摘要:

Oxalate secretion by fungi provides many advantages for their growth and colonization of substrates. The role of oxalic acid in pathogenesis is through acidification of host tissues and sequestration of calcium from host cell walls. The formation of calcium oxalate crystals weakens the cell walls, thereby allowing polygalacturonase to effect degradation more rapidly in a synergistic response. There is good correlation between pathogenesis, virulence, and oxalic acid secretion. Solubility of soil nutrients is achieved by soil-living species, when cations freed by oxalate diffusing in clay layers increases the effective solubility of Al and Fe. Oxalate retained in hyphal mats of mycorrhizal species increases phosphate and sulphate availability. The formation of calcium oxalate crystals provides a reservoir of calcium in the ecosystem. The ability of oxalate to bind divalent cations permits detoxification of copper, particularly evident in wood preserved with copper salts. Oxalate plays a unique role in lignocellulose degradation by wood-rotting basidiomycetes, acting as a low molecular mass agent initiating decay. In addition, in white-rot fungi oxalate acts as a potential electron donor for lignin-peroxidase catalysed reduction and chelates manganese, allowing the dissolution of Mn3+from the manganese–enzyme complex and thus stimulating extracellular manganese peroxidase activity. The biosynthesis and degradation of oxalate are discussed.Key words: oxalic acid, calcium oxalate, pathogenicity, fungi.

ISSN:0008-4166    

DOI:10.1139/m96-114

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Lysobacter enzymogenesandLysobacter brunescensare Gram-negative gliding bacteria that belong to the γ subgroup of the proteobacteria. As a first step toward a molecular analysis ofLysobactergliding motility, we developed techniques to genetically manipulate these bacteria. Cosmid pSUP106 of the broad host range incompatibility group Q (Inc Q) was introduced intoL.enzymogenes and L.brunescensby conjugation and electroporation. pSUP106 replicated stably in both organisms and conferred antibiotic resistance. We also identified several other plasmids (pKT210, pH1JI) that functioned inL.enzymogenesand a transposon (mini-Tn5Sp) that functioned inL.brunescens. The identification of these tools allows genetic analysis ofLysobactergliding motility, exoenzyme production, and production of antibiotics and other secondary metabolites.Key words:Lysobacter, gliding motility, gene transfer.

ISSN:0008-4166    

DOI:10.1139/m96-115

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Rhizobium etliTAL182, a competitive strain for the nodulation ofPhaseolusbeans, occupied more than 99% of the nodules when co-inoculated in various proportions withRhizobiumTAL1145 orRhizobium tropiciCIAT899. Two overlapping cosmid clones, pUHR68 and pUHR69, containing genes for nodulation competitiveness from TAL182, were isolated by functional complementation of strain TAL1145. Using one of these cosmid clones, we constructed two Tn5-insertion mutants of TAL182 defective in nodulation competitiveness. The Tn5insertions in both mutants were localized in identical positions within a 4.6-kbHindIII fragment. One mutant, RUH120, was complemented for nodulation competitiveness by thisHindIII fragment. The cloned DNA in pUHR68 is a part of a plasmid, 150 MDa in size, in TAL182 and does not show homology with TAL1145 genomic DNA. The 4.6-kbHindIII fragment contains a gene(s) required for nodulation competitiveness on beans, which is present only in someR.etlistrains and absent in otherRhizobiumspp.Key words: nitrogen fixation, competition, nodule, common bean.

ISSN:0008-4166    

DOI:10.1139/m96-116

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The effects of sorptive inert surfaces on growth of marine bacteria and metabolism, as well as partitioning of organic substrates, were examined in microcosms inoculated with bacterioplankton from a local salt marsh. Introduction of organic-free glass beads to a dilute seawater medium (tryptic soy broth) increased yields of ATP, a surrogate for bacterial biomass, by 187% within the entire microcosm (attached + free-living). Growth efficiencies (bacterial C/media C) were 30% for bacteria grown in microcosms with beads compared with 16% without beads. Surface enrichment increased rates of proteolytic enzyme activity and cell-specific [3H]leucine incorporation into protein by factors of 6.8 and 2.2, respectively. Scanning electron microscopy revealed obvious organic coatings on all beads after 2 h of exposure, but few strongly attached bacteria were evident, even after 40 h of exposure. Results support the hypothesis that mineral surfaces facilitate bacterial utilization of complex organic matter through physical–chemical processes that increase conversion efficiencies of labile substrate despite possible kinetic limitations. Furthermore, firm attachment by bacteria to these surfaces is apparently not a requirement to produce surface-enhanced activity.Key words: epibacteria, sorption, interfaces, hydrolytic enzymes, growth efficiency.

