摘要:

To investigate whether leaf-surface yeasts adhere to the phylloplane in a two-phase manner, with weak, nonspecific attachment followed by stronger, time-dependent adhesion, we observed adhesion kinetics of the basidiomycete yeastRhodosporidium toruloidesto barley. While 50-60% of the cells adhered in short-term assays (up to 3 h), fewer than 10% were adherent after 10 days. Ten attachment-minus (Att-) mutants, deficient in phase I attachment, did not adhere after 5-day incubations, further suggesting a lack of stronger, independent phase II adhesion. Long-term (5 day) adhesion was similar for two isolates ofR. toruloidesand the ubiquitous leaf-surface fungusAureobasidium pullulans. Long-term adhesion ofR. toruloidesto leaves of a waxless barley mutant was significantly greater than to leaves of the wild-type cv. Bonus. Application of exogenous nutrients (dilute yeast carbon base) to resident, wild-typeR. toruloidespopulations resulted in both a rapid recolonization to the apparent carrying capacity of the leaves and an increase in the total adherent populations. Att-mutants recolonized barley segments, when supplied with nutrients, after more than 99% of the cells had been removed by agitation. Therefore, adhesion ofR. toruloidesto leaves was not required for subsequent colonization of the phylloplane. Overall, these data suggest that the frequency of yeast emigration from leaf surfaces, microbial growth rates, and leaf surface characteristics are major factors influencing colonization of leaf surfaces.Key words: epiphyte, phylloplane,Rhodotorula glutinis.

ISSN:0008-4166    

DOI:10.1139/w99-022

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Survival and development of cactus transplants in urban, disturbed areas of the desert near La Paz, Baja California Sur, Mexico, was monitored. Young plants of three species of pachycereid cacti (Pachycereus pringlei,Stenocereus thurberi, andLophocereus schottii) inoculated with the plant growth promoting bacteriumAzospirillum brasilensein an eroded area (a dirt road) had a high survival rate and developed more rapidly compared with uninoculated control plants during a 3.5-year period after transplantation. Soil erosion in the inoculated experimental area diminished. Small, but significant soil accumulated in association with the growth of cactus roots into the wind-deposited dust. One demonstrated mechanism for stabilizing dust was by the upward growth of small roots during the rainy season into the deposited dust.Azospirillum brasilensesurvived well in the rhizospheres of these cacti for 2 years, but not in root-free soil. This study demonstrated the feasibility of using bacterial inoculation of cacti to enhance their establishment in disturbed areas, with the potential to stabilize soil.Key words:Azospirillum, beneficial bacteria, cactus, plant inoculation, plant growth promoting bacteria, PGPR, soil erosion, soil reclamation.

ISSN:0008-4166    

DOI:10.1139/w99-043

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A total of 59 bacteria samples from Antarctic sea water were collected and screened for their ability to produce &agr;-amylase. The highest activity was recorded from an isolate identified as anAlteromonasspecies. The purified &agr;-amylase shows a molecular mass of about 50 000 Da and a pI of 5.2. The enzyme is stable from pH 7.5 to 9 and has a maximal activity at pH 7.5. Compared with other &agr;-amylases from mesophiles and thermophiles, the "cold enzyme" displays a higher activity at low temperature and a lower stability at high temperature. The psychrophilic &agr;-amylase requires both Cl-and Ca2+for its amylolytic activity. Br-is also quite effecient as an allosteric effector. The comparison of the amino acid composition with those of other &agr;-amylases from various organisms shows that the cold &agr;-amylase has the lowest content in Arg and Pro residues. This could be involved in the principle used by the psychrophilic enzyme to adapt its molecular structure to the low temperature of the environment.Key words: &agr;-amylase, psychrophilic microorganisms, Antarctic.

ISSN:0008-4166    

DOI:10.1139/w99-021

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The metabolism of cresols under sulfate-reducing conditions was investigated inDesulfotomaculumsp. strain Groll. This strain grows on a variety of aromatic compounds, includingpara- andmeta- but notortho-cresol. Degradation ofp-cresol proceeded by oxidation reactions of the methyl group to yieldp-hydroxybenzoate, which was then dehydroxylated to benzoate. The aromatic intermediates expected for this pathway,p-hydroxybenzyl alcohol,p-hydroxybenzaldehyde,p-hydroxybenzoate, and benzoate, were readily metabolized by strain Groll. Utilization of these intermediates generally preceded and inhibited the degradation ofp-cresol.p-Hydroxybenzoate and benzoate were detected in culture fluid as metabolites ofp-cresol.p-Hydroxybenzaldehyde andp-hydroxybenzoate were detected in cultures degradingp-hydroxybenzyl alcohol. Enzyme activities responsible for utilization ofp- andm-cresol, induced by growth on the respective cresol, were detected in cell-free extracts of strain Groll. The compounds detected in culture fluids and the enzyme activities detected in cell-free extracts indicate that the pathways for the degradation ofp- andm-cresol converge on benzoate, followed by metabolism to benzoyl-coenzyme A (CoA). Strain Groll can utilize both cresol isomers under sulfate-reducing conditions by similar reactions, but the enzyme activities catalyzing these transformations of the two isomers appear distinct.Key words: anaerobic biodegradation, sulfate reduction,Desulfotomaculum,p-cresol,m-cresol,o-cresol, benzoylCoA.

