摘要:

The relationship of polyketide melanogenesis molecular biology to that of nonmelanin-producing pathways in a wide range of fungi and other organisms is discussed. Analytical methods and fundamental properties of melanins are discussed and fungal melanin properties are compared with those of animal and bacterial melanins. The enzymatic degradation of melanins by lignin peroxidases is described.Key words: fungal melanin, polyketide melanin, DHN melanin, melanin degradation, melanin properties, melanin analysis.

ISSN:0008-4166    

DOI:10.1139/w98-119

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Mitotically unstableAspergillus nidulansargB+transformants obtained by the biolistic process were studied in the present work. Hybridization signals from undigested DNA and pulsed-field chromosomal bands of the transformants suggested the introduced plasmid occurred as free concatenated molecules. Fifteen vigorous growth sectors released from the transformants were analysed in order to understand the mechanisms involved in their formation. All sectors showed the integration of exogenous genes into the fungal genome by homologous or heterologous recombinant events.Key words:Aspergillus nidulans, biolistic process, mitotic instability, fungal transformation.

ISSN:0008-4166    

DOI:10.1139/w98-213

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Tetrachloroethylene (PCE) is a toxic compound essentially used as a degreasing and dry-cleaning solvent. A methanogenic and sulfate-reducing consortium that dechlorinates and mineralizes high concentrations of PCE was derived from anaerobically digested sludge obtained from a waste water treatment plant (Bourg-en-Bresse, France). A methanogenic bacterium, strain FR, was isolated from this acclimated consortium. On the basis of morphological and physiological characteristics, strain FR was classified in the genus ofMethanosarcina. Phylogeny analysis with the 16S rRNA gene sequence revealed that strain FR is highly related toMethanosarcina mazeiandMethanosarcina frisia(99.6 and 99.5% identity, respectively). High concentrations (50-87 &mgr;M) of PCE were completely dechlorinated by strain FR cultures at the rate of 76 nM·mg protein-1·day-1. PCE dechlorination produced a nonidentified compound. The tracer experiments with [13C]PCE revealed that the product was nonchlorinated. Dechlorination of PCE to trichloroethylene was still active in the presence of boiled cell extract of the strain FR. However, no further dechlorination was observed. This result suggests that a cofactor rather than an enzymatic system is responsible for the first dechlorination of PCE. Dechlorination-active fractions purified from cell extracts on a XAD-4 column revealed the presence of F420, F430, and cobamides cofactors. This is the first report of the isolation of a methanogenic bacterium with the ability to dechlorinate high concentrations of PCE to a nonchlorinated product.Key words: dechlorination,Methanosarcina, tetrachloroethylene.

ISSN:0008-4166    

DOI:10.1139/w98-126

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Previously reported hybridization data, obtained with the initial renaturation method (De Ley et al. 1970), were compared with data obtained with a microplate DNA - DNA hybridization method (Ezaki et al. 1989). The comparison was done for more than 82 hybridizations, within 4 sets ofBacillus/Virgibacillus,Myroides,Vibrio, andXanthomonas/Stenotrophomonasstrains, comprising DNA-base compositions ranging from 34 to 65%. Under the experimental conditions used, both methods were in very good correlation. With the microplate method, the variation between reciprocal hybridizations and repeated experiments was around 7%, while for the initial renaturation method, a 5% variation was calculated. It is concluded that the microplate method can be used as a reliable taxonomic tool.Key words: DNA, DNA hybridization, microplate method, initial renaturation method.

ISSN:0008-4166    

DOI:10.1139/w98-118

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Cryptosporidium parvumoocysts were aged in waters from both the St. Lawrence River and the Ottawa River. In situ survival experiments were carried out by incubating the oocysts in either dialysis cassettes or microtubes floated into an overflow tank. A significant portion of the oocysts survived in the test waters for several weeks. Oocyst survival in the St. Lawrence River was better in membrane-filtered (0.2-µm-pore diameter) water than in unfiltered water, suggesting that biological antagonism may play a role in the environmental fate of the parasite. Oocysts aged in river waters under in situ conditions and control oocysts kept refrigerated in synthetic water (100 ppm as CaCO3; pH 7.0) were subjected to the same disinfection protocol. Aged oocysts were at least as resistant as, if not more resistant than, the control oocysts to disinfection. This indicates that the oocysts surviving in the water environment may be just as difficult to inactivate by potable water disinfection as freshly shed oocysts. Therefore, water treatment should not be based on the assumption that environmental oocysts may be more easily inactivated than freshly shed oocysts. First-order kinetics die-off rates varied from one river to another (from 0.013 to 0.039 log10·day-1) and from one experiment to another with water from the same river collected at different times. Calculation of the die-off rates based on either in vitro excystation or in vitro excystation in combination with total counts (overall die-off rates) showed that the assessment of oocyst viability by microscopic methods must account for the total oocyst loss observed during long-term inactivation assays of river waters.Key words:Cryptosporidium, survival, disinfection, biological antagonism

