摘要:

Yeast predation was studied with respect to the range of its distribution among ascomycetous yeasts, the range of yeast species that can be affected, and nutritional aspects of the phenomenon. The yeasts identified as predators belong to theSaccharomycopsisclade as defined on the basis of rDNA sequence relatedness. The 11 recognized species in the clade, plus three undescribed but relatedCandidaspecies, were shown to be incapable of utilizing sulfate as sole source of sulfur, and all but two (Saccharomycopsis capsularisandSaccharomycopsis vini) were observed to penetrate and kill other yeasts under some conditions. Other unrelated sulfate transport-deficient yeasts (strains in the generaPichiaandCandidaand the two known species ofStarmera) are not predacious. The predacious species vary considerably as to the optimal environmental conditions that favour predation. Some are inhibited by the presence of rich nitrogenous nutrients, organic sulfur compounds, or higher concentrations of ammonium nitrogen, whereas other species may be stimulated under the same conditions. An attempt was made to correlate prey susceptibility to the excretion of substances that stimulate the growth of predators, but no correlation was detected between the two phenomena. The range of susceptible prey covers both ascomycetes and basidiomycetes, and includesSchizosaccharomyces pombe, which was previously thought to be immune. The achlorophyllous algaPrototheca zopfiiis not killed by predacious yeasts, but the initial steps of penetration have been observed in some cases. Predacious species attack other predacious species, and in some cases, young cultures may penetrate older cultures of the same strain.Key words: predacious yeasts, sulfate transport deficiency,Saccharomycopsis.

ISSN:0008-4166    

DOI:10.1139/w00-021

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Fatty-acid biosynthesis by a branched-chain alpha-keto acid dehydrogenase (bkd) mutant ofStreptomyces avermitiliswas analyzed. This mutant is unable to produce the appropriate precursors of branched-chain fatty acid (BCFA) biosynthesis, but unlike the comparableBacillus subtilismutant, was shown not to have an obligate growth requirement for these precursors. Thebkdmutant produced only straight-chain fatty acids (SCFAs) with membrane fluidity provided entirely by unsaturated fatty acids (UFAs), the levels of which increased dramatically compared to the wild-type strain. The levels of UFAs increased in both the wild-type andbkdmutant strains as the growth temperature was lowered from 37°C to 24°C, suggesting that a regulatory mechanism exists to alter the proportion of UFAs in response either to a loss of BCFA biosynthesis, or a decreased growth temperature. No evidence of a regulatory mechanism for BCFAs was observed, as the types of these fatty acids, which contribute significantly to membrane fluidity, did not alter when the wild-typeS. avermitiliswas grown at different temperatures. The principal UFA produced byS. avermitiliswas shown to be delta9-hexadecenoate, the same fatty acid produced byEscherichia coli. This observation, and the inability ofS. avermitilisto convert exogenous labeled palmitate to the corresponding UFA, was shown to be consistent with an anaerobic pathway for UFA biosynthesis. Incorporation studies with theS. avermitilis bkdmutant demonstrated that the fatty acid synthase has a remarkably broad substrate specificity and is able to process a wide range of exogenous branched chain carboxylic acids into unusual BCFAs.Key words:Streptomyces avermitilis, fatty acid biosynthesis, avermecti

ISSN:0008-4166    

DOI:10.1139/w00-028

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A quality model has been developed from parameters determining the interactions of physical, chemical, and biological factors during the preparation of mushroom compost for growingAgaricus bisporus. Our results show that a partial least square model based on the combination of pH, dry matter, ammonia, carbon, hydrogen, ash, Cu, Fe, and Na could explain nearly 90% of the variation in mushroom yield obtained from four compost comparative trials. The yields in the data base for generating the model ranged from 138 to 305 kg per tonne of compost. The validity of the yield model has been confirmed in a trial carried out in collaboration with experienced commercial growers. This has significant implications for compost producers, as production efficiencies can be maintained by targeting the important parameters.Key words:Agaricus bisporus,compost quality, partial least squares model, modelling, physiology.

ISSN:0008-4166    

DOI:10.1139/w00-012

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The rice sheath blight pathogen,Rhizoctonia solani,produces a toxin designated as RS-toxin, a carbohydrate compound containing mainly alpha-glucose and mannose. Different microflora were tested for RS-toxin inactivation. Isolates ofTrichoderma virideinactivated this toxin when it was provided as the sole food source, and these isolates reduced the severity of toxin-induced symptoms and electrolyte leakage from rice cells. The best-performing isolate, TvMNT7, produced two extracellular proteins of 110 and 17 kDa. The high molecular mass protein was shown to have alpha-glucosidase activity. The purified 110 kDa protein was able to reduce RS-toxin activity.Key words: rice sheath blight disease,Rhizoctonia solani, RS-toxin, toxin inactivation,Trichoderma viride.

