摘要:

A degradative microbial consortium consisting of at least nine bacterial and one algal species was isolated from soil with diclofop methyl as the sole carbon source. In continuous flow culture, the presence of the algae increased diclofop methyl degradation and removal by 36%. Batch culture experiments with14C-labeled diclofop methyl confirmed algal involvement in the mineralization of diclofop methyl as there was no significant difference in the amount of14CO2evolved by the bacterial consortium with and without the algal activity when the consortium was cultivated in the dark to inhibit algal growth, while 11% more14CO2was produced in the light by the algal–bacterial consortium. Pure cultures isolated from the bacterial consortium could not individually mineralize diclofop methyl as the sole carbon source. However, when supplied with an additional carbon source, two strains could mineralize diclofop methyl. Addition of either the complex growth medium, or a cell-free filtrate from the algal–bacterial consortium to batch systems containing14C-labeled diclofop methyl resulted in a significant increase in the production of14CO2by the bacterial consortium, suggesting co-metabolism of diclofop methyl in the presence of a labile carbon source. Removal of diclofop methyl by the bacterial consortium was increased by 36% when a larger surface to volume ratio was provided by glass beads that allowed extensive biofilm formation. The requirement for exogenous carbon sources and the inability of isolated pure cultures to degrade diclofop methyl indicated that interspecies interactions are necessary for degradation. The positive effect of sessile growth suggested that spatial organization of cells may also be important for degradation.Key words: consortium, degradation, herbicide, microbial interactions.

ISSN:0008-4166    

DOI:10.1139/m94-055

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A total of 108Escherichia colistrains characterized as enteropathogenic (EPEC) by serotyping and the presence of EPEC adherence factor (EAF) sequences were examined for cytotoxin production by cell line assays and colony hybridization with Shiga-like toxin (SLT) probes. Cytolethal distending toxin (CLDT) production was found in three (2.8%) strains belonging to serotype 086:H34, while one O11 lab:NM strain hybridized with a SLT-II probe but did not express any cytotoxic activity. All four strains showed localized adherence to HeLa cells and hybridized to anE.coliattaching–effacing gene (eae) probe. The CLDT-producing strains had multiple plasmids and some were present in all strains, including a plasmid of ~54 MDa that hybridized with the EAF probe.Key words: enteropathogenicEscherichia coli, EPEC adherence factor sequences, Shiga-like toxin, cytolethal distending toxin.

ISSN:0008-4166    

DOI:10.1139/m94-056

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The diversity of 16 strains of chickpea-infective rhizobia from various geographical origins was analysed using genotypic and phenotypic approaches. Multilocus enzyme electrophoresis was performed, and restriction fragment length polymorphisms of the amplified 16S+IGS (intergenic spacer) rRNA gene, assimilation of 147 carbon sources, antibiotic resistance, and tolerance to NaCl and extreme pH values and temperatures were tested. These approaches had different discriminating powers. Esterase polymorphisms gave a unique pattern for each strain, allowing this method to be used for strain fingerprinting. Genetic distances between strains were estimated. The three approaches used in this study yielded consistent results. They evidenced high heterogeneity among the strains, and made it possible to classify the strains into two clusters. Isozyme patterns for superoxide dismutase were particularly interesting, since they delineated the same two groups. The phenotypic tests clearly confirmed the existence of two genetic groups on the basis of 11 phenotypic characters. Owing to the large phylogenetic distance between the two groups of strains, the taxonomic status of chickpea-infective strains is discussed.Key words:Rhizobiumsp. (Cicer arietinumL.), genetic diversity, multilocus enzyme electrophoresis, restriction fragment length polymorphisms, phenotypic diversity.

ISSN:0008-4166    

DOI:10.1139/m94-057

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Numerical analysis was used to characterize 111Vibrionaceaestrains. These included 31 reference cultures belonging to the generaAeromonas,Listonella, andVibrioand 80 strains isolated from the seasonally cold coastal waters of Newfoundland. The sources of the regional strains were the brown algaAlaria esculentaand the giant scallopPlacopecten magellanicus. Most of the regional strains grew at temperatures associated with psychrotrophs, while a small proportion may have been psychrophilic. All of the regional strains grew at 4 °C. A routine incubation temperature of 20 °C was chosen and in tests for utilization of organic components as sole sources of carbon and energy the strains were incubated for 3 weeks rather than the more common 6-day period. The treatment of weak positive results as weak positive, positive, or negative was investigated and it was decided that the general conclusions reached in the study would not be significantly altered by the interpretation of weak positive results. Using numerical analysis it was shown that most of the strains clustered according to source. Most reference cultures were more closely related to each other than they were to the regional strains. Some strains were phenotypically similar toVibrio splendidusbiovar I, which is arginine dihydrolase positive. Although there were differences, some strains were similar to the fish pathogenVibrio ordalii, which is negative for arginine dihydrolase. Both species are reported to grow at 4 °C. It was shown that most of the regionalVibrionaceaestrains studied were different from previously described species belonging to the familyVibrionaceae.Key words: numerical taxonomy,Vibrionaceae,Vibrio, marine bacteria, psychrotroph.

