摘要:

InEscherichia coli, dihydrofolate reductase is required for both the de novo synthesis of tetrahydrofolate and the recycling of dihydrofolate produced during the synthesis of thymidylate. The coding region of the dihydrofolate reductase gene,folA, was replaced with a kanamycin resistance determinant. Unlike earlier deletions, this mutation did not disrupt flanking genes. When the mutation was transferred into a wild-type strain and a thymidine- (thy) requiring strain, the resulting strains were viable but slow growing on rich medium. Both synthesized less folate than their parents, as judged by the incorporation of radioactivepara-aminobenzoic acid. The derivative of the wild-type strain did not grow on any defined minimal media tested. In contrast, the derivative of the thy-requiring strain grew slowly on minimal medium with thy but exhibited auxotrophies on some combinations of supplements. These results suggest that when folates are limited, they can be distributed appropriately to folate-dependent biosynthetic reactions only under some conditions.Key words: dihydrofolate reductase,Escherichia coli, biosynthesis, folates, one-carbon metabolism.

ISSN:0008-4166    

DOI:10.1139/w98-229

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

APseudomonassp. (S1), isolated from soil by an enrichment technique was tested for its potential to degrade different cyanide compounds. Further, biodegradation/biotransformation of binary mixtures of the cyanide compounds by the culture was also studied. The results indicated that the culture could grow on the following nitriles by using them as carbon and nitrogen sources: acetonitrile, butyronitrile, acrylonitrile, adiponitrile, benzonitrile, glutaronitrile, phenylacetonitrile, and succinonitrile. Studies on the biodegradation of these cyanide compounds in binary mixtures showed that the presence of acrylonitrile or KCN delayed the degradation of acetonitrile in a mixture, while none of the other cyanide compounds affected the degradation of one another. The transformation products of the nitriles were their corresponding acids, and similarly, KCN was also directly transformed to formic acid. Studies on the transformation of these cyanide compounds showed that the rate of transformation of nitriles to their corresponding carboxylic acids was acrylonitrile > acetonitrile > adiponitrile > benzonitrile > KCN. This culture has the unique characteristic of transforming representatives of saturated aliphatic, aliphatic olefinic, aromatic, and aralkyl nitriles, as well as alkali cyanide, to their corresponding carboxylic acids.Key words:Pseudomonassp.(S1), biodegradation, biotransformation, nitriles, cyanide.

ISSN:0008-4166    

DOI:10.1139/w99-014

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Nine bacterial strains that grew on morpholine and pyrrolidine as sole carbon, nitrogen, and energy sources were isolated from three different environments with no known morpholine contamination. One of these strains could also degrade piperidine. These bacteria were identified asMycobacteriumstrains. A phylogenetic analysis based on the partial 16S rDNA sequences indicated that the isolated strains clustered within the fast growing group of mycobacteria. When the above-mentioned cyclic amines were used as growth substrates, the synthesis of a soluble cytochrome P450 was induced in all these bacteria. Other laboratory strains,Mycobacterium fortuitumandMycobacterium smegmatismc2155, were tested for their abilities to degrade morpholine. Neither of them degraded morpholine but could use pyrrolidine and piperidine. The growth ofM. fortuitumandM. smegmatismc2155 on these compounds involved a soluble cytochrome P450, suggesting that mycobacterial strains are naturally able to use pyrrolidine and have developed a similar enzymatic pathway to metabolize this amine.Key words: mycobacteria, morpholine, piperidine, pyrrolidine, cytochrome P450.

ISSN:0008-4166    

DOI:10.1139/w99-002

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The keratinase production by the thermophilic actinomycete strainThermoactinomyces candiduswas induced by sheep wool as the sole source of carbon and nitrogen in the cultivation medium. For complete digestion of wool by the above strain, both keratinolytic serine proteinase and cellular reduction of disulfide bonds were involved. Evidence was presented that substrate induction was a major regulatory mechanism and the keratinase biosynthesis was not completely repressed by addition of other carbon (glucose) and nitrogen (NH4Cl) sources. The enzyme was purified 62-fold by diethylaminoethyl - anion exchange and Sephadex G-75 gel permeation chromatographies. Sodium dodecyl sulfate - polyacrylamide gel electrophoresis indicated that the purified keratinase is a monomeric enzyme with a molecular mass of 30 kDa. The pH and temperature optima were determined to be 8.6 and 70°C, respectively. The purified thermophilic keratinase catalyses the hydrolysis of a broad range of substrates and displays higher proteolytic activity against native keratins than other proteinases. Ca2+was found to have a stabilizing effect on the enzyme activity at elevated temperatures.Key words: wool degradation, keratinolyic actinomycetes, keratinase,Thermoactinomyces candidus

