摘要:

We studied the population biology of the nematophagous fungusHirsutella rhossiliensisto understand its potential as a biological control agent. Because the fungus is an infectious and transmissible parasite, we framed our study within an epidemiological context. Field observations, theory, and experiments demonstrated that (i) parasitism of nematodes byH.rhossiliensisis dependent on nematode density, (ii) local populations of the fungus will go extinct unless supplied with some minimum number of nematodes (the host threshold density), and (iii) natural epidemics of this fungus in populations of nematodes develop slowly and only after long periods of high host density. Additional in-depth research on population biology is needed to explain other biological control systems and to guide future research. The most effective research will combine field observation, theory, and experimentation.Key words: density-dependent parasitism, host-parasite dynamics, modeling, nematophagous fungi.

ISSN:0008-4166    

DOI:10.1139/m92-061

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The techniques in current use for detection of pathogens in environmental samples are restricted to those organisms whose replication in either culture media or cell culture is feasible. These methods lack the selectivity and sensitivity necessary for their unequivocal detection and identification. We have developed an assay for the detection of bacterial cells in large volumes of water. Low concentrations of cells containing target sequences were concentrated on membrane filters and were subjected to amplification directly using a stepwise polymerase chain reaction. This procedure, together with nucleic acid probes, has enhanced the limit of detection to the level of a single bacterial cell. This technique could be used for the detection of any bacteria or virus in water or air.Key words: polymerase chain reaction, waterborne pathogens, water.

ISSN:0008-4166    

DOI:10.1139/m92-062

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Prevotella(Bacteroides)ruminicolastrains B14 and S23 andSelenomonas ruminantiumstrain D used xylose as the sole source of carbohyrate for growth, whereasFibrobacter succinogeneswas unable to metabolize xylose.Prevotella ruminicolastrain B14 exhibited transport activity for xylose. In contrast,F.succinogeneslacked typical xylose uptake activity but did exhibit low binding potential for the sugar.Prevotella ruminicolastrains B14 and S23 as well asS.ruminantiumD showed low xylose isomerase activities but higher xylulokinase activities, using assays that gave high activities for these enzymes inEscherichia coli. Xylose isomerase appeared to be produced constitutively in these ruminal bacteria, but xylulokinase was induced to varying degrees with xylose as the source of carbohydrate.Fibrobacter succinogeneslacked xylose isomerase and xylulokinase. All three species of ruminal bacteria possessed transketolase,xylulose-5-phosphate epimerase, and ribose-5-phosphate isomerase activities. NeitherP.ruminicolaB14 norF.succinogenesS85 showed significant phosphoketolase activity. The data indicate thatF.succinogenesis unable to either actively uptake or metabolize xylose as a result of the absence of functional xylose permease, xylose isomerase, and xylulokinase activities, although it and bothP.ruminicolaandS.ruminantiumpossess the essential enzymes of the nonoxidative branch of the pentose phosphate cycle.Key words:Fibrobacter succinogenes,Prevotella,Selenomonas, xylose metabolism, rumen bacteria, pentose phosphate cycle.

ISSN:0008-4166    

DOI:10.1139/m92-063

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Several probes were used in this ultrastructural study to localize polysaccharides in cell walls on conidial germ tubes, hyphal bodies, and mycelia of the entomogenous hyphomyceteNomuraea rileyi. With the exception of galactose, labelling patterns did not vary from one morphological stage to another. Galactose, which was localized by using a monoclonal antibody to a galactose-specific lectin purified from insect larval hemolymph, was absent from cell walls of hyphal bodies and conidia but was present on germ-tube and mycelial surfaces. Chitin (N-acetylglucosamine), labelled with a wheat-germ agglutinin-ferritin conjugate, was present in the middle regions of lateral walls and septa, and β1-4 glucans were located in the middle and inner regions, as indicated by binding of a cellulase-gold conjugate. An anti-laminaribiose antibody was used to label β1-3 glucans present in the outer wall areas and inner regions near the plasmalemma. The location of mannose residues as indicated by concanavalin A - ferritin binding was similar to that of the β1-3 glucans; vesicle-like structures were also labelled. None of the probes labelled the outer conidial pellicle or exocellular sheath surrounding germ tubes, and labelling of mycelial sheath was inconsistent. The absence of galactose fromNomuraeahyphal body walls is discussed in terms of host-parasite interaction.Key words:Nomuraea rileyi, entomopathogenic fungi, glycoconjugates, lectins, monoclonal antibodies.

ISSN:0008-4166    

DOI:10.1139/m92-064

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Two techniques, electroporation and conjugation, have been used to introduce the RK2-based broad-host-range plasmids pRK415 and pLAFR3 into strains of the bacterial genusAcidiphilium. Using electroporation, cells were also transformed with a series of chimeric plasmids constructed by cloning crypticAcidiphiliumplasmids into theEscherichia colivector pBR328. Various parameters affecting electroporation were investigaed. Transformation efficiency varied widely with different recipient strains. Growth at an elevated temperature (37 °C) prior to electroporation increased transformation efficiency 10-fold compared with growth at 32 °C. For three strains tested, optimum transformation efficiency was obtained with field strengths of 10–15 kV/cm. Transformation efficiency increased linearly with increasing DNA concentration up to 10 μg/mL. Transformation efficiencies in these experiments ranged up to 104transformants/μg DNA. Mobilization of pRK415 and pLAFR3 fromE.colistrain S17.1 into severalAcidiphiliumstrains was achieved following incubation for 3 h on nutrient agar medium (pH 7.0). Conjugation frequencies in the range of 10−5–10−9per recipient cell were obtained. Conjugation frequency was also dependent on recipient strain.Key words: acidophilic bacteria, endogenous plasmids, broad-host-range plasmids.

