摘要:

We determined whether Arg13, Met31, and Ser95 of the heat-labile enterotoxin B subunit (LT-B) might be involved in Lt-B binding to oligosaccharides, which did not bind to the B subunit of the cholera toxin (CT-B). Three LT-B mutants, R13H, M31L, and S95A were prepared by substituting three amino acid residues that differ in CT-B. These mutants formed a pentamer and exhibited the same binding ability to the GM1ganglioside as native LT-B. Although these mutants did not bind to Bio-Gel A-5m, they did bind to the glycoprotein from mouse intestinal cells in the order R13H > M31L > S95A. These data suggest that Ser95, Met31, and Arg13 are important for LT-B binding to Bio-Gel A-5m, and that although Ser95 is also partially responsible for LT-B binding to the glycoprotein, Arg13 has no significant involvement in it.Key words: heat-labile enterotoxin, cholera toxin, Bio-Gel A-5m, glycoprotein.

ISSN:0008-4166    

DOI:10.1139/m96-127

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A numerical study of the fatty acid patterns of 263 reference strains belonging to the generaArthrobacter,Aureobacterium,Brevibacterium,Cellulomonas,Clavibacter,Corynebacterium,Curtobacterium,Erysipelothrix,Microbacterium, andRhodococcuswas undertaken based on cultural and chemical standardized techniques. Clustering was by the unweighted pair group method using the correlation coefficient. Two cluster groups could be defined at the 62% level, one containing strains characterized by saturated and monounsaturated fatty acids and the second group characterized by iso- and anteiso-branched fatty acids. Within the first cluster group, a clear separation of strains assigned to the generaRhodococcus,Erysipelothrix, andCorynebacteriumcould be achieved. Furthermore, strains of the speciesCorynebacterium glutamicum,Corynebacterium ammoniagenes,Corynebacterium diphtheriae, 'Corynebacterium ulcerans,' andErysipelothrix rhusiopathiaecould be found in distinct clusters, based on quantitative differences in fatty acid patterns. Within the second cluster group, a high degree of similarity between the generaAureobacterium,Cellulomonas,Clavibacter,Curtobacterium, andMicrobacteriumfound in phylogenetically based studies could be shown also by fatty acid patterns. Several strains of the plant pathogenic coryneform bacteria assigned to the genusClavibacterandCurtobacterium flaccumfacienswere found within one cluster, indicating a high similarity between these genera. Strains of the genusArthrobacterwere grouped into three adjacent clusters and could not be differentiated by fatty acid patterns. The results of the study are essentially in line with a previously published numerical survey and with other chemotaxonomic and genetic data. Thus, quantitative fatty acid patterns are recommended for identification of several coryneform bacterial genera. In some cases an identification at the species level is possible.Key words: fatty acid analysis, coryneform bacteria, differentiation, numerical analysis.

ISSN:0008-4166    

DOI:10.1139/m96-128

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Twenty-twoBacillusspp. isolates from the rhizosphere ofPhaseolus vulgaris'Contender' were identified using Biolog™, gas chromatographic fatty acid methyl ester, and 23S rDNA analyses. Some of theBacillusisolates produced significant amounts of the phytohormone indoleacetic acid (IAA) when grown in a liquid culture medium supplemented with 100 μgL-tryptophan/L; less IAA was produced in culture medium not supplemented withL-tryptophan. Thin-layer chromatography, high-performance liquid chromatography, gas chromatography – mass spectrometry, and the avena coleoptile bioassay were used to identify and quantify IAA produced byBacillusisolates. Significant differences were observed in the amounts of IAA produced by different strains ofBacillus, with amounts varying from 0.40 to 4.88 μg/mL. α-Methyltryptophan-resistant mutants ofBacillusexhibited altered IAA production and excreted tryptophan into the growing medium. The IAA-producingBacillusisolates promoted root growth and (or) nodulation when coinoculated withRhizobium etli(TAL 182) onPhaseolus vulgaris'Contender' under gnotobiotic conditions in growth chambers. Coinoculation resulted in increased nodule number, nodule fresh weight, nitrogenase activity, leghemoglobin content, and total soluble protein content in the root nodules ofPhaseolus vulgaris. In contrast, coinoculation with α-methyltryptophan mutants resulted in decreased nodulation, indicating thatBacillusisolates have a direct effect on either theRhizobiumor the plant and the effect may not be singularly attributed to their ability to produce IAA in vitro.Key words:Bacillus, indoleacetic acid production, nodulation enhancement.

