摘要:

Bacillus subtilisandAgrobacterium radiobacterremained viable when exposed to Ni (1 × 10−4 M; ionic strength (μ) = 3 × 10−4) at pH values known to cause a change of the net negative charge of the cells to a net positive charge (charge reversal). The gross morphology, as determined by scanning electron microscopy, of these and other bacteria and ofSaccharomyces cerevisiaewas not altered in the presence of Ni, Cu, and Zn (1 × 10−4 M; μ = 3 × 10−4), which caused a charge reversal at pH values between 6.0 and 9.0. Similar results were obtained in the presence of Na and Mg, which did not cause charge reversal at the same μ and pH values. These results confirmed that cells remain viable when their surface charge is changed in the presence of some heavy metals at high pH values.Key words: heavy metals, electrokinetic properties, survival of bacteria.

ISSN:0008-4166    

DOI:10.1139/m96-085

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Clostridium perfringensproduced eight extracellular and two intracellular amylolytic activities when examined by zymograms following polyacrylamide gel electrophoresis under native conditions. The major intracellular amylase was isolated from vegetative cells ofC.perfringens. It possessed an estimated molecular mass of 112 kDa. Sulfhydryl and phenol functional groups were essential to its activity. The amylase wasendo-acting on starch and also hydrolyzed pullulan. Polyclonal antisera against a purified extracellular amylase did not cross-react with intracellular amylase and the two amylases were biochemically different. The distribution of extracellular amylolytic activities of sporulating cells was different from that of vegetative cells, whereas the distribution of intracellular amylolytic activities remained identical. A significant increase of a particular amylase (A8) occurred in the extracellular fluid during sporulation compared with that during vegetative growth. Regulation of the excretion of amylase(s) may be sporulation and enterotoxingenicity related.Key words:Clostridium perfringens, amylase, sporulation.

ISSN:0008-4166    

DOI:10.1139/m96-086

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Light microscopy was used to investigate the relation between toxicity, cytopathological effects, and in vivo binding ofBacillus thuringiensisCrylA(b) and CrylE toxin proteins in larvae ofLymantria dispar,Choristoneura fumiferana,Actebia fennica, andBombyx mori. These target insects were selected for their contrasting susceptibility to the two toxins.Lymantria disparis susceptible to CrylA(b),B.moriis susceptible to CrylE,C.fumiferanais susceptible to both, andA.fennicais not susceptible to either. In the susceptible species, both toxins caused typical pathological changes in midgut epithelial cells, including disruption and shedding of the brush border membrane, vacuolization of the cytoplasm, and swelling of the cells and their nuclei, followed by disintegration and release of cytoplasmic content into the lumen. In the highly resistantA.fennica, no cell damage was observed, but the midguts of toxin-fed larvae had a shrunken appearance. Immunohistochemical staining of midgut sections from toxin-fed larvae revealed that the toxins bound to the microvilli of the midgut epithelial cells of susceptible species only, with the exception ofB.mori. In this species, the CrylA(b) toxin bound to the apical microvilli without causing cell damage or larval death. In vivo binding of toxins is thus not always correlated with larval toxicity. Accumulation of the toxins at the peritrophic membrane depended on both toxin and insect species and was not correlated with larval toxicity.Key words:Bacillus thuringiensis, Cryl toxins, forest Lepidoptera, immunocytochemical localization, cytopathology.

ISSN:0008-4166    

DOI:10.1139/m96-087

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

We obtained an organic solvent-sensitive bacterium capable of degrading dibenzothiophene (DBT) under microaerobic (nitrogen exchange) conditions. The bacterium with the highest DBT-degradative activity was mutated and ann-heptanol-resistant mutant was selected. Although the parent strain did not grow in 0.1% v/vn-heptanol at all, the mutant did grow even in 50% heptanol and could still retain the ability to degrade and assimilate DBT in 5–10% heptanol, nonanol, or decanol under microaerobic conditions. The percentages of odd-chain fatty acids (C15and C17), unsaturated fatty acids (especially thetransform), and isooctadecanoic acid were significantly greater in the mutant strain than the parent strain.Key words: dibenzothiophene,n-heptanol tolerance,Pseudomonas putida, fatty acid.