ISSN:0008-4166    

DOI:10.1139/m96-117

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Phage 2C is aBacillus subtilislytic phage, whose genome contains hydroxymethyluracil in place of thymine. To isolate promoters of early phage genes involved in the take-over of cellular metabolism, 2C DNA libraries were constructed in promoter-probe plasmids replicating inEscherichia coliandB.subtilis. Four different 2C DNA fragments strongly expressed reporter genes inE.colibut not inB.subtilis. All fragments originated from unique sequences of the genome and not from its terminal redundancies. One fragment was sequenced. Despite the presence of an σA-RNA polymerase binding site upstream of the transcriptional initiation site of a 2C early gene, this fragment did not promote transcription inB.subtilis.Key words: hydroxymethyluracil, lytic phage, promoter-probe plasmid,Bacillus subtilis, gene expression.

ISSN:0008-4166    

DOI:10.1139/m96-118

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The effect of Levucell® SC, a strain ofSaccharomyces cerevisiaemarked as a feed additive for ruminants, was investigated in vitro on lactate metabolism by the ruminal bacteriaStreptococcus bovisandMegasphaera elsdenii. The coculture between 107live cells∙mL−1of SC and aStreptococcus bovisstrain in the presence of glucose reduced lactate production by the bacterial strain. Live yeast cells were able to compete withStreptococcus bovisfor glucose utilization in strictly anaerobic conditions, so less glucose was available for the bacterium. SC also stimulatedL-lactate utilization by a strain ofM.elsdenii. The effect depended on the concentration of yeast cells added. Bacterial growth and fermentation end-product concentrations were also increased in the presence of SC. Some amino acids and vitamins, but not dicarboxylic acids, stimulated the bacterial specific activity ofL-lactate uptake. SC was able to provide amino acids toM.elsdenii. In a coculture ofStreptococcus bovisandM.elsdeniion glucose, the reduction of lactate concentration was improved by SC, the same trend being observed when maltose or soluble starch were used as carbon and energy source. These results indicate that SC can be a very useful tool to reduce lactate accumulation in vitro during fermentation of soluble sugars.Key words: rumen,Saccharomyces cerevisiae, lactate metabolism,Streptococcus bovis,Megasphaera elsdeni

ISSN:0008-4166    

DOI:10.1139/m96-119

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A 3.6-kb fragment of theFibrobacter succinogenesS85 DNA was sequenced and found to contain two open reading frames (ORFs) on the same strand separated by 242 nucleotide bases. The translated protein from ORF1 had a predicted mass of 52.3 kDa. In a region of 320 amino acid overlap, it shares a 35% identity with the b-chain of the glutamate synthase ofEscherichia coli. The ORF2 protein encodes a 519 residue protein designated CelG. It consists of an ORF of 1557 bp, encoding a polypeptide of 54.5 kDa. The N-terminal region, which contains the catalytic domain, is linked to a C-terminal basic domain, which has a predicted isoelectric point of 10.8. The catalytic domain in endoglucanase G (CelG) is homologous to the family 5 (A) cellulases. The enzyme has an apparent mass of 55 kDa, a pH optimum of 5.5, and temperature optimum of 25 °C. It had a specific activity of 16.5 mmol∙min−1∙mg−1on barley b-glucan and produced a mixture of cellooligosaccharides from the hydrolysis of acid swollen cellulose and cellooligosaccharides. Antiserum raised against the purified form of CelG inE.colifailed to react with proteins from the native organism when grown on either glucose or crystalline cellulose, but reverse transcription and polymerase chain reaction techniques using RNA from the native organism demonstrated that thecelGgene was expressed constitutively. Its distribution amongst subspecies ofFibrobacterwas restricted toF.succinogenesS85.Key words: basic terminal domain,Fibrobacter succinogenes, endoglucanase, nucleotide seque

