摘要:

The ability ofBacillusspp. to alter the nodulation ofPhaseolus vulgarisbyRhizobium etliwas assessed. The simultaneous presence of bothRhizobium etliTAL 182 andBacillus megateriumS49 on plant roots during the early stages of plant growth was necessary for enhanced nodulation ofPhaseolus vulgarisby theRhizobiummicrosymbiont. Coinoculation with both bacterial species also facilitated heterologous nodulation ofRhizobiumTAL 182 onPhaseolus acutifolius. These results are consistent with earlier reports of increased root hair proliferation and lateral root formation in response to coinoculation. Split-root experiments revealed that coinoculation partially suppressed host-controlled regulation of nodulation, implicating a plant interaction with the two bacterial species. Changes to the nodulation potential ofR.etlidue to coinoculation withBacillusspp. demonstrate the potential for root-associated organisms other than rhizobia to alter the dynamics of the legume–Rhizobiumsymbiosis.Key words:Bacillus, nodulation enhancement, heterologous nodulation.

ISSN:0008-4166    

DOI:10.1139/m97-001

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Coliforms andAeromonas, isolated over a sampling period of 4 years from a Swedish drinking water well, were analysed for their phenotypical diversity and for their ability to persist in the well water. From each of the 40 water samples collected from the well, 32 bacterial isolates were subjected to typing by the PhenePlate (PhP) biochemical fingerprinting system. Strains able to persist in the well water were further characterized using the API 20E system, gas–liquid chromatographic cellular fatty acid analysis, and the DNA fingerprinting technique AFLP. Using the PhP system, a total of 170 different phenotypes were identified among 1143 studied isolates. Most phenotypes were only represented by a few isolates and (or) were restricted to one or two sampling occasions. However, one particular phenotype (RV-C01), identified asAeromonas hydrophilausing the API 20E system and fatty acid analysis, reoccurred in 28 samples distributed over the whole study period and often dominated the bacterial population in the well water. AFLP analysis revealed that the RV-C01 isolates displayed basically identical fingerprints. Our results thus suggest that a genetically stableAeromonasclone resided in the well water over the whole 4-year study, whereas other bacterial strains studied were only transient inhabitants of the well.Key words:Aeromonas, coliform, water, diversity.

ISSN:0008-4166    

DOI:10.1139/m97-002

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

ARhodococcussp. 094 bacterium was tested for its ability to oxidize alkanes in crude oil emulsified by nonionic chemical and biological surfactants. Oxidation rates were measured in a 3-h period by Warburg respirometry.14CO2recovery was measured from the [1-14C]hexadecane spiked crude oil. Response to emulsified oil depended on the physiological state of the bacteria (i.e., cells harvested in the exponential and stationary growth phases) were tested. Oxidation rates by cells in the exponential growth phase were negatively affected by surfactant amendment. Oxidation rates by cells in the stationary growth phase were in some cases stimulated by surfactants. The stimulatory effect depended on both the chemical structure and the physicochemical properties (i.e., hydrophilic–lipophilic balance (HLB)) of the surfactants. Surfactants with intermediate HLB values (8–12) gave the best results. Neither the biosurfactants nor the commercial oil-spill dispersants tested had any significant stimulatory effect.Key words: biodegradation, bacteria, surfactants, crude oil, Warburg.

ISSN:0008-4166    

DOI:10.1139/m97-003

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The surface hydrophobicities of fungal spores from the entomopathogenic generaBeauveria,Metarhizium, andTolypocladiumwere quantitatively measured and compared using a novel assay employing salt-mediated aggregation and sedimentation (SAS). Spores with greater hydrophobicities were easily identified by their aggregation and sedimentation out of suspension at faster rates under lower salt concentrations. Of the three ammonium salts investigated for their salting-out potentials, ammonium sulfate gave the most pronounced effect, closely followed by ammonium chloride, and then ammonium acetate. Using the SAS assay, spores exhibited more pronounced hydrophobic properties at pH 5.8 than at higher pH values of 6.8 and 7.8. The effects of temperature and spore concentration upon the SAS assay were also investigated, with greater spore sedimentation occurring at elevated temperature. By plotting SAS values for two ammonium salt concentrations (0.01 and 0.1 M) in a coordinate system, it was possible to differentiate the hydrophobicities of all five spore isolates, clearly demonstrating the superiority of SAS over an existing phase-exclusion assay. The significance and potential of the SAS assay are also discussed.Key words: fungal spores, hydrophobicity, microassay, SAS, salting out, microbial insecticides.