ISSN:0008-4166    

DOI:10.1139/w98-230

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The conversion factor between acetylene reduction and15N incorporation in free-living cyanobacteria was determined in different high arctic habitats in the area of Ny-Ålesund (78.5°N, 11.6°E), Spitsbergen, in the summer of 1994. The experiments were carried out under constant conditions, 19°C and 200 µE·m-2·s-1. The nitrogen-fixation activities, measured as15N-incorporation, were in the range 4.01-6.54 mg N2fixed·gdw-1·day-1(dw, dry weight) in sheets ofNostoc communeand 778-1206 mg N2fixed·m-2·day-1in the cyanobacterial crusts. The acetylene reduction activities were in the range 0.72-1.91 mg ethylene produced·gdw-1·day-1ofN. communeand 12.8-63.7 mg ethylene produced·m-2·day-1in the cyanobacterial crusts. The conversion factor ofN. communeranged from 0.11 to 0.48 for ethylene produced to nitrogen fixed, whereas the cyanobacterial crusts covering the soil surface gave conversion factors in the range 0.022-0.073 for ethylene produced to nitrogen fixed. AnAnabaenasp., isolated from one of the habitats investigated, gave conversion factors near the theoretical factor of 4, when determined at 14.0 and 17.3°C. It was concluded that the acetylene reduction activity of free-living cyanobacteria in high arctic habitats results in underestimates of the real nitrogen-fixation activity in these environments.Key words: nitrogen fixation, acetylene reduction, conversion factor, cyanobacteria,Nostoc commune, high arctic

ISSN:0008-4166    

DOI:10.1139/w98-219

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Swine proliferative enteropathy is an enteric disease caused byLawsonia intracellulariswhich affects animals between 6 and 20 weeks of age, causing diarrhea, anorexia, and poor growth. The presence ofL. intracellulariswas evaluated in the faecal samples of 636 swine from 75 randomly chosen herds in the main swine-producing regions of Brazil. The pathogen was detected by the polymerase chain reaction method (PCR) usingL. intracellularisspecific primers. A 319-bp DNA fragment specific forL. intracellulariswas produced on amplification of DNA from the faeces of pigs with proliferative enteropathy. Equal amounts of DNA extracted from the faeces of animals from the same herd were pooled together and, onceL. intracellulariswas detected, the faecal material of each animal was analyzed separately. The incidence ofL. intracellulariswas 33.4% in the state of Santa Catarina, 29.4% in Paraná, 26.3% in Minas Gerais, 16.7% in Mato Grosso, and 7.1% in São Paulo. The presence of the pathogenic agent was detected in samples from 15 farms, representing a total incidence of 20%. Although 46 animals (7.2%) were shown to be infected, 11% did not present any symptoms of swine proliferative enteropathy. The use of PCR allowed the detection ofL. intracellularisin swine farms and the evaluation of the incidence of proliferative enteropathy in different regions of Brazil.Key words: proliferative enteropathy, diagnosis,Lawsonia intracellularis, PCR, incidenc

ISSN:0008-4166    

DOI:10.1139/w98-234

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A methanogenic consortium was used to degrade phenol andortho- (o-) cresol from a specific effluent of a petrochemical refinery. This effluent did not meet the local environmental regulations for phenolic compounds (178 mg/L), oils and greases (61 mg/L), ammoniacal nitrogen (75 mg/L) or sulfides (3.2 mg/L). The consortium, which degrades phenol via its carboxylation to benzoic acid, was progressively adapted to the effluent. Despite the very high effluent toxicity (EC50of 2% with Microtox), the adapted consortium degraded 97% of 156 mg/L phenol in the supplemented effluent after 13 days in batch cultures (serum bottle). The addition of proteose peptone to the effluent is essential for phenol degradation.o-cresol was also transformed but notmeta- orpara-cresols. A continuous flow fixed-film anaerobic bioreactor was developed with the consortium. Treating the effluent with the bioreactor reduced phenol and phenolic compounds concentrations by 97 and 83%, respectively, for a hydraulic residence time of 6 h. This treatment also reduced by about half the effluent toxicity. Oils and greases and ammoniacal nitrogen were not affected. Similar microbiological forms were observed in serum bottles and in the bioreactors with or without the petrochemical effluent. These results indicate that this methanogenic consortium can treat efficiently the phenolic compounds in this specific petrochemical effluent.Key words: phenolic compounds, anaerobic consortium, petrochemical effluent, biodegradation, methanogenic conditions.

