摘要:

The prevalence of specific arginine biosynthesis gene defects was studied for 319 arginine-requiring clinical isolates ofNeisseria gonorrhoeaeby using the ability of the strains to utilize intermediates of arginine biosynthesis. Only 11 % of the uracil-requiring strains defective in the carbamylation of ornithine to yield citrulline had a defective carbamoylphosphate synthetase gene (carAB). Strains defective incarABwere of auxotype CUH. The other strains (89%) having a dual requirement for citrulline and uracil, which were mostly of auxotype PCU, were defective in the ornithine transcarbamoylase gene (argF). Over 90% of the strains were defective either inargJ(174 strains) or inargF(126 strains). Three argininosuccinate-requiring strains (i.e., defective inargG) of auxotype PAU were identified. Some of the arginine auxotrophs ofN.gonorrhoeaedefective incarAB,argJ,argF, orargGwere complemented by genetic transformation with DNA from recombinant bacteriophages carrying characterized gonococcal arginine biosynthesis genes. Gene defects inproA(five strains) and inproB(six strains) were identified by gonococcal transformation assays with recombinant bacteriophages or plasmids carrying proline biosynthesis genes fromN.gonorrhoeae. None of the 11 proline-requiring strains tested was defective inproC.Key words:Neisseria gonorrhoeae, arginine biosynthesis, proline biosynthesis, gene defect, marker rescue.

ISSN:0008-4166    

DOI:10.1139/m89-179

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Results on the kinetics of 7α-hydroxysteroid dehydrogenase 7α-HSDHshowed that this enzyme could oxidize all bile acids having an –OH group at the C-7 position. Lineweaver-Burk plots showed Michaelis constant (Km) values of 0.83 and 0.12 mM for cholic acid and chenodeoxycholic acid, respectively. The effect of enzyme concentration on the reaction velocity showed a constant increase in the enzyme activity with increase in enzyme-protein concentration. 7α-HSDHwas activated by Na+, K+, Ca2+, and Mn2+ions and by reducing agents having a thiol group (dithiothreitol, 2-mercaptoethanol). Co2+, Hg2+, Fe3+, Mg2+, Zn2+, Ba2+, and Cu2+ions, chelating agents (potassium oxalate, heparin,EDTA), oxidizing agents (sodium perchlorate, sodium periodate, sodium persulphate), and detergents (Tween 20, Tween 40, Tween 80, Triton X-100, sodium lauryl sulphate) were inhibitory to 7α-HSDHactivity.Key words: 7α-hydroxysteroid dehydrogenase, bile acids, NAD+,Escherichia coli080, enzyme kinetics.

ISSN:0008-4166    

DOI:10.1139/m89-180

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The surfaces of flocculent and nonflocculent yeast cells have been examined by electron microscopy. Nonextractive preparative procedures for scanning electron microscopy allow comparison in which sharp or softened images of surface details (scars, etc.) are the criteria for relative abundance of flocculum material. Asexually flocculent budding-yeast cells cannot be distinguished from nonflocculent budding-yeast cells in scanning electron micrographs because the scar details of both are well resolved, being hard and sharp. On the other hand, flocculent fission-yeast cells are readily distinguished from nonflocculent cells because fission scars are mostly soft or obscured on flocculent cells, but sharp on nonflocculent cells. Sexually and asexually flocculent fission-yeast cells cannot be distinguished from one another as both are heavily clad in "mucilaginous" or "hairy" coverings. Examination of lightly extracted and heavily extracted flocculent fission-yeast cells by transmission electron microscopy provides micrographs consistent with the scanning electron micrographs.Key words: flocculation, budding yeast, fission yeast, scanning, transmission.

ISSN:0008-4166    

DOI:10.1139/m89-181

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Serum-free medium LD59 was used for primary isolation ofSpiroplasma kunkelii(corn stunt spiroplasma) from diseased corn plants from Mississippi. Several strains were cloned in triplicate from one primary pure culture. Some of the strains were helical in cell shape, some were nonhelical, and some were partially helical, consisting of helical and nonhelical regions in the same cell. All helical strains except one (strain I-15) exhibited flexional and rotational motility in broth culture. Partially helical strains exhibited rotational movement in helical regions only. Nonhelical cells exhibited only flexional motility. These three morphological types produced three colony types on medium LD59 solidified with 0.8% agar. Nonhelical strains produced minute "fried egg" colonies (≤ 0.2 mm in diameter after 20 days incubation), while partially helical strains produced small colonies with granular centers surrounded by satellite colonies. Strains with normal helicity in general produced large, uniformly diffuse colonies (up to 2 mm), but one helical strain (I-15) appeared to be nonmotile in broth culture and to exhibit little translational motility in agar medium, accounting for development of minute granular colonies (about 0.2 mm in diameter). All new strains were serologically closely related to known strains ofS.kunkelii, but polyacrylamide gel electrophoresis analysis of membrane proteins revealed minor differences. This is the first report of nonhelical strains ofS.kunkeliiand of helical strains with apparent impairment in translational motility.Key words:Spiroplasma kunkelii, nonhelical spiroplasmas, Mollicutes.