ISSN:0008-4166    

DOI:10.1139/w00-018

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Candida guilliermondiiUFMG-Y65, isolated from a gold mine, was able to utilize different nitriles and the corresponding amides as sole source of nitrogen, at concentrations up to 2 M. Resting cells cultivated on YCB-acetonitrile medium showed nitrile hydrolyzing enzyme activities against acrylonitrile and benzonitrile. These enzymes were inducible and intracellular; the optimum pH was 7.0-8.0, and the optimum temperature 25°C-30°C. Liquid chromatographic analysis indicated thatC. guilliermondiiUFMG-Y65 metabolized 12 mM benzonitrile to 11 mM benzoic acid and 10 mM acrylonitrile to 7.9 mM acrylic acid. The results suggest thatC. guilliermondiiUFMG-Y65 may be useful for the bioproduction of amides and acids, and for the bioremediation of environments contaminated with nitriles.Key words:Candida guilliermondii, nitrile hydrolyzing enzyme, amidase, nitriles, amide

ISSN:0008-4166    

DOI:10.1139/w00-027

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The expression of a monoclonal antibody Fab fragment inEscherichia colistrain RB791/pComb3, induced with either lactose or isopropyl-beta-D-thiogalactoside (IPTG), was compared to determine if lactose might provide an inexpensive alternative to induction with IPTG. Induction of Fab expression imposed a metabolic load on the recombinant cells, resulting in lower final cell yields compared to the non-induced controls. An IPTG concentration of 0.05 mM was sufficient to achieve maximal expression of soluble Fab protein when inducing in the early-, mid-, or late-log phases of batch cultures grown using either glucose or glycerol as a carbon source. The largest overall yield of Fab fragments when using 0.05 mM IPTG was achieved by increasing the final yield of cells through glycerol feeding following induction in late-log phase. Lactose was as effective as IPTG for inducing Fab expression inE. coliRB791/pComb3. The greatest overall level of Fab expression was found when cells grown on glycerol were induced with 2 g/L lactose in late-log phase. Since the cost of 0.05 mM of IPTG is significantly greater than the cost of 2 g/L lactose, lactose provides an inexpensive alternative to IPTG for inducing the expression of Fab fragments, and possibly other recombinant proteins, from theE.colilacpromoter.

ISSN:0008-4166    

DOI:10.1139/w00-026

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Isolates ofEnterococcus faecalisobtained from a swine farrowing house outflow were examined for genetic elements similar to Tn916. Of the enterococci isolated, 71% were resistant to tetracycline. Among the tetracycline-resistant enterococci isolated from the outflow samples, approximately 34% were able to transfer the tetracycline resistance phenotype toBacillus thuringiensisin cross-genus matings. The frequencies of transfer for 10 random isolates were comparable to those for transfer of Tn916fromE. faecalistoB. thuringiensis. In addition, these elements were shown to mobilize plasmid pC194 betweenBacillusspecies, as did Tn916. Southern blot and polymerase chain reaction (PCR) analysis showed these elements share extensive structural homology with Tn916. The selected conjugal elements were capable of transfer to aBacillusrecipient in a soil environment. When the swine waste was introduced into the soil, the tetracycline resistant fecal enterococci levels rose from essentially undetectable levels to approximately 4 × 104and remained at this level for 4 weeks. After six months, including one winter, levels had decreased to 5 × 103.Key words:Enterococcus faecalis, Tn916, swine waste, genetic exchange,Bacillus thuringiensis, PC