ISSN:0008-4166    

DOI:10.1139/m92-065

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A new bacterial disease of a cultivated mushroom,Agaricus bitorquis, is reported. Symptoms exhibited by affected sporocarps range from mild blotching to deep pitting, where large pervasive cavities extending from the cap surface to the stipe may form. Sporocarps often show a characteristic eroded appearance where the tissues are completely degraded. Some areas of diseased sporocarps fail to show any external symptoms, but on cutting the cap, massive breakdown of the underlying tissue is evident, resulting in a hollow cap. The causal bacterium, confirmed by application of Koch's postulates, is a nonfluorescent pseudomonad identified asPseudomonas cepacia.Key words:Pseudomonas cepacia,Agaricus bitorquis, tissue degradation, cavities.

ISSN:0008-4166    

DOI:10.1139/m92-066

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Lactococcus lactisssp.cremorisC3 was shown to contain two prophages, C3-T1 and C3-T2, both inducible bymitomycin C. The phages were morphologically indistinguishable, having an isometric head (55 nm), a noncontractile tail (142 nm), and a distinctive base plate. The phages C3-T1 and C3-T2 were differentiated from one another by restriction endonuclease analysis of their DNA, and genome sizes of 37.8 (C3-T1) and 32.5 kb (C3-T2). Southern blot DNA hybridization suggested a maximum homology between the phage genomes of 50%. Phage C3-T1 was propagated and the phage obtained was designated C3-TIℓ. Phage C3-T2 was not propagated despite tests with a large number of possible indicator strains. Restriction enzyme analysis of phage C3-T1ℓ genome yielded a 37.8-kb circular restriction map. The packaging site (pac) and site of integration into the bacterial chromosome (att) were located and anEcoRI DNA fragment containing theattsite was cloned. Only one C3-T1attsite was present in the C3 chromosome. No homology was detected between DNA from C3-T1ℓ and DNA from lytic phages commonly isolated from cheese wheys.Key words: lactococcal phages, temperate phages, lysogeny, evol

ISSN:0008-4166    

DOI:10.1139/m92-067

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Flocculation of some yeasts involves lectinlike receptors with two different patterns of inhibition by sugars: mannose sensitive (MS) and glucose-mannose sensitive (GMS). The visualization and quantification of these receptors were performed using neoglycoproteins fluorescent probes. Fluorescence microscopy showed a homogeneous distribution of surface receptors for the strain belonging to the MS group and a polar distribution for cells belonging to the GMS group. Affinity constants, estimated by fluorimetry, were shown to have different values (MS, 2.6 ± 0.7 × 105 M−1; GMS, 2 ± 1 × 106 M−1), but the number of sites was estimated to be smaller for strain NCYC 1195 which belongs to the GMS group than for strain NCYC 869 from the MS group (MS, 2.4 ± 0.2 × 107 sites/cell; GMS, 3.9 ± 0.8 × 106 sites/cell).Key words: flocculation, neoglycoproteins,Saccharomyces, lectinlike.

ISSN:0008-4166    

DOI:10.1139/m92-068

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Alkaline phosphatase conjugated oligonucleotide probes were developed to detect the genes (tdhandtrh) coding for the thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) ofVibrio parahaemolyticus. Using dot blot hybridization, probes were tested with 94 clinical isolates ofV.parahaemolyticus. Results agreed well with those obtained using radio-labeled recombinant DNA probes for the genestdhandtrh. Specificity and sensitivity of enzymetdhprobes for detection of thetrhgene were 100 and 93%, respectively, and those of thetrhprobes fortrhgene detection were 93 and 86%, respectively. Thetdhprobes also hybridized withtdh-like genes processed by all strains ofV.hollisae, and some strains ofV.mimicusandV.choleraenon-O1, but neithertdhnortrhprobes reacted with other bacterial species isolated from diarrheal stools. However, someV.parahaemolyticusstrains that were negative with the enzymetrhprobe hybridized weakly with a radio-labeledtrhDNA fragment probe at medium stringency, and a few strains that were negative in high stringency conditions with a radio-labeledtrhDNA fragment probe hybridized with the enzymetrhprobe. This suggests that some strains ofV.parahaemolyticusmay carry another gene resemblingtrh.Key words: oligonucleotide DNA, enzyme,Vibrio parahaemolyticus, hemolysin.

ISSN:0008-4166    

DOI:10.1139/m92-069

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The yeastPichia stipitis, strain NRC 5568, when grown onL-rhamnose as sole carbon source produced an NAD+-dependentL-rhamnose dehydrogenase enzyme, which is repressed byD-glucose. Mutants defective in carbon catabolite repression were isolated, using a selective medium containing 2-deoxy-D-glucose. Six of eight mutants resistant to 2-deoxy-D-glucose showedL-rhamnose dehydrogenase synthesis insensitive toD-glucose repression. All eight mutants, named PR mutants, as well as the parent strain, were found to grow onD-glucose,L-rhamnose, and glycerol. In addition, they were all capable of growing on 2-deoxy-D-glucose as sole carbon source,D-Glucose and 2-deoxy-D-glucose caused almost complete inhibition ofL-rhamnose dehydrogenase synthesis in the wild-type strain but only a slight decrease in the enzyme synthesis in the mutant strain PR1. The wild-type and mutant strains showed the same pattern of inhibition by cycloheximide, 8-hydroxyquinoline, and benomyl.Key words:Pichia stipitis,L-rhamnose dehydrogenase, catabolite-resistant mutant, 2-deoxy-D-glucose.

ISSN:0008-4166    

DOI:10.1139/m92-070

出版商:NRC Research Press    

年代:1992

数据来源: NRC