ISSN:0008-4166    

DOI:10.1139/w98-228

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Scanning electron microscopy was used to detect ultrastructural protuberances on the cellulolytic anaerobeClostridium cellulovorans. Numerous ultrastructural protuberances were observed on cellulose-grown cells, but few were detected on glucose-, fructose-, cellobiose-, or carboxymethylcellulose (CMC)-grown cells. Formation of these protuberances was detected within 2 h of incubation in cellulose medium, but 4 h incubation was required before numerous structures were observed on the cells. When a soluble carbohydrate or CMC was mixed with cellulose-grown cells, the ultrastructural protuberances could no longer be detected. In fact, no protuberances were observed within 5 min following the addition of glucose, cellobiose, or methylglucose to cellulose-grown cells. The presence of these protuberances corresponded with the binding of theBandeiraea simplicifoliaBSI-B4isolectin to the cell. Cellulose-grown cells had a greater level of observable lectin binding than cellobiose-grown cells, and lectin binding was not detected on glucose- or fructose-grown cells. In addition, lectin binding ability was lost by cellulose-grown cells following the addition of glucose, fructose, or methylglucose to the cellulose medium. A cellulose-affinity protein fraction expressing cellulase activity was also detected in cell extracts of cellobiose- or cellulose-grown cultures. However, this protein fraction was not detected in extracts of glucose-grown cultures, and was rapidly lost (within 5 min) following the addition of glucose to cellulose-grown cultures. The ability ofC. cellulovoransto adhere to cellulose was also affected by the energy substrate, but not in the same manner as the protuberance formation or the cellulase-containing protein fraction. Rather, cellobiose-, cellulose-, and CMC-grown cultures adhered to cellulose, but this adherence was not affected by addition of glucose to the medium. This is the first report that soluble carbohydrates caused the rapid loss of some cellulose-inducible systems ofC. cellulovorans.Key words: cellulolytic bacteria, bacterial ultrastructure, polycellulosome, scanning electron microscope, lectin binding, cellulosome.

ISSN:0008-4166    

DOI:10.1139/w99-004

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Since menstrual toxic shock syndrome (MTSS) is associated with a predominant clone ofStaphylococcus aureuswhich produces both toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin A (SEA), we sought to clarify the role of TSST-1 in a tampon-associated vaginal infection model in New Zealand White (NZW) rabbits, using isogenictst+/sea+S. aureusmutants in whichtstwas inactivated by allelic replacement. Rabbits infected with thetst-/sea+strain became ill within 3 days, with fever, weight loss, conjunctival hyperemia, and lethargy. Mortality was significantly higher with thetst+/sea+strain compared to itstst-/sea+isogenic derivative (4/13 vs. 0/14;p< 0.05, Fisher's exact test, 2-tailed). Mean fever index was higher (p< 0.005; t test, 2-tailed) and weight loss more sustained among survivors in thetst+/sea+group. Furthermore, culture filtrates from thetst+/sea+strain induced a significantly greater response in mitogenesis and TNFalpha secretion from rabbit splenocytes in vitro compared to thetst-/sea+isogenic derivative. Thus, regardless of the role of SEA, TSST-1 significantly contributed to both morbidity and mortality in this tampon-associated vaginal infection model in NZW rabbits. This is the first demonstration of the potential role of TSST-1 and SEA in the pathogenesis of MTSS with a MTSS-associated clinicalS. aureusstrain in a relevant animal model.Key words: toxic-shock syndrome toxin-1, superantigens, rabbit model.

ISSN:0008-4166    

DOI:10.1139/w99-015

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The extent of reduction in selected microorganisms was tested during both aerobic wastewater treatment and anaerobic digestion of sludge at the wastewater treatment plant in Ottawa to compare the removal of two encysted pathogenic protozoa with that of microbial indicators. Samples collected included the raw wastewater, the primary effluent, the treated wastewater, the mixed sludge, the decanted liquor, and the cake. All of the raw sewage samples were positive forCryptosporidiumoocysts andGiardiacysts, as well as for the other microorganisms tested. During aerobic wastewater treatment (excluding the anaerobic sludge digestion),CryptosporidiumandGiardiawere reduced by 2.96 log10and 1.40 log10, respectively.Clostridium perfringensspores,Clostridium perfringenstotal counts, somatic coliphages, and heterotrophic bacteria were reduced by approximately 0.89 log10, 0.96 log10, 1.58 log10, and 2.02 log10, respectively. All of the other microorganisms were reduced by at least 3.53 log10. Sludge samples from the plant were found to contain variable densities of microorganisms. Variability in microbial concentrations was sometimes great between samples, stressing the importance of collecting a large number of samples over a long period of time. In all cases, the bacterial concentrations in the cake (dewatered biosolids) samples were high even if reductions in numbers were observed with some bacteria. During anaerobic sludge digestion, no statistically significant reduction was observed forClostridium perfringens,Enterococcussp.,Cryptosporidiumoocysts, andGiardiacysts. A 1-2 log10reduction was observed with fecal coliforms and heterotrophic bacteria. However, the method utilized to detect the protozoan parasites does not differentiate between viable and nonviable organisms. On the other hand, total coliforms and somatic coliphages were reduced by 0.35 log10and 0.09 log10, respectively. These results demonstrate the relative persistence of the protozoa in sewage sludge during wastewater treatment.Key words:Cryptosporidium,Giardia, indicators, wastewater, sludge.

ISSN:0008-4166    

DOI:10.1139/w99-001

出版商:NRC Research Press    

年代:1999

数据来源: NRC