摘要:

Oxalobacterformigenesis the only well-documented oxalate-degrading bacterium isolated from the gastrointestinal tract of animals. The production of ATP byOxalobacter formigenesis centered around oxalate metabolism and oxalate is required for growth. A small amount of acetate (0.5 mM) is also required. Oxalate is decarboxylated to formate plus CO2in nearly equimolar amounts. Experiments were conducted to determine which potential carbon sources (oxalate, acetate, formate, CO2) were assimilated byOxalobacter formigenesand which metabolic pathways were operative in carbon assimilation. Measurements of the specific activities of total cell carbon after growth with different14C-labeled precursors indicated that at least 54% of the total cell carbon was derived from oxalate and at least 7% was derived from acetate. Carbonate was also assimilated, but formate was not a significant source of cell carbon. Labeling patterns in amino acids from cells grown in [14C]oxalate or14CO3were different; however, in both cases14C was widely distributed into most cellular amino acids. Carbon from [14C]acetate was less widely distributed and detected mainly in those amino acids known to be derived from α-ketoglutarate, oxaloacetate, and pyruvate. Cell-free extracts contained citrate synthase, isocitrate dehydrogenase, and malate dehydrogenase activities. The labeling observed in amino acids derived from acetate is in agreement with the function of these enzymes in biosynthesis and indicates that the majority of acetate carbon entered into amino acid biosynthesis via well-known pathways.Key words: biosynthesis, carbon assimilation, metabolism.

ISSN:0008-4166    

DOI:10.1139/m96-138

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The marine microalgaChlorella autotrophicawas cultured semicontinuously under light–dark synchronizing conditions at two nutrient concentrations (2 and 4 mmol N∙L−1) and five rates of daily renewal (from 10 to 50% of culture volume). Under such conditions, the biochemical composition ofC.autotrophicawas strongly influenced by the renewal rate, but unlike other marine microalgae, the nutrient concentration had no effect on the biochemical composition of the organic fraction of the microalga at a given growth rate. Results suggest that this species exerts a strong control over metabolic pathways, independent of the nutrient concentration in the medium.Key words:Chlorella autotrophica, semicontinuous culture, biochemical compositio

ISSN:0008-4166    

DOI:10.1139/m96-139

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Kinetics of [1-13C]glucose utilization were monitored by in vivo NMR spectroscopy on resting cells ofFibrobacter succinogenes, in the presence of 32 mM [1-13C]glucose, 32 mM [1-13C]glucose and 64 mM unlabelled glucose, or 32 mM [1-13C]glucose and 32 mM unlabelled cellobiose. A similar production of acetate and succinate and a similar storage of glycogen were observed whatever the exogenous substrate. The presence of cellobiose or that of an equivalent amount of glucose did not reduce [1-13C]glucose incorporation to the same extent. Glucose seemed preferentially used for glycogen storage and energy production, while part of the cellobiose appeared to be used for cellodextrin synthesis. Both cellobiase and cellobiose phosphorylase activities were assayed in cell-free extracts. Finally, the intracellular concentration of glucose 6-phosphate was increased by over threefold when cells metabolized cellobiose (alone or in parallel to glucose) as compared with the metabolism of glucose alone.Key words:Fibrobacter succinogenes, rumen, glucose 6-phosphate, cellobiose, NMR.

ISSN:0008-4166    

DOI:10.1139/m96-140

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Ochratoxin A, a known mycotoxin with demonstrated toxicity to insects, has been isolated from the sclerotia of the fungusAspergillus carbonariusNRRL 369. The sclerotia, harvested from a solid substrate fermentation of corn kernels at 28 °C, produced quantities of ochratoxin A exceeding 50 ppm/g dry weight of sclerotia. Evidence is presented that ochratoxin A accounts for the activity of the methanol extract against larvae of the detritivorous beetleCarpophilus hemipterus(Nitidulidae) (75% reduction in feeding rate) and corn ear wormHelicoverpa zea(50% mortality with 99% reduction in weight gain among surviving larvae) when incorporated into a pinto bean diet at levels less than those occurring naturally in the sclerotia.Key words: ochratoxin A,Aspergillus carbonarius, sclerotia,Helicoverpa zea,Carpophilus hemipterus, antiinsectan, chemical defense.