ISSN:0008-4166    

DOI:10.1139/m96-088

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Epicoccum nigrumis a potential biological control agent for certain plant diseases, such as white mold of bean caused bySclerotinia sclerotiorum. To provide information that could be used to improve the production and efficacy ofE.nigrum, the effects of nutrients, including specific carbohydrate sources and amino acids, on mycelial growth, sporulation, germination of conidia, and elongation of germ tubes were determined. In dual cultures ofE.nigrumandS.sclerotiorum, the effects of nutrients on widths of inhibition zones between the two fungi were assessed. Standard mycological media supported faster radial growth than media with single carbohydrate sources and individual amino acids, but glutamic acid combined with maltose or dextrose was similar with respect to stimulation of sporulation when compared with media such as V8 juice and yeast extract agars. Dual culture inhibition zones were greater in certain simple media (dextrose and lysine, sucrose and lysine, and maltose and lysine) than in standard media. For germination and germ tube elongation, sucrose and maltose were superior to most other carbohydrate sources tested, and lysine and glutamic acid were superior amino acid sources. When standard broth media were compared for production of antifungal compounds byE.nigrum, both potato dextrose broth and malt extract broth were superior to Czapek solution. Culture filtrates ofE.nigrumgrown in potato dextrose broth were more inhibitory towardsS.sclerotiorumthan filtrates from malt extract cultures.Key words: biological control, white mold,Epicoccum purpurascens, antibiosis.

ISSN:0008-4166    

DOI:10.1139/m96-089

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The growth yield ofAzotobacter salinestris, a Na+-dependent, microaerophilic nitrogen-fixing bacterium, was inhibited more than 60% by 5 μM Zn2+. This organism was much more sensitive to Zn2+than the obligate aerobeAzotobacter vinelandii. Inhibition ofA.salinestriswas most evident in iron-limited cells and exogenously added Fe2+was more effective than Fe3+in preventing inhibition by Zn2+. While Zn2+decreased the Fe content of the cells, decreased the activity of the soluble cytoplasmic ferric reductase, and altered the intracellular Fe2+/Fe3+ratio, which in turn increased siderophore production, none of these effects appeared severe enough to account for growth inhibition. However, Zn2+also was observed to be a powerful inhibitor of Fe-limited whole cell respiration. As the cells became more Fe sufficient, this inhibition of respiration was decreased. Growth ofA.salinestrisalso was inhibited by Cd2+ > Zn2+ > Cu2+ > Cr2+ > Ni2+ > Co2+, and inhibition by these ions also was reversed by exogenous Fe2+or Fe3+. Examination of isolated cell membranes showed that the sensitivity ofA.salinestrisNADH oxidase activity to Zn2+and other respiratory poisons changed as the cells became Fe sufficient, but a similar change did not occur inA.vinelandii. It is proposed that Fe-limitedA.salinestriscells present a sensitive target for Zn2+inhibition, possibly a sulfhydryl group in a terminal oxidase, but this target is lost or is of decreased importance in Fe-sufficient cells.Key words: ferric reductase, iron uptake, respiratory poison, zinc, microaerophile.

ISSN:0008-4166    

DOI:10.1139/m96-090

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A chromosomally located operon (ars) ofEscherichia colihas been previously shown to be functional in arsenic detoxification. DNA sequencing revealed three open reading frames homologous to thearsR,arsB, andarsCopen reading frames of plasmid-based arsenic resistance operons isolated from bothE.coliand staphylococcal species. To examine the outline of transcriptional regulation of the chromosomalarsoperon, several transcriptional fusions, using the luciferase-encodingluxABgenes ofVibrio harveyi, were constructed. Measurement of the expression of these gene fusions demonstrated that the operon was rapidly induced by sodium arsenite and negatively regulated by thetrans-actingarsRgene product. Northern blotting and primer extension analyses revealed that the chromosomalarsoperon is most likely transcribed as a single mRNA of approximately 2100 nucleotides in length and processed into two smaller mRNA products in a manner similar to that found in theE.coliR773 plasmid-bornearsoperon. However, transcription was found to initiate at a position that is relatively further upstream of the initiation codon of thearsRcoding sequence than that determined for theE.coliR773 plasmid'sarsoperon.Key words: arsenic resistance,Escherichia coli, transcription, gene fusions.