ISSN:0008-4166    

DOI:10.1139/m89-182

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Serum-free media that contained bovine serum albumin and lipids (fatty acids, cholesterol, phosphatidic acid, and phospholipids) to replace serum were formulated for the culture of some fastidious strains of corn stunt spiroplasma,Spiroplasma kunkelii. These media also supported good growth of other spiroplasmas, including epiphytic, entomopathogenic, and phytopathogenic strains. The growth rates attained in these serum-free media were comparable to those in media which contained serum. The serum-free broth and agar media were of major importance for culture of several fastidious strains of corn stunt spiroplasma because the serum-containing media supported little, if any, of their growth. Colonies of these fastidious strains were readily formed on serum-free agar media in aerobic, candle jar, and anaerobic environments, but were not readily formed on the serum-containing media. The serum-free media were less subject to deterioration during storage or incubation, and the growth-supporting capacity of serum-free media diminished more slowly than that of serum-containing media.Key words:Spiroplasma kunkelii,Spiroplasma citri, Mollicutes,Mycoplasmaspp. culture, entomopathogens.

ISSN:0008-4166    

DOI:10.1139/m89-183

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The hypothesis of positive interactions betweenFrancisella tularensisLVS (live vaccine strain) andAcanthamoeba palestinensiswas tested. Pregrowth of the amoebae, in a rich (autoclaved and filtered) medium, from which they were subsequently removed by filtration, conditioned the medium so that growth of the live vaccine strain ofF.tularensisoccurred and the growth rate of one other strain was increased.Key words: preconditioning of substrate, growth, survival.

ISSN:0008-4166    

DOI:10.1139/m89-184

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Soil enrichment cultures were prepared by repeated additions of methyl parathion to flooded alluvial and laterite soils incubated at 35 °C. These cultures were tested for their ability to degrade methyl parathion in a mineral salts medium in the presence and absence of yeast extract. Addition of yeast extract (0.05% w/v) accelerated the degradation of methyl parathion by both enriched cultures. Methyl parathion was degraded by the enrichment culture from alluvial soil essentially by hydrolysis in the absence of yeast extract and by nitro group reduction in its presence. The enrichment culture from laterite soil degraded methyl parathion (by hydrolysis) only in the presence of yeast extract. ABacillussp., isolated from laterite soil, degraded methyl parathion essentially by hydrolysis in the presence of a concentration (w/v) of yeast extract of 0.05%, by both hydrolysis and nitro group reduction at 0.1 and 0.25%, and exclusively by nitro group reduction at 0.5%. A similar trend was also noticed with parathion. However, fenitrothion was degraded byBacillussp. mainly by hydrolysis at all concentrations of yeast extract, whereas diazinon was not degraded.Key words: organophosphorothioates, biodegradation, yeast extract dependent pathway.

ISSN:0008-4166    

DOI:10.1139/m89-185

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

When the level of dissolved oxygen was increased to saturation in defined media fermentations ofStreptomyces clavuligerus, the total duration of activity of the penicillin ring cyclization enzyme, isopenicillin N synthase (IPNS), was extended by at least 20 h; however, no increase in the stability of the ring expansion enzyme, desacetoxycephalosporin C synthase (DAOCS), was observed. Consequently, the conversion of the excreted intermediate penicillin N to cephamycin C was 15–20% less efficient at this high oxygen concentration. The increased dissolved oxygen level also led to the complete loss ofIPNSandDAOCSactivities for 4 h during the period of fastest growth, and the rate of specific cephamycin C production fell to zero. A several hundred fold increase in the level of iron in the defined media resulted in a sixfold improvement in the rate of specific cephamycin C production after 60 h fermentation. This increased rate appeared to be due to an elevation in thein vivoactivities of a number of the cephamycin biosynthetic enzymes, particularly those catalysing later pathway steps.Key words:Streptomyces clavuligerus, isopenicillin N synthase, desacetoxycephalosporin C synthase, oxygen, iron.

ISSN:0008-4166    

DOI:10.1139/m89-186

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Ultrastructural examination of free and calcium alginate immobilizedGibberella fujikuroimycelia showed that in addition to the changes occurring during the transition phase from primary to secondary metabolism, there are several alterations in the ultrastructure of hyphae as a response to microenvironmental changes owing to immobilization constraints. Internal changes included (i) the presence of large glyoxisomelike bodies and of active vesicle-generating systems, which appeared as cloudy structures in electron micrographs; (ii) the formation of endocells, resulting in hyphae with up to three cell walls and the concomitant accumulation of secondary metabolites, mainly pigments, in peripheral cell compartments; and (iii) the progressive development of autophagic vacuoles involved in the turnover of cell constituents.Key words:Gibberella fujikuroi, immobilized fungi, alginate entrapment, ultrastructure modification, immobilization.

ISSN:0008-4166    

DOI:10.1139/m89-187

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The effect of inoculum density on preemergence disease incidence was described by linear regression. Variations in virulence among 10 isolates formed a continuum. The effect of inoculum density on hypocotyl disease incidence was described by a limiting site model and variations in virulence among the isolates also formed a continuum. The ability of an isolate to cause preemergence disease was not necessarily related to its ability to cause hypocotyl disease. Both saprophytic colonization and preemergence infection arose from propagules in the spermosphere, while depending on the isolate, infection of hypocotyls was from propagules in either the rhizosphere or the rhizoplane. The observed number of hypocotyl lesions was greater than that estimated from the percentage of plants infected. This effect was more pronounced when seeds were sown at 4 than at 1 cm depth.Key words: beans, epidemiology,Phaseolusvulgaris,Rhizoctonia solani.

ISSN:0008-4166    

DOI:10.1139/m89-188

出版商:NRC Research Press    

年代:1989

数据来源: NRC