ISSN:0008-4166    

DOI:10.1139/w98-113

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Monoclonal antibodies were generated against components on the surface of zoospores and cysts of the Oomycete,Phytophthora nicotianae, with the aim of obtaining antibodies diagnostic for this species of plant pathogen. A dipstick version of an enzyme-linked immunosorbent assay was used to screen hybridoma cell lines produced by following a coimmunization protocol in which a mouse was immunized withPhytophthoranicotianaecysts mixed with murine antisera raised against cysts ofPhytophthora cinnamomiandPhytophthora cryptogea. Of the nine hybridoma cells lines which remained positive, five produced antibodies that reacted with species-specific epitopes on the surface of the spores. Immunofluorescence, immunogold, and immunoblot labelling showed that three of the five species-specific antibodies reacted with a polypeptide of relative molecular mass greater than 205 kDa which was distributed over the entire zoospore surface, including that of the two flagella. These antibodies also labelled the surface of cysts to varying degrees. The other two species-specific antibodies bound to the shaft of tubular mastigonemes that form two rows on the anterior flagellum. In immunoblots, one of these antibodies recognised a 40-kDa glycoprotein. Antibodies produced by the other four hybridoma cell lines reacted with allPhytophthoraandPythiumspecies tested. The results (i) showed that the coimmunization technique effectively produced antibodies directed towards components specific forPhytophthora nicotianaein the presence of antigens common to manyPhytophthoraspecies, and (ii) revealed for the first time the biochemical nature of molecular constituents of flagellar mastigonemes in the Oomycetes.Key words: cell surface, flagella, immunodiagnostics, mastigonemes, monoclonal antibodies.

ISSN:0008-4166    

DOI:10.1139/w98-120

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

During anaerobic fermentation,Saccharomyces cerevisiaereleases large amounts of medium-chain fatty acids (MCFAs) and related ethyl esters which are very important for aromatic quality of fermented beverages. The physiological function of ester synthesis is not yet understood. As MCFAs are toxic, their conversion to esters has been proposed to be a detoxification mechanism. Esterases possess ester synthesizing ability. Throughout an anaerobic fermentation of a lipid-free synthetic medium carried out with aS. cerevisiaestrain selected for wine making, we have monitored MCFA and ethyl ester production and, at the same time, measured growth and esterasic activity of intact cells. Because no correlation was found between the concentration of each fatty acid and its ethyl ester, there is no evidence that ester synthesis reduces the toxicity of MCFAs. Esterasic activity did not show any correlation with ester synthesis, but it was related to the release of MCFAs. A model is proposed in which ester synthesis is a consequence of the arrest of lipid biosynthesis resulting from a lack of oxygen. Under these conditions, an excess of acyl coenzyme A is produced, and acyl esters are formed as secondary products of reactions aimed at recovering free coenzyme A.Key words: yeast, esterase, medium-chain fatty acids, toxicity, ethyl esters.

ISSN:0008-4166    

DOI:10.1139/w98-124

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Unlike most other indigenous bacteria, segmented filamentous bacteria (SFB) are potent activators of the mucosal immune system. SFB are strongly anchored to the epithelial cells of the small intestine where they have a preference for mucosal lymphoid epithelium. Since SFB are only present in high numbers shortly after weaning, it was investigated whether an SFB-induced immune reaction results in the removal of these bacteria from the small intestine. A correlation was found between age and colonization levels in the small intestines of SFB monoassociated Swiss mice. Five-week-old athymic BALB/c (nu/nu) mice showed lower colonization levels than their heterozygous littermates, but the opposite was found at the age of 12 weeks. However, SFB inoculation of germfree Swiss mice resulted in higher colonization levels in 5-week-old mice when compared with 4-month-old mice. We conclude that SFB colonization levels in the small intestine are likely influenced by the activity of the mucosal immune system. However, an additional age-dependent factor that modulates SFB colonization levels cannot be excluded.Key words: segmented filamentous bacteria, small intestine, gut-associated lymphoid tissue.

ISSN:0008-4166    

DOI:10.1139/w98-122

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Computer-assisted restriction endonuclease analysis of plasmid DNA in field strains ofSalmonella entericaserovar Enteritidis (S.enteritidis) is described. The procedure consists of plasmid DNA purification, its digestion with restriction endonucleaseTaqI, electrophoresis, charge-coupled device camera scanning of the gels, and an analysis of the restriction patterns with the software Gel Manager. The system allowed us to analyse, in detail, results of plasmid profiling in more than 600 field strains ofS.enteritidis. In addition to plasmid-free and virulence plasmid only containing strains, 15 additional plasmid types were detected. All the images and detailed protocols are available at the Web site http://www.clark.cz/vri/salmon.htm.Key words: computer analysis, plasmid type,Salmonella, DNA fingerprinting, epidemiology.

ISSN:0008-4166    

DOI:10.1139/w98-112

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

pGR71, a composite of plasmids pUB110 and pBR322, replicates inEscherichia coliand inBacillus subtilis. It carries the chloramphenicol resistance gene (cat) from Tn9, which is not transcribed in either host by lack of a promoter. Thecatgene is preceded by a Shine-Dalgarno sequence functional inE.colibut not inB.subtilis. Deleted pGR71 plasmids were obtained inB.subtiliswhen cloning foreign viral DNA upstream of thiscatsequence, as well as by BAL31 exonuclease deletions extending upstream from thecatinto the pUB110 moiety. These mutant plasmids expressed chloramphenicol acetyltransferase (CAT), conferring onB.subtilisresistance to high chloramphenicol concentrations. CAT expression peaked at the early postexponential phase ofB.subtilisgrowth. The transcription initiation site ofcat, determined by primer extension, was located downstream of a putative promoter sequence within the pUB110 moiety. N-terminal amino acid sequencing showed that native CAT was produced by these mutant plasmids. Thecatribosome-binding site, functional inE.coli, was repositioned within the pUB110 moiety and had consequently an extended homology withB.subtilis16S rRNA, explaining the production of native enzyme.Key words: chloramphenicol acetyltransferase,Bacillus subtilis, postexponential gene expression, plasmid pUB110, ribosome-binding site, transcriptional promoter.

ISSN:0008-4166    

DOI:10.1139/w98-121

出版商:NRC Research Press    

年代:1998

数据来源: NRC