ISSN:0008-4166    

DOI:10.1139/cjmcontents00

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The localization and expression of the hydrogenase in free-livingFrankiaKB5 was investigated immunologically and by monitoring activity, focusing on its relationships with nitrogenase and H2. Immunological studies revealed that the large subunit of the hydrogenase inFrankiaKB5 was modified post-translationally, and transferred into the membrane after processing. The large subunit was constitutively expressed and no correlation was found between hydrogenase activity and synthesis. Although H2was not needed for induction of hydrogenase synthesis, exogenously added H2triggered hydrogen uptake in medium containing nitrogen, i.e., in the hyphae. A correlation between nitrogenase activity and hydrogen uptake was found in cultures grown in media without nitrogen, but interestingly the two enzymes showed no co-regulation.Key words: hydrogenase, expression, nitrogenase,FrankiaKB5.

ISSN:0008-4166    

DOI:10.1139/w00-100

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Cytosolic glycerol kinase (Gut1p) and mitochondrial glycerol-3-phosphate dehydrogenase (Gut2p) constitute the glycerol utilization pathway inSaccharomyces cerevisiae. Transcriptional analysis of theGUT2gene showed that it was repressed by glucose and derepressed on the non-fermentable carbon sources, glycerol, lactate and ethanol. Derepression ofGUT2requires the protein kinase Snf1p as well as the heteromeric protein complex, Hap2/3/4/5, and its putative DNA-binding site (UASHAP) located in the promoter region. Furthermore, glucose repression ofGUT2requires the negative regulator, Opi1p.Key words:GUT2, mitochondrial glycerol-3-phosphate dehydrogenase, transcriptional regulation,Saccharomyces cerevisiae.

ISSN:0008-4166    

DOI:10.1139/w00-105

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Escherichia coliO115:F165 strains are associated with septicaemia in young pigs and synthesize fimbriae involved in virulence, designated as F1651. F1651fimbriae belong to the P fimbrial family and are encoded by thefoogene cluster. Thefooregulatory region of strain 5131 possesses characteristics similar to that of members of the P regulatory family, includingpapIandpapBhomologues, and two GATC sites separated by 102 bp, targets of differential Dam methylation. In wild-type strains, the synthesis of F1651is repressed by leucine and the fimbriae undergo phase variation. Immunofluorescence staining showed that phase variation of F1651results in a majority of cells (98%) in the ON phase, in contrast with phase variation of other members of this regulatory family, for which the majority of the cells are in the OFF state. Using a translational fusion in strain 5131 betweenphoAandfooA, encoding for the major structural subunit of F1651, it was shown that leucine inhibits the OFF to ON switch and modulates the basal transcription of thefoooperon.Key words:Escherichia coli, fimbriae, phase variation, regulation, septicaemia.

ISSN:0008-4166    

DOI:10.1139/w00-109

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A dairy product processing plant was studied for 2.5 years to examine contamination withStaphylococcus aureusand try to correlate the source of contamination. Cultures were submitted to an antibiotic susceptibility test (AST) and characterised by Pulsed-field Gel Electrophoresis (PFGE) analysis. Results showed that 35.2% (19/51) of food handlers were asymptomatic carriers ofS. aureus, and that 90.4% (19/21) of raw milk sampled was contaminated.Staphylococcus aureuswas isolated from only 10 samples among more than 3200 investigated dairy products. NoS. aureuscontamination was found on machinery. The AST analysis demonstrated sensitivity of testedS. aureusto oxacillin, cephalothin, vancomycin, gentamicin, and sulfamethoxazole/trimethoprim. AST analysis generated eight different phenotypic profiles, but did not allow us to identify the source of contamination in seven of ten final products. PFGE analysis proved to be a sensitive method as it generated 42 different DNA banding profiles among the 48S. aureusinvestigated, demonstrating a lack of predominance of endemic strains in the plant, contrary to suggestions raised by antibiotic resistance typing. Based on PFGE genotyping,S. aureusstrains isolated from four contaminated final products were similar to fourS. aureusisolated from raw milk. Five final products containedS. aureusdifferent from all other strains collected, and one showed similarity to a strain isolated from a food handler. These results suggest contamination by raw milk as the main source of contamination of the final dairy products.Key words:Staphylococcus aureus, dairy products, antibiotic susceptibility, PFGE.

ISSN:0008-4166    

DOI:10.1139/w00-111

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

PCR/RFLP of the NTS2 (IGS2) of rDNA was applied to differentiate two closely related yeast species,Kluyveromyces lactisvar.lactis(referred to asK. lactis) andK. marxianus. Using specific primers, the NTS2 region was amplified from DNA of bothK. lactisandK. marxianustype and collection strains.AluI restriction of amplified fragments generated patterns characteristic for each species. The NTS2 region fromK. lactisvar.drosophilarumand related speciesK. aestuarii,K. africanus,K. dobzhanskii,andK. wickerhamiicould also be amplified with the same primers, butAluI patterns generated were clearly different. PCR/RFLP of the NTS2 appears thus to be a convenient method for rapid identification ofK. lactisandK. marxianus, frequently found in dairy products. This test was validated therefore onK. lactisandK. marxianusfrom natural habitats. We showed that all yeast strains collected from whey samples and scoring blue on X-gal glucose plates were eitherK. lactisorK. marxianus. For application purposes, we propose here an approach for quickly screening forK. lactis/marxianusandSaccharomycescerevisiaein dairy products using X-gal coloured and lysine growth media.Key words: yeast,Kluyveromyces, ribosomal DNA, karyotype, taxonomy.