ISSN:0008-4166    

DOI:10.1139/m94-058

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A screening program was established to find actinomycetes that produce xylanases able to hydrolyze xylan chains in a hemicellulose liquor (a by-product of steam treatment of the lignocellulosic biomass) at moderately acidic pH (4.0) and high temperature (70 °C). The first step involved a selection for xylanolytic actinomycetes having optimal growth at 50–60 °C. In the second step, the crude enzymes produced by the selected actinomycetes were compared for their xylan hydrolysis rates at pH 5 and 60 °C versus pH 4 and 70 °C. The crude enzymes produced by strain FC7 retained 65% of their activity under the more stringent of the two conditions. FC7 was identified as a member of the genusActinomaduraby chemotaxonomic procedures. A gene bank of FC7 was constructed using the shuttle vector pFD666. The plasmids were introduced into a periplasmic-leakyEscherichia colihost to rapidly detect xylanolytic recombinants. Two classes of recombinants were isolated. The plasmids pJFl and pJF6 were introduced into a xylanase- and cellulase-negative mutant ofStreptomyces lividans, allowing overproduction and subsequent purification of two different xylanases, Xyl I and Xyl II. Both enzymes were classified in the low isoelectric point group of xylanases. In the presence of 100 μg/mL of bovine serum albumin, the half-life of Xyl I at pH 4 and 70 °C was 22 h.Key words: xylanase, thermophilic actinomycetes,Actinomadura, thermostability.

ISSN:0008-4166    

DOI:10.1139/m94-059

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Food pathogenic bacteria includingListeria monocytogenes(1A1 and ATCC 19111),Staphylococcus aureus(GD13 and ATCC 13565),Escherichia coli0157:H7 (ATCC 35150),Salmonella typhimurium,Yersinia enterocolitica,Vibrio parahaemolyticus, andCampylobacter jejuniwere exposed to various rates of ionizing radiation (0.78, 2.6, and 22 kGy/h) emitted by three different60Co irradiators.D10values (D10is the radiation dose required to eliminate 90% of a bacterial population (one logarithmic cycle reduction)) were calculated for the various strains and growth conditions tested. A covariance analysis of these results revealed that the dose rates studied had no significant influence on the radiosensitivity of these bacteria. At all dose rates, the bacteria were more radiosensitive when irradiated in a saline solution (0.85% NaCl) than in a chicken breast meat suspension. The growth phase of the bacterial population had a variable influence on its radioresistance. ForL.monocytogenes1A1,Staphylococcus aureusATCC 13565,E.coli0157:H7,Y.enterocolitica, andV.parahaemolyticus, radioresistance was not significantly different in the exponential and stationary phases. Populations ofL.monocytogenesATCC 19111 andStaphylococcus aureusGD13 were significantly more resistant in the stationary phase (D10 = 0.23 and 0.12 kGy, respectively) than in the exponential phase (D10 = 0.17 and 0.09 kGy, respectively). Among the pathogenic bacteria investigated in this study, the most radioresistant wasL.monocytogenes(D10 = 0.16–0.38 kGy, Gram-positive bacilli) and the most radiosensitive wasV.parahaemolyticus(D10 = 0.03–0.04 kGy, halophilic Gram-negative bacilli).Key words: ionization, food pathogenic bacteria, dose rate effect, radioresistance.

ISSN:0008-4166    

DOI:10.1139/m94-060

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Vibrio alginolyticus,Vibrio logei,Vibrio natriegens, andVibrio nerieswere grown in nutrient-limited continuous cultures at generation times (TD) of 5–135 h on complex media with cell yields of 0.8–12 × 106bacteria/mL. Average cell volume, as determined by image analysis of video fluorescence microscopy, decreased forV.logeiandV.neries, did not change forV.alginolyticus, and increased forV.natriegenswith increasingTD. The increase in cell volume observed forV.natriegenswas due to the development of filamentous cells. Batch cultures were grown on media with 10 times the nutrient concentration of continuous cultures. Tritiated thymidine incorporation was measured using phenol–chloroform extractions; leucine incorporation was measured in trichloroacetic acid precipitates. At concentrations of exogenous thymidine high enough to inhibit de novo synthesis of thymidine, the number of bacteria produced per mole of thymidine incorporated did not vary with changing generation time, or between batch and continuous cultures examined in this study. However, the number of bacteria produced per mole of leucine incorporated decreased per unit production with increasingTDfor all four vibrios. A significant difference in the bacterial production conversion factor (bacteria produced per mole of label incorporated) for thymidine was found forV.neriesrelative to the three otherVibriospecies, but no significant differences were found between growth conditions within species. Corrections for biovolume differences between species and growth rates reduced variability in conversion factors, and also yielded a significantly different conversion factor forV.neries. Conversion factors for leucine incorporation spanned three orders of magnitude, from 1015to 1018bacteria/mol of leucine incorporated.Key words: leucine, thymidine, bacterial production, chemostats.