ISSN:0008-4166    

DOI:10.1139/w99-041

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A Brazilian strain ofBacillus thuringiensissubsp.kurstaki, designated S93, was analyzed regarding itscrygene and protein contents and activity against the fall armyworm (Spodoptera frugiperda, Smith 1797). Bioassays using lyophilized powders of S93 or HD-1 and third instar larvae ofS. frugiperdashowed a 12.3-fold lower LC50for the S93 strain when compared with the standard HD-1 strain. The spore-crystal mixture, analyzed by SDS-PAGE, showed two major polypeptides of 130 and 65 kDa, corresponding to Cry1 and Cry2 toxins, respectively. Western blot analysis showed that these proteins were immunologically related to the Cry1A protein fromB. thuringiensissubsp.kurstakiHD-73. The polymerase chain reaction technique (PCR) using total DNA from the S93 strain and specific primers showed the presence ofcry1Aa,cry1Ab, andcry1Acgenes, and acry1A-type gene was localized in a plasmid of about 44 MDa. Acry1Abgene was isolated from a S93 plasmid DNA library and completely sequenced. Computer analysis showed that the gene sequence (GenBank acession number AF059670) is identical tocry1Ab1and has 91.6 and 85.9% identity withcry1Aa1andcry1Ac1genes, respectively. The deduced amino-acid sequence showed a high degree of similarity with the amino-acid sequences of the Cry1Ab1 (100%), Cry1Aa1 (93.8%), and Cry1Ac1 (90.6%) proteins.Key words:Bacillus thuringiensis,Spodoptera frugiperda, biological control, crystal protein,crygenes.

ISSN:0008-4166    

DOI:10.1139/w99-032

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The response of a yeast unsaturated fatty acid auxotroph, defective in &Dgr;9-desaturase activity, to heat and ethanol stresses was examined. The most heat- and ethanol-tolerant cells had membranes enriched with oleic acid (C18:1), followed in order by cells enriched with linoleic (C18:2) and linolenic (C18:3) acids. Cells subjected to a heat shock (25-37°C for 30 min) accumulated trehalose and synthesized typical heat shock proteins. Although there were no obvious differences in protein profiles attributable to lipid supplementation of the mutant, relative protein synthesis as determined by densitometric analysis of autoradiograms suggested that hsp expression was different. However, there was no consistent relationship between the synthesis of heat shock proteins and the acquisition of thermotolerance in the lipid supplemented auxotroph or related wild type. Furthermore, trehalose accumulation was also not closely related to stress tolerance. On the other hand, the data presented indicated a more consistent role for membrane lipid composition in stress tolerance than trehalose, heat shock proteins, or ergosterol. We suggest that the sensitivity of C18:3-enriched cells to heat and ethanol may be attributable to membrane damage associated with increases in membrane fluidity and oxygen-derived free radical attack of membrane lipids.Key words: stress tolerance, yeast lipid mutant, membrane lipid unsaturation, trehalose, heat shock proteins

ISSN:0008-4166    

DOI:10.1139/w99-033

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In order to facilitate further investigation of Rev function, we have generated two systems for the inducible expression of Rev in mammalian cell lines (HeLa and U937) using either a tetracycline-regulated promoter or fusion of Rev to a modified form of the hormone binding domain of the estrogen receptor. In the case of the fusion of Rev to the modified hormone binding domain of the estrogen receptor, we demonstrated induction of Rev function in response to tamoxifen administration to levels comparable to that of the unmodified Rev protein. Subsequently, U937 lines were generated that retained the observed pattern of hormone-dependent function of the Rev fusion protein. In the case of the tetracycline-regulated system, cell lines (both HeLa and U937) were generated that displayed tight regulation of Rev. In the case of the HeLa cell lines, they were used for the subsequent generation of stable cell lines expressing either HIV-1envor chloramphenicol acetyl transferase (CAT) in a Rev-dependent fashion. Using the latter cell lines, we demonstrate the ability to control Rev expression over a broad concentration range and find that, as soon as Rev expression is detectable, induction of Rev-dependent gene expression is also observed.Key words: Rev, tamoxifen, tetracyline-regulated transcription, Rev function, threshold effects.