ISSN:0008-4166    

DOI:10.1139/w00-029

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The use of lignocellulolyticStreptomycesspp. as biological agents, to enhance thatch degradation in turf and to slow its rate of accumulation while controlling fungal growth in the thatch layer, was studied. In flask scale studies, two lignocellulolyticStreptomyces violaceusniger(= hygroscopicus) strains (YCED9 and WYE53) decomposed thatch (>30% dry weight) over a 12-week incubation period. Biodegradation was accompanied by production of extracellular cellulases, xylanases, and peroxidases. The accumulation of the polymeric, water-soluble lignin degradation intermediate acid, precipitable polymeric lignin (APPL), was also observed. Residual thatch from 12-week-old cultures had an increased lignin-to-carbohydrate ratio, an indication that although lignin was metabolized, carbohydrates were preferential carbon sources for these actinomycetes. A spore-containing soluble dry powder formulation was used as an inoculum in an in situ field experiment. This formulation was maintained in storage at 4°C for over two years without viability loss. Results from the golf green experiment showed that although treated thatch layers in established greens were not appreciably reduced over the course of one summer, theStreptomyceswere active and maintained their populations within the thatch, while fungal growth was suppressed as compared to controls. The results show that treatment of turfgrass with theseStreptomycesmay be useful for the long-term control of fungal populations within the thatch. Longer field studies are required to assess the long-term potential for also controlling thatch build-up and fungal pathogens.Key words: biocontrol, biodegradation, fungi,Streptomyces, thatch

ISSN:0008-4166    

DOI:10.1139/w00-025

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The main purpose of this work was to study the microbiology of the Hungarian Upper Permian Siltstone (Aleurolite) Formation, to assess the safety of future underground repositories for nuclear waste. Sixty-seven air, groundwater, technical water, rock, and surface samples were collected aseptically from different depths. The number of aerobic and anaerobic isolates was 277. The mesophilic minimum and maximum CFU counts of the air samples were 1.07-5.84 × 102·mL-1(aerobic) and 0.22-1.04 × 102·mL-1(anaerobic), respectively; those of the water samples were 0.39-1.25 × 105·mL-1(aerobic) and 0.36-3.9 × 103·mL-1(anaerobic); those of the technical water samples were 0.27-5.03 × 106·mL-1(aerobic) and 4 × 105- >106·mL-1(anaerobic); and those of the aleurolite samples were 2.32 × 102- 2.47 × 105·g-1(aerobic) and 0.45-9.5 × 102·g-1(anaerobic). In the groundwater, the thermophilic aerobic bacteria count was 0-2.4 × 102·mL-1and the thermophilic anaerobic bacteria count was 0.43-4.6 × 104·mL-1. The gases produced by the 16 gas-forming isolates were CO2(aerobic isolates), and CO2and H2(anaerobic isolates). About 20% of the aerobic isolates produced siderophores. The proportions of organic acid producers were lowest in aerobic and anaerobic isolates from the aleurolite, 13% and 14%, respectively. The highest proportions of acid producers in the aerobic and anaerobic isolates from the air samples were 63% and 54%. Altogether 160 of the aerobic isolates and 52 of the anaerobic isolates were spore formers. The radiosensitivity of the aerobic isolates was also determined; the D10values of the sporeformers ranged between 0.8-2.44 kGy. Our results indicate that the sulfate-reducing bacteria and the production of complexing agents (siderophores) may contribute to the mobilization of radionuclides from underground repositories. As well, microbial gas production can influence the environmental conditions. The variability in bacterial radiotolerance indicates the biodiversity at this potential disposal site. These facts must be considered during the planning of a nuclear waste repository.Key words: nuclear waste disposal, microbial gas production, siltstone formation, siderophore production, radios

ISSN:0008-4166    

DOI:10.1139/w00-020

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A 300-km portion of the Saint Lawrence hydrological basin in the province of Québec (Canada) and 45 water treatment plants were studied. River water used by drinking water treatment plants was analyzed (6-L sample volumes) to determine the level of occurrence of bacterial indicators (total coliforms, fecal coliforms, andClostridium perfringens) and pathogens (Giardia lamblia,Cryptosporidium, human enteric viruses). Pathogens and bacterial indicators were found at all sites at a wide range of values. Logistic regression analysis revealed significant correlations between the bacterial indicators and the pathogens. Physicochemical and treatment practices data were collected from most water treatment plants and used to estimate the level of removal of pathogens achieved under cold (0°C-4°C) and warm (20°C-25°C) water temperature conditions. The calculated removal values were then used to estimate the annual risk ofGiardiainfection using mathematical models and to compare the sites. The estimated range of probability of infection ranged from 0.75 to less than 0.0001 for the populations exposed. Given the numerous assumptions made, the model probably overestimated the annual risk, but it provided comparative data of the efficacy of the water treatment plants and thereby contributes to the protection of public health.Key words: public health, drinking water, health risk, pathogen occurr

ISSN:0008-4166    

DOI:10.1139/w00-022

出版商:NRC Research Press    

年代:2000

数据来源: NRC