ISSN:0008-4166    

DOI:10.1139/m96-091

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The paracrystalline surface layer (S-layer) ofCaulobacter crescentusis composed of a single protein (RsaA, 1026 amino acids) that associates noncovalently with the lipopolysaccharide of the outer membrane. Like many other extracellular proteins of Gram-negative bacteria, the S-layer protein is not processed during transport to the cell surface. To study the secretion of RsaA, several N-terminal deletions of the protein were made by modifying the 5′-region of thersaAgene. This analysis showed that portions of the N-terminus totalling the first 775 N-terminal amino acids (75% of the protein) could be removed from RsaA without abolishing secretion of the remainder of the protein. Although the RsaA N-terminus was not required for secretion, an N-terminal domain consisting of either 34 or 52 RsaA-derived amino acids promoted export of the alkaline phosphatase reporter (PhoA) and a cellulase reporter (ΔCenA) from the cytoplasm; using the cellulase reporter, the efficiency of hybrid protein export was estimated at 9%. No enzyme activity was detected in the cell-free culture fluids as the result of expressing any gene fusion, indicating that no hybrid protein was completely secreted from the cell. RsaA:PhoA hybrid proteins were also exported from theE.colicytoplasm, a bacterium not expected to contain the necessary machinery for the secretion of RsaA. Taken together, these data indicate that the secretion pathway of RsaA relies on a C-terminal secretion signal and that once separated from the context of the native protein, the extreme N-terminus of RsaA can act as an inefficient cryptic export signal that is not used during native RsaA secretion.Key words:Caulobacter, S-layer, protein secretion.

ISSN:0008-4166    

DOI:10.1139/m96-092

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Some small-spored species belonging to the genusAlternariaNees have been studied according to their chemical, morphological, and cultural characteristics. A data matrix was constructed based on a combination of characters. Cluster analysis of the combined data set showed good resolution of two groups of small-sporedAlternaria: theAlternaria infectoriagroup and theAlternaria alternatagroup. Isolates in theA.infectoriagroup produced only unique metabolites of unknown identity, whereas all isolates in theA.alternatagroup produced alternariol and alternariol monomethyl ether. Furthermore, the analysis showed that theA.alternatagroup andA.infectoriagroup each could be subdivided into three groups. The colour of fungal colonies on dichloran rose bengal yeast extract sucrose agar was another useful character to differentiate between theA.infectoriaand A.alternatagroups.Key words: Alternaria infectoria,Alternaria alternata, secondary metabolites, cluster analysis.

ISSN:0008-4166    

DOI:10.1139/m96-093

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A microbial culture collection composed of 1820 bacterial strains, including 298 actinomycete strains, was established from the roots of Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco) seedlings harvested from conifer nurseries and forest sites. Two hundred and thirty-four strains inhibited the growth ofFusarium,Cylindrocarpon, and (or)Pythiumspp. in in vitro assays. A significantly greater proportion of bacterial strains from actinomycete genera exhibited antifungal properties compared with bacterial strains from nonactinomycete genera. Eighty-nine percent of identified inhibitory strains wereStreptomyces,Streptoverticillium,Bacillus,Pseudomonas, orBurkholderiaspecies. The actinomycete species were isolated almost exclusively from forest seedlings. Recovery of inhibitory strains representing 29 microbial species was enhanced using a variety of methods to isolate microorganisms from the roots of seedlings from nursery and forest sites. Bacterial strains (including actinomycete strains) with antifungal activity were tested for in vitro growth inhibition of six clinical human bacterial pathogens (Enterococcus faecalis,Staphylococcus aureus,Klebsiella pneumoniae,Escherichia coli,Proteus mirabilis, andPseudomonas aeruginosa). Forty-eight percent of the tested strains inhibited one or more human pathogens. Inhibitory activity towards fungal and bacterial pathogens was strain specific, not species specific, and many inhibitory strains exhibited broad-spectrum activity. Strains with antifungal activity against several conifer root pathogens were also more likely to inhibit multiple species of clinical bacterial pathogens.Key words: in vitro, antimicrobial, conifer rhizosphere.

ISSN:0008-4166    

DOI:10.1139/m96-094

出版商:NRC Research Press    

年代:1996

数据来源: NRC