摘要:

Metabolic activities and toxicity of the dinoflagellateAlexandrium tamarensewere studied for a dialysis culture exposed to unenriched natural seawater and a batch culture grown in an enriched medium. The following observations were made on the dialysis culture compared with the batch culture: (i) Depending on the season period, the cell densities per litre were similar (≈ 10 × 106– 14 × 106) or greater (66 × 106). (ii) During growth and stationary phases, cellular consumption of the nutrients (NO3− + NO2−) was much greater (5–50 times), (iii) During growth, the composition of the intracellular (IFAA) and extracellular dissolved free amino acid (EFAA) was characterized by the presence of ORN and LYS in the dialysis culture, which represent a substantial fraction of the IFAA pool of the dinoflagellate; a significant depletion of the IFAA was observed, but the recovery of Gln, Glu, and Arg cell concentration levels at the stationary phase was more important. (iv) During the growth phase, the maximum excretion rate of amino acids (fmol∙cell−1∙d−1) was 263 (in decreasing order of importance: Glu, Gin, Ser, Asp, Leu, Ala, G+T, and Orn) compared with 14,5. (v) During stationary phase, the reduction in excretion activity was twofold with Gln, Glu, Leu, and Orn while 9,2 fmol∙cell−1∙d−1were observed in batch culture, (vi) Total toxin content was about 4 to 5 times higher (means: 95 and 75 fmol∙cell−1during growth and stationary phases respectively), with greater concentrations in more potent derivates like saxitoxin and neosaxitoxin. This higher cell toxicity may be attributed to the particular growth conditions of the dialysis culture, which more closely approximate the natural environment, through diffusion processes involving a constant elimination of low molecular weight autoinhibitory metabolites and a more efficient nutrient uptake.Key words:Alexandrium tamarense, dinoflagellate, dialysis culture, phycotoxins, nitrogen

ISSN:0008-4166    

DOI:10.1139/m97-043

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The hyaluronate lyase (hyaluronidase) gene fromPropionibacterium acneswas cloned and sequenced. The gene was isolated on anEcoRI-generated 3-kb piece of DNA. Expression was less inEscherichia colithan inP.acnes; inE.coli, active enzyme was only cell associated and not secreted. The gene is 2256-bp long and codes for a protein of 82 kDa. Amino terminal sequencing of the protein of the partially purified gene indicated the presence of a 32-amino-acid leader sequence. The leader sequence showed a membrane-spanning domain and all of the features usually associated with the leader for a secreted protein. The amino acid sequence is predicted to share homology with the hyaluronidase enzymes fromStreptococcus pneumoniae,Streptococcus agalactiae, andStaphylococcus aureus. A potential hyaluronate-binding domain was identified and antibody against this domain was inhibitory to the enzyme.Key words:Propionibacterium acnes, hyaluronidase, leader sequence, hyaluronate binding domain, sequence homology among hyaluronidases.

ISSN:0008-4166    

DOI:10.1139/m97-044

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Chitinases are produced byMetarhizium anisopliaewhen it is grown in the presence of chitin. A chitinase from the culture filtrate ofMetarhizium anisopliaewas successively purified by precipitation with ammonium sulphate, followed by anion-exchange chromatography on DEAE-Sephacel. The purified enzyme, which has a molecular mass of approximately 30 kDa by sodium dodecyl sulphate – polyacrylamide gel electrophoresis, catalyses the hydrolysis ofp-nitrophenyl β-N-diacetylchitobiose with an apparentKmof 0.537 mmol andVmaxof 4.86 nmol∙mL−1∙min−1. The optimum pH and temperature were 4.5–5.0 and 40–45 °C, respectively.Key words: chitinases,Metarhizium anisopliae, enzyme purification, enzyme characterizat

ISSN:0008-4166    

DOI:10.1139/m97-045

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The presence of killer and proteolytic yeasts was studied among 944 isolates representing 105 species from tropical yeast communities. We found 13 killer toxin producing species, withPichia kluyveribeing the most frequent. Other killer yeast isolates wereCandida apis,Candida bombicola,Candida fructus,Candida krusei,Candida sorbosa,Hanseniaspora uvarum,Issatchenkia occidentalis,Kloeckera apis,Kluyveromyces marxianus,Pichia membranaefaciens,Pichia ohmeri-like, andSporobolomyces roseus. The communities from which killer yeasts were isolated had strains sensitive to them, and there were interspecific and intraspecific differences in the spectra of their killer activities.Pichia kluyverihad the broadest spectra of activity against sensitive isolates, and it apparently produced different toxins. The coexistence of sensitive and killer yeasts using the same substrate suggests that there is spatial separation in microhabitats or temporal separation in different stages of successions. Basidiomycetous yeasts were more frequently proteolytic than ascomycetous yeasts. Extracellular proteases could be important for the yeasts to have access to more nitrogen nutrients and obtain a better balance with available carbon sources.Key words: killer yeasts, extracellular proteases, tropical yeast communities.