ISSN:0008-4166    

DOI:10.1139/m96-120

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A glucantime sensitiveLeishmania(V.)guyanensisstrain was used to obtain in vitro resistant cell lines, by increments in glucantime concentrations employing both one step and stepwise protocols. Whereas the effective concentration of drug that inhibited the growth of wild type cells by 50% (EC50value) was 0.20 mg Sbv/mL, the resistant cells were able to grow in glucantime concentrations greater than 8.0 mg/mL. The resistant cell lines were partially characterized by their in vitro response to glucantime, the stability of resistance phenotype, cross resistance to a range of drugs, and also by the analysis of total DNA fragments generated by restriction endonucleases and blot hybridization. Amplified DNA sequence similar to a P-glycoprotein analog fromLeishmania tarentolae(ltpgpAgene) was observed in all the resistant cell lines obtained through the one-step protocol. These cell lines showed cross resistance to heavy metals but were sensitive to puromycin, vinblastine, and pentostam.Key words:Leishmania, glucantime resistance, pentavalent antimony, gene amplification.

ISSN:0008-4166    

DOI:10.1139/m96-121

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The molecular nature of a number ofcreAmutant alleles has been determined. Three alleles analysed are missense mutations in the DNA binding domain and predicted to reduce but not abolish binding. Of the other four alleles, two result from frameshifts: one has a nonsense mutation and the other has an inversion. All four alleles result in truncations of the protein after the zinc finger domain, such that the protein no longer contains at least the carboxy terminal 145 amino acids, so identifying a region required for repression. Transcriptional analysis ofcreAindicates that the transcript is autoregulated and analysis using 5′ rapid amplification of cDNA ends indicates that transcriptional start points exist in clusters over a region of 200 bp located up to 595 bp 5′ of the translational start point. The two major clusters have potential CREA-binding sites (SYGGRG) at appropriate positions to allow autoregulation. Autoregulation leads to thecreAtranscript being most abundant in carbon catabolite nonrepressing conditions, and this, together with the phenotypes of the mutant alleles, has led to the suggestion that CREA has effects under conditions generally not considered as carbon catabolite repressing, as well as in carbon catabolite repressing conditions.Key words: carbon catabolite repression, MIG1, CREA, zinc finger protein, transcriptional repressor.

ISSN:0008-4166    

DOI:10.1139/m96-122

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The effects of inoculum size, medium, temperature, and duration of growth on the in vitro susceptibility testing ofAspergillus fumigatuswere investigated using broth micro- and macro-dilution techniques. The minimum inhibitory concentrations (MICs) of ketoconazole, miconazole, itraconazole, fluconazole, and amphotericin B were significantly influenced by the inoculum size, regardless of the techniques used. Two- to four-fold higher MIC values were obtained when the inoculum size was increased 100-fold. The use of peptone yeast extract glucose and RPMI 1640 media provided essentially identical MIC values at 30 and 35 °C after incubation for 48 h or longer. A comparison of broth micro- and macro-dilution techniques revealed that, under equivalent conditions, the latter with an inoculum size between 1 × 103and 1 × 104conidia (strain W73355)/mL consistently provided the lowest MICs of fluconazole (256 μg/mL), ketoconazole (8 μg/mL), miconazole (2 μg/mL), itraconazole (0.25 μg/mL), and amphotericin B (0.25 μg/mL). Using the broth macrodilution technique, we screened 24 clinical isolates ofA.fumigatusobtained from the Detroit Medical Center in 1994. The MIC values of fluconazole, ketoconazole, miconazole, itraconazole and amphotericin B for all the isolates were 128–256, 8–16, 1–2, 0.25–0.5, and 0.25–1.0 μg/mL, respectively, indicating that none of the clinical isolates that we tested shows acquired resistance to the antifungals used.Key words:Aspergillus fumigatus, susceptibility test, antifungals, drug resistance, broth macrodilution.

ISSN:0008-4166    

DOI:10.1139/m96-123

出版商:NRC Research Press    

年代:1996

数据来源: NRC