ISSN:0008-4166    

DOI:10.1139/m97-004

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Survival ofSalmonella typhimuriumwithin macrophages is associated with virulence. Most data on the fate ofSalmonelladuring infection of macrophages are derived from viable counts of intracellular bacteria. These counts are a result of a combination of bacterial death and growth within the intracellular population but may not reflect the true levels of either macrophage killing ofSalmonellaor bacterial growth inside cells. In this study, two independent methods have been used to obtain a more accurate measurement of absolute levels of both death and growth ofSalmonellainside macrophages. A purine auxotroph (purD) was used to measureSalmonelladeath in the absence of bacterial growth and then bacterial growth was measured by supplementing thepurDcultures with adenosine. Numbers of dead and liveSalmonellawere also quantitated using the BacLight staining system, which distinguishes dead from live bacteria. Both methods demonstrate that killing ofSalmonellaby macrophages is considerably greater than detected using traditional cell counts and that bacterial inactivation occurs throughout the infection period.Salmonellawas inactivated at a similar rate in both J774 macrophages (most permissive macrophages) and peritoneal exuadate macrophages (least permissive macrophages), suggesting that the major difference between these cells is the ability to limit bacterial growth. These studies also demonstrate that growth ofSalmonellawithin murine macrophages occurs simultaneously with significant amounts of bacterial death. Identifying the factors responsible for shifting the interaction between macrophages and bacteria toward conditions that favor bacterial growth will be critical to understandingSalmonellavirulence.Key words:Salmonella, macrophage,purD, purine auxotroph.

ISSN:0008-4166    

DOI:10.1139/m97-005

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

DNAs from 40 strains ofPichia cactophilaandPichia norvegensis, yeasts characteristic of cactus necroses, were compared using randomly amplified polymorphic DNA (RAPD) banding patterns and killer/sensitive phenotypes. Both species belong to the same species complex within the genus. The levels of between-strain RAPD variation were high in both species (higher in the automicticP.cactophilathan in the heterothallicP.norvegensis), although there is little variation in physiological abilities within either species. Although each species was a separate lineage, RAPD analysis confirms that the species are related. Within each species, RAPD variation was related to the geographic origin of the strains.Pichia cactophilastrains from southern Florida were more related to those from Antigua than to those from northern Florida. These results correlated well with the differences among killer/sensitive phenotypes of strains. Principal component analysis indicated that the phenotypes of each species differ. Here too, strains from southern Florida were more similar to those from Antigua than to those from northern Florida. Previous work had identified differences in the cactophilic yeast communities from southern and northern Florida, and these results indicate that the differences are detectable at the population level as well.Key words: RAPD phylogeny,Pichia, killer factor.

ISSN:0008-4166    

DOI:10.1139/m97-006

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A 24-kDa protein that elicits ethylene production and necrosis in leaves of dicotyledonous plants was previously purified from culture filtrates ofFusarium oxysporumSchlechtend:Fr. f.sp.erythroxyli. Antisera to the denatured 24-kDa protein detected 2.5 ng of the 24-kDa protein on Western blots at 100 000-fold dilutions. The antisera cross-reacted with a 24-kDa protein on Western blots of culture filtrates from three otherF.oxysporumformae speciales. Of sevenFusariumspecies, onlyF.oxysporum,F.acuminatumEllis and Kellerm., andF.avenaceum(Fr.:Fr.) Sacc. isolates produced an antigenically related 24-kDa protein. Although there were differences in the profiles of proteins extracted from stems of coca (Erythroxylum cocavar.cocaL. Lam.) infected withF.oxysporumf.sp.erythroxylicompared with uninfected stems, antisera to the 24-kDa protein did not cross-react with any proteins from the infected coca stems. For the fungal isolates studied, the best medium tested for production of the 24-kDa protein contained 1% sucrose and 1% asparagine. Biological activity of theF.oxysporumculture filtrates on sweet basil leaves was consistently correlated with the presence of the 24-kDa protein. Production of the 24-kDa protein was limited in cultures containing pectin or cellulose as the primary carbon source, or in cultures lacking sucrose or casamino acids. Water-soluble extracts from coca stems inhibited production of the 24-kDa protein, whereas cellulose and pectin did not. Components produced by the plant may limit production of the 24-kDa protein in infected plant tissue and thereby limit the response of the plant to the fungus. These results suggest the 24-kDa protein does not function in the symptomatic phase of theF.oxysporumf.sp.erythroxyli–coca disease interaction.Key words:Fusarium oxysporum, toxin, elicitor.