ISSN:0008-4166    

DOI:10.1139/m97-046

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A screening programme to isolate new strains of the entomopathogenic bacteriaBacillus thuringiensiswas undertaken on 4887 samples of various sources from 101 countries over the world: 1260 strains of the bacillus were isolated. Dust from mills and silos, as well as insects from nature, were more successful sources than soil samples, which emphasizes the diversity of biotopes where the bacillus is encountered. Electrophoretic characterization reveals the genetic variability of the species. An analysis of insecticidal properties of the isolated strains was performed on four insect species:Plutella xylostella(Lepidoptera: Plutellidae),Spodoptera littoralis(Lepidoptera: Noctuidae),Phaedon cochleariae(Coleoptera: Chrysomelidae), andLocusta migratoriaorSchistocerca gregaria(Orthoptera: Acrididae). The most frequent strains (54%) were producing crystals constituted of proteins with molecular masses of 130–140 or 66 and 130–140 kDa and were toxic to Lepidoptera larvae. A significant number of strains (31) were larvicidal to Coleoptera while only one, H14 serotype, was active on Diptera. Numerous strains synthesize crystals made up of proteins with size differing from the already known toxins. Most of these strains were nonactive against the four insect species tested. One strain showing a protein band at 73 kDa had no insecticidal activity againstP.cochleariaewhile it was toxic toP.xylostella.Key words:Bacillus thuringiensis, new strains, distribution, Lepidoptera, Coleoptera.

ISSN:0008-4166    

DOI:10.1139/m97-047

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The future use of genetically modified microorganisms in the environment will be dependent on the ability to assess potential or theoretical risks associated with their introduction into natural ecosystems. To assess potential risks, several ecological parameters must be examined, including the impact of the introduced genetically modified organism on the microbial communities associated with the environment into which the introduction will occur. A 2-year field study was established to examine whether the indigenous bacterial communities of the rhizosphere and endorhiza (internal root tissues) were affected differently by the introduction of an unaltered wild type and its genetically modified derivative. Treatments consisted of the wild-type strainPseudomonas fluorescens89B-27 and a bioluminescent derivative GEM-8 (89B-27::Tn4431). Cucumber root or seed samples were taken 0, 7, 14, 21, 35, and 70 days after planting (DAP) in 1994 and 0, 7, 14, 28, 42, and 70 DAP in 1995. Samples were processed to examine the bacterial communities of both the rhizosphere and endorhiza. Over 7200 bacterial colonies were isolated from the rhizosphere and endorhiza and identified using the Sherlock System (Microbial ID, Inc.) for fatty acid methyl ester analysis. Community structure at the genus level was assessed using genera richness and Hill's diversity numbers,N1 andN2. The aerobic–heterotrophic bacterial community structure at the genus level did not significantly vary between treatments but did differ temporally. The data indicate that the introduction of the genetically modified derivative of 89B-27 did not pose a greater environmental risk than its unaltered wild type with respect to aerobic–heterotrophic bacterial community structure.Key words: diversity, ecology, PGPR,Pseudomonas, root colonizaton, GEM.

ISSN:0008-4166    

DOI:10.1139/m97-048

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The effects of inoculum density (0, 4.6 × 107, 4.2 × 108, and 8.8 × 108 cfu∙mL−1), temperature (10, 20, and 30 °C), and plant genotype (cultivars Celebrity, Blazer, Scotia, and Mountain Delight) on bacterial colonization and plant growth promotion were investigated in a gnotobiotic system. An in vitro dual culture of tomato (Lycopersicon esculentumL.) plantlets and aPseudomonassp., strain PsJN, were used. Epiphytic (external) and endophytic (internal) bacterial populations were determined to evaluate plantlet colonization. Shoot and root biomass of bacterized plantlets was significantly higher (p ≤ 0.05) than that of nonbacterized controls. Growth promotion was best with inoculum densities of 3 × 108– 7 × 108 cfu∙mL−1at 20 °C, particularly in the early maturing cultivars Blazer and Scotia. Lower inoculum densities were required to maximize root growth (approximately 1 × 108 cfu∙mL−1) than shoot growth (approximately 3 × 108 cfu∙mL−1). Shoot surface populations did not vary with inoculum density or temperature, but the bacterium colonized the shoot exterior of cultivars Celebrity, Mountain Delight, and Scotia better than cultivar Blazer. The root surface populations increased linearly with increasing inoculum density (within a range of 107–108 cfu∙mL−1), decreased with increasing temperatures (from 10 to 30 °C), and were higher for the main season cultivar Celebrity than for cultivars Blazer, Scotia, and Mountain Delight. Populations of shoot endophytes did not vary with initial inoculum density or genotype but were affected by temperature; the highest colonization was at 10 °C. The number of root endophytes was also highest at 10 °C at the inoculum density of approximately 4 × 108 cfu∙mL−1and did not vary with genotypes. The experiments clearly indicate that there was no relationship between root surface colonization and plant growth promotion. However, the range of inoculum levels (3 × 108– 7 × 108 cfu∙mL−1) that promoted colonization of the inner root tissues (endophytic) also best promoted plant growth. A possible biostimulation threshold within the tissues of the inoculated plants under conditions favourable to the growth of tomato is proposed.Key words:Pseudomonassp., tomato, colonization, gro