ISSN:0008-4166    

DOI:10.1139/m96-129

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A number of bacteria and their phages were isolated from a saltern near Alicante, Spain. One isolate,VibrioB1, a moderate halophile that is probably a strain ofVibrio costicola, was host to a lytic phage, UTAK. Studies of the host bacterium included the effects of salt concentrations on the action of a number of inhibitory agents. Phage UTAK has a head, a tail, and a baseplate. It contains 80 kbp of double-stranded DNA with no unusual bases. It was stable for long periods in the absence of high salt concentrations and even in distilled water. Salt concentrations had little effect on adsorption of UTAK to its host but resulted in considerable changes in burst size. It appears that phages of halophilic and salt-tolerant eubacteria, and also of some marine bacteria, have much lower salt requirements for stability than the phages of halophilic archaebacteria. Our results suggest that ionic controls of phage replication in these eubacteria may differ from those of growth.Key words: halophiles,Vibriosp., bacteriophage, salt responses.

ISSN:0008-4166    

DOI:10.1139/m96-130

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Clinical isolates ofStaphylococcus aureuswere found to exhibit strain-specific heterogeneity to the growth-enhancing effects of human urokinase (UK), a proteinase with plasminogen activator activity. Nine out of fourteen (64%) methicillin-sensitive strains ofS.aureuswere responsive to UK in "in vitro" cultures. In contrast, 3/29 (10%) methicillin-resistant strains were responsive to the proteinase. When only strains isolated from western Canada were considered, 6/11 methicillin-sensitive strains and 1/26 methicillin-resistant strains were responsive to UK. The single western Canadian methicillin-resistant strain (strain 456) responsive to UK was one of two isolated from the same patient, indicating that the two strains were phenotypically different. Strain 456, resistant to 32 μg mefhicillin/mL, was responsive to as little as 50 U UK/mL and enhancement of growth was evident by 9 h of incubation at 37 °C. This growth enhancement was specific to UK and not duplicated by equivalent concentrations of other proteins (bovine serum albumin, trypsin, plasminogen). The results presented indicate differences in the frequency of the UK-responsive phenotype between methicillin-sensitive and -resistantS.aureus. These findings indicate that the UK phenotype ofS.aureusmay have utility in both phenotyping clinical isolates, as well as providing insights into the regulation of growth in this clinically important organism.Key words:Staphylococcus aureus, growth, urokinase, methicillin resistance.

ISSN:0008-4166    

DOI:10.1139/m96-131

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Microsclerotia of the bioherbicidal fungusColletotrichum truncatumwere produced in submerged culture. Seedlings of the weedSesbania exaltatabecame infected when seeds were germinated in air-steam pasteurized (60 °C, 30 min) field soil infested with 165 microsclerotia/cm3. Infection was first noted 3 days after planting seeds, when the pathogen was recovered from 5% of plant segments taken from within 0.5 cm of the soil surface. By day 7,C.truncatumwas recovered from 38% of stem and root segments within 0.5 cm of the soil surface, and from 60% of similar segments by day 8. Of all pathogen recovery, 66% came from segments within 0.5 cm of the soil surface and 92% of recoveries came from within 1.0 cm of the soil surface. All freshly produced microsclerotia on Nobel water agar had germinated after 24 h and conidial production from germinated microsclerotia was detected. Conidiation peaked in vitro after 2 days, with approximately 3500 conidia being produced per microsclerotium. In situ, light microscopy showed that about 40% of microsclerotia produce setae after 1 day in pasteurized potting mix. This level was virtually unchanged after 2, 3, and 4 days of incubation though all microsclerotia remained viable. Scanning electron microscopy determined that, in situ, microsclerotia germinated sporogenically to produce conidia and setae. Newly produced conidia germinated and formed appressoria onS.exaltataroots after 2 days, when root radicles were less than 1 day old.Key words:Colletotrichum truncatum,Sesbania exaltata, bioherbicide, mycoherbicide, microsclerotia.

ISSN:0008-4166    

DOI:10.1139/m96-132

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

β-1,3-Glucanases are produced byTrichoderma harzianumwhen it is grown in the presence of chitin or isolated cell wall from fungi. An endo-β-1,3-glucanase from the culture filtrate ofT.harzianumwas purified by gel filtration on Sephacryl S-200, followed by hydrophobic interaction chromatography on phenyl-Sepharose. A typical procedure provided 134-fold purification with a 3.6% yield. The molecular mass of the purified endo-β-1,3-glucanase was found to be approximately 36 kDa, as estimated by sodium dodecyl sulfate – polyacrylamide gel electrophoresis on a 10% w/v slab gel. The enzyme was active toward glucans containing β-1,3-linkages and hydrolysed laminarin to form oligosaccharides. TheKmandVmaxvalues for β-1,3-ghicanases, using laminarin as substrate, was 1.18 mg∙mL−1and 1.26 U∙mL−1, respectively. The pH optimum for the enzyme was pH 4.4 and maximum activity was obtained at 45–50 °C. Enzyme activity was strongly inhibited in the presence of HgCl2and stimulated by cations such as Zn2+and Ca2+.Key words: endo-β-1,3-glucanase,Trichoderma harzianum, purification, characterizat