ISSN:0008-4166    

DOI:10.1139/w99-011

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The utilization of low molecular weight aromatic compounds implies the operation of complex metabolic pathways. In order to investigate the taxonomic relevance of this property among heterobasidiomycetous yeasts, both at the species level and at higher taxonomic ranks, the capacity to assimilate twenty such compounds was tested in a total of 332 strains representing approximately 200 species. The substrates most frequently utilized were protocatechuic, caffeic, andp-hydroxybenzoic acids, whereas cinnamic, sinapic, and syringic acids and guaiacol were never assimilated. The assimilation of the majority of the aromatic compounds investigated correlated with the utilization of protocatechuic acid. Among the Urediniomycetes, the members of the Sporidiales and those of theNaohidea-Rhodotorula minutaclade showed a good ability to utilize aromatic compounds, whereas the members of theAgaricostilbum-Kondoagroup were more heterogeneous, in agreement with the four subclades known. Among the Tremellomycetidae, the members of theCystofilobasidiumandTremellaclades showed a reduced or null ability to utilize aromatic compounds. In contrast, the members of theTrichosporonclade were able to utilize phenol and similar substrates, and the representatives of theFilobasidiumclade assimilated various aromatic compounds, including those requiring more complex catabolic routes. Assimilation tests using, as sole carbon and energy sources, low molecular weight aromatic compounds appear to be potentially useful in taxonomic studies of basidiomycetous yeasts. In those species in which a considerable number of strains was investigated, variable assimilation patterns were frequently observed. The possibility that such discrepant results indicate an incorrect species delimitation is discussed.Key words: aromatic compounds, yeasts, heterobasidiomycetes, systematics.

ISSN:0008-4166    

DOI:10.1139/w99-020

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Using a semi-continuous enrichment method, we isolated two thermophilic bacterial strains, which could completely degrade abietane resin acids, including dehydroabietic acid (DhA). Strain DhA-73, isolated from a laboratory-scale bioreactor treating bleached kraft mill effluent at 55°C, grew on DhA as sole carbon source; while DhA-71, isolated from municipal compost, required dilute tryptic soy broth for growth on DhA. DhA-71 grew on DhA from 30°C to 60°C with maximum growth at 50°C; while, DhA-73 grew on DhA from 37°C to 60°C with maximum growth at 55°C. At 55°C, the doubling times for DhA-71 and DhA-73 were 3.3 and 3.7 h, respectively. DhA-71 and DhA-73 had growth yields of 0.26 and 0.19 g of protein per g of DhA, respectively. During growth on DhA, both strains converted DhA to CO2, biomass, and dissolved organic carbon. Analyses of the 16S-rDNA sequences of these two strains suggest that they belong to two new genera in theRubrivivaxsubgroup of the beta subclass of theProteobacteria. Strains DhA-71 and DhA-73 are the first two bacteria isolated and characterized that are capable of biodegradation of resin acids at high temperatures. This study provided direct evidence for biodegradation of resin acids and feasibility for biotreatment of pulp mill effluent at elevated temperatures.Key words: biodegradation, resin acid, semi-continuous enrichment, therm

ISSN:0008-4166    

DOI:10.1139/w99-028

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A polycyclic aromatic hydrocarbon (PAH)-degrading culture enriched from contaminated river sediments and aMycobacteriumsp. isolated from the enrichment were tested to investigate the possible synergistic and antagonistic interactions affecting the degradation of pyrene in the presence of low molecular weight PAHs. TheMycobacteriumsp. was able to mineralize 63% of the added pyrene when it was present as a sole source of carbon and energy. When the enrichment culture and the isolated bacterium were exposed to phenanthrene, de novo protein synthesis was not required for the rapid mineralization of pyrene, which reached 52% in chloramphenicol-treated cultures and 44% in the absence of the protein inhibitor. In the presence of chloramphenicol, <1% of the added pyrene was mineralized by the mixed culture after exposure to anthracene and naphthalene. These compounds did not inhibit pyrene utilization when present at the same time as pyrene. Concurrent mineralization of pyrene and phenanthrene after exposure to either compound was observed. Cross-acclimation between ring classes of PAHs may be a potentially important interaction influencing the biodegradation of aromatic compounds in contaminated environments.Key words: pyrene, polycyclic aromatic hydrocarbons (PAHs), biodegradation,Mycobacteriumsp.

ISSN:0008-4166    

DOI:10.1139/w99-018

出版商:NRC Research Press    

年代:1999

数据来源: NRC