166    

DOI:10.1139/m74-235

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

A purified toxin fromMortierella wolfiicontained about 60% lipid, 39% protein, and less than 0.4% carbohydrate. Labelling of the toxin, with the protein-alkylating agent3H-iodoacetic acid and subsequent extraction of the lipid with a chloroform–ethanol–water mixture resulted in almost all of the radioactivity (97%) being present in the ethanol–water layer, suggesting that the lipid was not covalently linked to the protein. A threefold reduction in the lipid content of the toxin by ion-exchange chromatography did not reduce toxicity of the toxin, expressed in mean lethal dose (LD50) per unit of protein. The LD50for mice is 3.3 μg protein. The cumulative findings suggested that the active toxic substance is a protein, with a high proline content (17.2% w/w) and a calculated molecular weight from amino acid analysis of 22 800 daltons.

ISSN:0008-4166    

DOI:10.1139/m74-236

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Pure ascospore suspensions of three strains ofSaccharomyces cerevisiaehave been prepared by sequential treatment with 2-mercaptoethanol, Glusulase, and sonication. Light microscopy and acid-fast staining revealed the presence of only ascospores. Various germination media tested using the ascospore preparation revealed different nutritional requirements for the germination of auxotrophic and prototrophic yeast strains. Acid-fast staining of the germinating ascospores was shown to be an effective method for studying the kinetics of ascospore germination. The anaerobic nature of ascospore germination was demonstrated using this staining technique.

ISSN:0008-4166    

DOI:10.1139/m74-237

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Rocky Mountain spotted fever rickettsiae, cultivated either in yolk sacs of embryonated chicken eggs or in mouse L cells, were purified by centrifugation through a linear sucrose density gradient in a zonal rotor. Under the conditions of the experiments the rickettsiae banded at a density of about 1.21. Intact organisms with what appeared to be large translucent capsules were found in this band. The degree of purity was high because yolk sac contamination was not detected in rickettsial suspensions derived from embryonated eggs, and little extraneous material was observed by electron microscopy in suspensions obtained from either host. About 4 × 108rickettsial particles were recovered from each gram of yolk sac and 2 × 1010particles from each gram of L cells, a 50-fold difference. Each milligram dry weight of purified rickettsiae contained about 1 × 1010particles.

ISSN:0008-4166    

DOI:10.1139/m74-238

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Previously the kinetics of loss of viability of freeze-driedSerratia marcescens8UK were determined by Cox and Heckly as a function of oxygen concentration and time. Results are presented here when dehydration is brought about by aerosolization into atmospheres of low relative humidity (RH) rather than by freeze-drying. As for freeze-driedS.marcescens, oxygen was toxic and viable decay followed the same kinetics with respect to oxygen concentration and time. The influence of RH upon viable decay (which was not studied in the previous report) was that above 65% RH oxygen was not toxic but was progressively more toxic as the humidity was further reduced. Kinetic analyses of the results indicate that the site for the toxic action of oxygen lies in the interspace between the cytoplasmic membrane and the cell wall. Such a finding is consistent with other data which suggest that cell division and (or) cell wall synthesis in bacteria are inhibited by oxygen.

ISSN:0008-4166    

DOI:10.1139/m74-239

出版商:NRC Research Press    

年代:1974

数据来源: NRC