ISSN:0008-4166    

DOI:10.1139/m96-133

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The effects of water activity (aw, 0.994–0.85 = 0.4–21.0 (−)MPa water potential), temperature (5–42 °C), and their interactions on microconidial germination of three isolates each ofFusarium moniliformeandFusarium proliferatumwere determined in vitro on a maize meal extract medium. Temporal germination rates of microconidia of isolates of both species were significantly influenced by bothawand temperature. Germination was very rapid at >0.94awwith an almost linear increase with time. Germination rates of microconidia ofF.moniliformewere slower than those ofF.proliferatumisolates at marginalawlevels and 5–25 °C, while at higher temperature (30–37 °C), the former germinated more rapidly than the latter. Theawminima for germination of isolates of both species was 0.88, with none occurring at 0.85awover a 40-day incubation period. At 37 °C, isolates ofF.moniliformehad slightly lowerawminima than those ofF.proliferatum. The narrowest range ofawfor germination was at 5 °C, and none occurred at 42 °C. The effect ofaw× temperature interactions on the lag phases (h) prior to germination and the germination rates (h−1) were estimated using the Gompertz model and the Zwietering equation. This showed that lag phases were shorter at 25–30 °C and 0.994–0.98aw, and were increased to 10–500 h at marginal temperatures (5–10 °C) forF.proliferatumand longer forF.moniliforme. At marginalawlevels (0.92–0.90), lag times were increased to >250 h. Germination rates (h−1) were different for the two species. Microconidia ofF.moniliformegerminated optimally at 25–37 °C and 0.96–0.98aw, but this changed to 30 °C at 0.90–0.94aw, while germination of microconidia ofF.proliferatumremained optimum at 30 °C, regardless ofaw. There were statistically significant (P < 0.01) effects ofaw, temperature, isolate, and two- and three-way interactions forF.proliferatum, but there were no intraisolate effects forF.moniliforme. The ecological significance of these data for understanding colonization patterns of these important fumonisin-producing fungi are discussed.Key words: water activity, temperature, germination, fumonisin producing,Fusariumspp.

ISSN:0008-4166    

DOI:10.1139/m96-134

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Degradation of dicyclopentadiene (DCPD) to carbon dioxide and oxygenated intermediates was established in the laboratory. Screening of many inocula using BIOLOG™ MT plates showed that no single colony isolate readily mineralized DCPD. Mixed cultures from a variety of environmental sources produced14CO2when incubated with [14C]DCPD, but most of the DCPD was metabolized to oxygenated intermediates that could be extracted from the culture liquid and detected using gas chromatography and mass spectroscopy. Stimulation of environmental inocula with nutrients and preexposure to DCPD before testing for degradation gave mineralization rates after 25 days of in vitro incubation that were twice as fast as those previously reported.Key words: dicyclopentadiene, bioremediation, microbial community, GC–MS, biometer flask.

ISSN:0008-4166    

DOI:10.1139/m96-135

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The use of 16S rRNA targeted gene probes for the direct analysis of microbial communities has revolutionized the field of microbial ecology, yet a comprehensive approach for the design of such probes does not exist. The development of 16S rRNA targeted oligonucleotide probes for use with fluorescence in situ hybridization (FISH) procedures has been especially difficult as a result of the complex nature of the rRNA target molecule. In this study a systematic comparison of 16S rRNA targeted oligonucleotide gene probes was conducted to determine if target location influences the hybridization efficiency of oligonucleotide probes when used with in situ hybridization protocols for the detection of whole microbial cells. Five unique universal 12-mer oligonucleotide sequences, located at different regions of the 16S rRNA molecule, were identified by a computer-aided sequence analysis of over 1000 partial and complete 16S rRNA sequences. The complements of these oligomeric sequences were chemically synthesized for use as probes and end labeled with either [γ-32P] ATP or the fluorescent molecule tetramethylrhodamine-5/-6. Hybridization sensitivity for each of the probes was determined by hybridization to heat-denatured RNA immobilized on blots or to formaldehyde fixed whole cells. All of the probes hybridized with equal efficiency to denatured RNA. However, the probes exhibited a wide range of sensitivity (from none to very strong) when hybridized with whole cells using a previously developed FISH procedure. Differential hybridization efficiencies against whole cells could not be attributed to cell wall type, since the relative probe efficiency was preserved when either Gram-negative or -positive cells were used. These studies represent one of the first attempts to systematically define criteria for 16S rRNA targeted probe design for use against whole cells and establish target site location as a critical parameter in probe design.Key words: 16S rRNA, oligonucleotide probes, in situ hybridization.

ISSN:0008-4166    

DOI:10.1139/m96-136

出版商:NRC Research Press    

年代:1996

数据来源: NRC