ISSN:0008-4166    

DOI:10.1139/m94-061

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The culturability ofPseudomonas putidacells after exposure to hydrogen peroxide and antibiotics was correlated with growth-dependent expression of catalase isozymes. Exponential phase wild-type cells, which contained catalase isozyme A, survived a 15-min treatment with less than 4 mM hydrogen peroxide, but were killed by higher concentrations. The culturability ofP.putidamutant JIM, which lacked any functional catalase in exponential phase, was reduced by more than 75% after a 15-min exposure to ≥ 0.25 mM hydrogen peroxide. Because submillimolar concentrations of hydrogen peroxide are physiologically relevant in the bacterial cell, our results demonstrate that catalase isozyme A has essential housekeeping functions for growing cultures ofP.putida. The accumulation of catalase isozymes B and C during growth into stationary phase coincided with a decrease in the sensitivity of wild-type and JIM cells ofP.putidato hydrogen peroxide. Late stationary phase wild-type cells survived a 15-min exposure to even 50 mM hydrogen peroxide and mutant J1M cells survived exposure to 20 mM but not 50 mM hydrogen peroxide. The antibiotics tetracycline and kanamycin, which inhibit protein synthesis, were used to study the role of catalase induction in resistance to hydrogen peroxide. More than 40 and 80% of exponential phase cells ofP.putidawild-type and J1M strains, respectively, were rendered nonculturable after a 20-min exposure to 45 μM tetracycline. Surprisingly, stationary phase cells of bothP.putidastrains were culturable after a 20-min exposure to tetracycline but remained sensitive to kanamycin. Exposure to tetracycline of stationary phase cells did not reduce the resistance of these cells to hydrogen peroxide. Tetracycline but not kanamycin increased the activity of catalase in lysates prepared fromP.putidawild-type and mutant cells in early stationary growth phase. At this growth phase, only catalase isozyme B is operational in both strains, which suggests that tetracycline affects the activity of this enzyme.Key words:Pseudomonas putida, antibiotics, catalase, culturability, growth phase.

ISSN:0008-4166    

DOI:10.1139/m94-062

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The effect of a chromated-copper-arsenate wood preservative on the degradation of pentachlorophenol byFlavobacteriumsp. strain ATCC 53874 was examined in liquid culture. Both a commercially available and a laboratory-prepared formulation were tested. Each increased the lag time required for measurable pentachlorophenol degradation and the time required for complete degradation to nondetectable levels. This response was noted at all pentachlorophenol concentrations examined (10, 25, 50, 75, and 100 μg∙mL−1). The commercial formulation of chromated-copper-arsenate had the more significant impact on pentachlorophenol degradation. Inhibitory effects were evident at chromated-copper-arsenate component metal concentrations 0.1–0.5 mg∙L−1. These levels are thousands of times below those used commercially.Key words: pentachlorophenol, biodegradation, chromated-copper-arsenate, toxic

ISSN:0008-4166    

DOI:10.1139/m94-063

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Production of the amino acid 2-aminobutyrate was studied in four strains ofMegasphaera elsdeniigrown on a lactate-based growth medium containing Bacto-casamino acids and yeast extract. Supplementation with threonine increased the production of 2-aminobutyrate in three of the four strains, but no substantial increase in production was noted with serine, methionine, or aspartate, all of which are potential sources for the precursor of 2-aminobutyrate, 2-oxobutyrate.L-Cycloserine, an inhibitor of alanine transaminases, decreased both alanine and 2-aminobutyrate production, suggesting that 2-aminobutyrate synthesis may share the same metabolic pathway as alanine synthesis or that 2-oxobutyrate can act as a substrate for alanine transaminases. Decreases in the production of 2-aminobutyrate were associated with a reduction in the catabolism of branched-chain amino acids in two of the four strains.Key words:Megasphaera, amino acid, degradation, 2-aminobutyrate, rumen.

ISSN:0008-4166    

DOI:10.1139/m94-064

出版商:NRC Research Press    

年代:1994

数据来源: NRC