ISSN:0008-4166    

DOI:10.1139/m97-049

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Microflora in wound sites of preharvest maize (including bacteria, yeasts, and filamentous fungi) may play a role in attracting insects to maize plants and may also interact with growth and mycotoxin production by filamentous fungi. As little data are available about the yeasts occurring on maize from the U.S. corn belt, samples of milled maize from experimental plantings at the University of Illinois River Valley Sand Field were analyzed. Yeast counts showed slight yearly fluctuation and varied between 3.60 and 5.88 (log cfu/g maize). The majority of the yeasts wereCandida guilliermondii(approximately 55%),Candida zeylanoides(24 %),Candida shehatae(11%), andDebaryomyces hansenii(3%). Also present wereTrichosporon cutaneum,Cryptococcus albidusvar.aerius, andPichia membranifaciens. The occurrence of killer yeasts was also evaluated. Killer yeasts were detected in maize for the first time and were identified asTrichosporon cutaneumandCandida zeylanoides. These were able to kill some representative yeasts isolated from maize, includingCandida guilliermondii,Candida shehatae, andCryptococcus albidusvar.aerius. Other maize yeasts (Candida zeylanoides,Debaryomyces hansenii,Pichia membranifaciens) were not affected. The majority of yeasts found on maize were unable to ferment its major sugars, i.e., sucrose and maltose. Some (e.g.,Candida zeylanoides) were not even able to assimilate these sugars. The importance of these properties in relation to insect attraction to preharvest ears of maize is discussed.Key words: corn, maize, yeast, killer.

ISSN:0008-4166    

DOI:10.1139/m97-050

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Five polycyclic aromatic hydrocarbon (PAH) degrading bacterial strains,Pseudomonas putida34,Pseudomonas fluorescens62,Pseudomonas aeruginosa57,Sphingomonassp. strain 107, and the unidentified strain PL1, were isolated from two contaminated soils and characterized for specific features regarding PAH degradation. Degradation efficiency was determined by the rapidity to form clearing zones around colonies when sprayed with different PAH solutions and the growth in liquid medium with different PAHs as sole source of carbon and energy. The presence of plasmids, the production of biosurfactants, the effect of salicylate on PAH degradation, the transformation of indole to indigo indicating the presence of an aromatic ring dioxygenase activity, and the hybridization with the SphAb probe representing a sequence highly homologous to the naphthalene dioxygenase ferredoxin genenahAbwere examined. The most efficient strain in terms of substrate specificity and rapidity to degrade different PAHs wasSphingomonassp. strain 107, followed by strain PL1 andP.aeruginosa57. The less efficient strains wereP.putida34 andP.fluorescens62. Each strain transformed indole to indigo, except strain PL1. Biosurfactants were produced byP.aeruginosa57 andP.putida34, and a bioemulsifier was produced bySphingomonassp. strain 107. The presence of salicylate in solid medium has accelerated the formation of clearing zones and the transformation of indole bySphingomonassp. strain 107 andP.aeruginosa57 colonies. Plasmids were found inSphingomonassp. strain 107 and strain PL1. The SphAb probe hybridized with DNA extracted from each strain. However, hybridization signals were detected only in the plasmidic fraction ofSphingomonassp. strain 107 and strain PL1. Using a polymerase chain reaction (PCR) approach, we determined that several genes encoding enzymes involved in the upper catabolic pathway of naphthalene were present in each strain. Sequencing of PCR DNA fragments revealed that, for all the five strains, these genes are highly homologous with respective genes found in thepah,dox, andnahopérons, and are arranged in a polycistronic operon. Results suggest that these genes are ordered in the five selected strains like thepah,nah, anddoxopérons.Key words: polycyclic aromatic hydrocarbons, biodegradation, polymerase chain reaction, naphthalene catabolic genes.

ISSN:0008-4166    

DOI:10.1139/m97-051

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The transformation of pentachlorophenol (PCP) byPhanerochaete chrysosporiumI-1512 in relation to pentachloroanisole (PCA) was studied in two different modes of culture. The degradation of PCP by immobilized cells in agitated medium was compared with that by static cultures. Results clearly established the advantage of an immobilized culture for mineralization of PCP: 23% of CO2released for fungus immobilized on stainless steel mesh rings as compared with 11% for static cultures. PCA, a metabolite of PCP, was formed only in static cultures and underwent a limited mineralization. Moreover, experiments performed with mycelium and culture supernatant (in the presence of cycloheximide) clearly demonstrated that PCA formation was catalyzed by the biomass in static cultures ofP.chrysosporium. Assays in vitro did not establish any involvement of lignin or manganese peroxidases in PCP or PCA transformation.Key words: filamentous fungi,Phanerochaete chrysosporium, pentachlorophenol, pentachloroanisole.

ISSN:0008-4166    

DOI:10.1139/m97-052

出版商:NRC Research Press    

年代:1997

数据来源: NRC