ISSN:0008-4166    

DOI:10.1139/m97-007

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Aspergillus tamariiwas able to produce biomass in media containing β-methylD-xyloside, a synthetic analogue of xylobiose, as the only carbon source. β-MethylD-xyloside was a more effective inducer than xylan at the same concentration for xylanase and β-xylosidase activities. The delayed consumption of β-methylD-xyloside byA.tamariicells suggests the requirement of a specific inducible transport system and a slow metabolic process. The synthesis of this transport system was probably repressed by the presence of easily metabolizable sugars. β-MethylD-xyloside was hydrolyzed to xylose by an intracellular β-xylosidase.Key words: xyanolytic microorganisms, xylanase, β-xylosidase,Aspergillus tamarii.

ISSN:0008-4166    

DOI:10.1139/m97-008

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Promoter-like sequences from the chromosomal DNA of thermophilic strainLactobacillus acidophilusATCC 4356 were cloned. Analysis of the three DNA fragments showing promoter activity, designated P3, P6, and P15, were performed inLactobacillus reuteri,Lactococcus lactis, andE.coli. The reportercat-86gene was expressed in all three bacterial species under control of the fragments P3 and P6. Fragment P15 showed promoter activity only inLactobacillus reuteriandE.colibut not inLactococcus lactis. The three host-specific transcriptional start points (TSPs) were used when transcription of thecat-86gene was controlled by fragment P3 inLactobacillus reuteri,E.coli, andLactococcus lactis. Similarly, fragment P15 initiated transcription of thecat-86gene at two distinctive sites inLactobacillus reuteriandE.coli. Only within fragment P6, a common TSP was used inLactobacillus reuteriandE.coli, but different from that used inLactococcus lactis. Each TSP was preceded by the putative −35 and −10 hexamers. Computer analysis of the fragment P3 sequence revealed the existence of divergent promoterlike sequence (P3rev) located on the complementary DNA strand. Fragments P6 and P15 were also functional inLactobacillus acidophilusATCC 4356 from which chromosomal DNA they were originally cloned.Key words:Lactobacillus acidophilus, promoter-like sequences, regulation.

ISSN:0008-4166    

DOI:10.1139/m97-009

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The relationship among membrane fatty acid composition, membrane fluidity, and stress tolerance was investigated in yeast cells. Several strains were examined for their ability to survive heat, ethanol, and hydrogen peroxide stresses. Membrane fluidity was determined by measuring fluorescence anisotropy using diphenylhexatriene as a probe. There was no obvious relationship among membrane fatty acyl composition, membrane fluidity, and stress tolerance in the strains examined. A consistent trend in the present study was an observed decrease in membrane fluidity following thermal treatment, which coincided with a reduction in cell viability. We suggest that protein denaturation may be responsible for the observed effect of elevated temperature on membrane fluidity and viability. This was implied by observations on the irreversible nature of thermal transitions, as measured by breaks in Arrhenius plots, in which stationary phase cells were shown to exhibit higher transition temperatures (53.9–55.5 °C) than exponential phase cells (49.5–51 °C). Furthermore, the thermal transition temperature was shown to increase in exponential phase cells following heat shock, which was associated with an increase in thermotolerance. We suggest that the thermotolerant state of heat-shocked cells and cells entering stationary phase may be associated with increased protein stability. However, despite the relatively good correlation between thermal transition temperature and stress tolerance, the thermal transition temperature did not predict the stress tolerance of a given strain, as stress-sensitive strains had similar transition temperatures to those of stress-resistant strains.Key words: membrane fluidity, stress tolerance, yeast, membrane lipids.

ISSN:0008-4166    

DOI:10.1139/m97-010

出版商:NRC Research Press    

年代:1997

数据来源: NRC