ISSN:0008-4166    

DOI:10.1139/w00-107

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

As components of starter cultures for Bulgarian yogurt,Streptococcus salivariussubsp.thermophilusandLactobacillus delbrueckiisubsp.bulgaricusrevealed extensive exopolysaccharide (EPS) production activity when cultivated in whole cow's milk. The polymer-forming activity of thermophilic streptococci was lower (230-270 mg EPS/L) than that of the lactobacilli (400-540 mg EPS/L). Mixed cultures stimulated EPS production in yogurt manufacture, and a maximum concentration of 720-860 mg EPS/L was recorded after full coagulation of milk. The monomer structure of the exopolysaccharides formed by the yogurt starter cultures principally consists of galactose and glucose (1:1), with small amounts of xylose, arabinose, and/or mannose.Key words:Streptococcus thermophilus, Lactobacillus bulgaricus,starter cultures, yogurt, exopolysaccharides.

ISSN:0008-4166    

DOI:10.1139/w00-103

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

In order to isolate and characterize new strawberry-associated bacteria antagonistic to the soil-borne pathogenic fungusVerticillium dahliaeKleb., rhizobacterial populations from two different strawberry species, Greenish Strawberry (Fragaria viridis) and Garden Strawberry (F. × ananassa) obtained after plating onto King's B and glycerol-arginine agar, were screened for in vitro antagonism towardV. dahliae. The proportion of isolates with antifungal activity determined in in vitro assay againstV. dahliaewas higher for the Garden Strawberry than for the Greenish Strawberry. From 300 isolates, 20 isolates with strong antifungal activity were selected characterized by physiological profiling and molecular fingerprinting methods. Diversity among the isolates was characterized with molecular fingerprints using amplified ribosomal DNA restriction analysis (ARDRA) and the more discriminating BOX-PCR fingerprint method. The physiological profiles were well correlated with molecular fingerprinting pattern analysis. Significant reduction of Verticillium wilt by bacterial dipping bath treatment was shown in the greenhouse and in fields naturally infested byV. dahliae. The relative increase of yield ranged from 117% (Streptomyces albidoflavusS1) to 344% (Pseudomonas fluorescensP10) in greenhouse trials, and 113% (Streptomyces albidoflavusS1) to 247% (Pseudomonas fluorescensP6) in field trials. Evaluation resulted in the selection of three effective biocontrol agents (Pseudomonas fluorescensP6, P10, andStreptomyces diastatochromogenesS9) antagonistic to the Verticillium wilt pathogen.Key words: biocontrol, molecular fingerprint, antifungal properties,Pseudomonas,Streptomyces

ISSN:0008-4166    

DOI:10.1139/w00-101

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Restriction fragment length polymorphisms (RFLP) were examined in three isoforms of a gene family encoding subtilisin-like proteases (Pr1A,Pr1B, andPr1C)in several isolates of the entomopathogenic fungusMetarhizium anisopliae. RFLP variation was not observed in any of thePr1genes from isolates within the same genetically related group. Between genetically related groups and between isolates from disparate geographical areas, the greatest variation in RFLP patterns was observed forPr1A. When variation does occur atPr1BandPr1C, it was generally observed at anEcoRI site.Metarhizium anisopliaevar.majusstrain 473 and aM. flavovirideisolate were most dissimilar in RFLP patterns at allPr1genes when compared to theM. anisopliaestrains. We suggest thatPr1genes represent a gene family of subtilisin-like proteases and that thePr1Agene encodes for the ancestral subtilisin-like protease which has subsequently duplicated and rearranged within the genome.Key words:Metarhizium anisopliae, protease, RFLP, entomopathogen.

ISSN:0008-4166    

DOI:10.1139/w00-112

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We describe the new yeast speciesWickerhamiella lipophila, the teleomorph ofCandida lipophila, a haploid heterothallic yeast previously isolated from insects associated with morning glories in Hawaii. Both mating types were recovered in the eastern region of Maui, and a single strain was found in the Waimea region of Kauai. We reexamined the mating compatibility of the several strains ofCandida lipophilapreviously collected on the island of Hawaii and found them to be fertile mating types that had been overlooked because of the unpredictability of mating and ascus formation. The type culture ofCandida lipophila[UWO(PS)91-681.3 = CBS 8458, h+] is transferred to the genusWickerhamiella, and strain UWO(PS)00-340.1 (CBS 8812, h-) is designated as isotype. Also found on Maui and Kauai were strains ofCandida drosophilaethat produced a strong extracellular protease. An update on the global distribution of members of theWickerhamiellaclade is given.Key words: yeasts,Wickerhamiella,Candida, flowers, insects, biogeography.

ISSN:0008-4166    

DOI:10.1139/w00-108

出版商:NRC Research Press    

年代:2000

数据来源: NRC