ISSN:0008-4166    

DOI:10.1139/m96-141

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Streptococcal pyrogenic exotoxin type C (SPE C) is a member of the bacterial superantigens that are potent stimulants of T cells. We expressed SPE C inEscherichia coliand characterized its selective stimulation properties on human T cells bearing specific Vβ chains of T-cell receptors (TCRs). Cytokine profiles induced by SPE C were also examined. Recombinant SPE C significantly enhanced proliferation of human peripheral blood mononuclear cells (PBMCs) at concentrations as low as 10−12–10−14 M. Reverse transcription of RNA from SPE-C-stimulated PBMCs followed by polymerase chain reaction, revealed selective induction of TCR Vβ2 chain expression. SPE C raised the mRNA level of type 1 helper T cell (TH1) related cytokines, such as interferon γ (IFN-γ), interleukin 2 (IL-2), and tumor necrosis factor β (TNFβ). The expression of TNFα was also increased. In contrast, the increase in mRNA levels of the p35 small fragment of IL-12 and type 2 helper T cell (TH2) related cytokines (i.e., IL-4 and IL-10) was not significantly affected by SPE C. The mRNA level of proinflammatory cytokine IL-6 was increased marginally. Consistent with the mRNA accumulation, protein concentrations of IFNγ, IL-2, and TNF were increased in SPE-C-stimulated PBMCs, but IL-4 was not. From these results, we conclude that the stimuli of SPE C preferentially causes the TH1 responses in human T cells bearing TCR Vβ2.Key words: streptococcal pyrogenic exotoxin C,Streptococcus pyogenes, T cells, cytokine, superantigen.

ISSN:0008-4166    

DOI:10.1139/m96-142

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Following inoculation onto seeds, the rhizobacteriumPseudomonas aureofaciensPs3732RNL11 (L11), which contains the constituitively expressedlacZandlacYgenes fromEscherichia coli, was recovered from the interior of aerial tissues of all 16 monocot and dicot plants tested, and the exterior of aerial surfaces of 15. In more detailed studies with corn, wheat, and broccoli, both Ps3732RNL11 and its nonengineered parent strain PS3732RN (RN) rapidly established large populations on all root systems and smaller densities within the aerial tissues, all of which persisted at stable levels throughout 12- to 23-day test periods. There were no differences in the behavior of L11 and RN on any of the three plant species. L11 invaded the aeriel tissues of corn in at least two distinct ways. First, it moved into the interior of leaves following inoculation of guttation drops, suggesting that the bacteria may contaminate the developing shoot prior to its emergence from the soil and then invade through natural openings. However, when this route was blocked by inoculating the roots after shoot emergence in either soil or hydroponic systems, the bacteria still invaded the aerial tissues within 24 h, suggesting direct vascular transport from the roots. Such bacterial movement is an important consideration in future field releases of both native and genetically modified rhizobacteria.Key words: rhizosphere, genetically engineered microorganism,Pseudomonas aureofaciens.

ISSN:0008-4166    

DOI:10.1139/m96-143

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Symbiotic gene diversity and other measures of genetic diversity were examined inBradyrhizobiumisolates that form an effective symbiosis with peanut (Arachis hypogaea). Initially, restriction fragment length polymorphism (RFLP) analysis using a nitrogenase (nif) gene probe was performed on 33 isolates along with oneBradyrhizobium elkaniiand twoBradyrhizobium japonicumstrains. Considerable diversity was observed among the RFLP patterns of many of the isolates, especially those from South America. Some isolates, however, were found to have similarnifand subsequentnod(nodulation) gene RFLP patterns, indicating symbiotic gene relatedness. With some noted exceptions, symbiotic gene relatedness correlated with relatedness based on total DNA homology and ribotyping analyses. Symbiotic gene relatedness also correlated with symbiotic effectiveness. The RFLP and DNA homology analyses indicate that bradyrhizobia effective with peanut are genetically diverse and consist of at least three different species. This diversity, however, was not particularly evident with partial 16S rRNA gene sequencing. Sequences obtained from the isolates were very similar to each other as well as to sequences previously reported for otherBradyrhizobiumstrains.Key words:Bradyrhizobium,nif, peanut, restriction fragment length polymorphism, 16S rRNA.

ISSN:0008-4166    

DOI:10.1139/m96-144

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Stems of susceptible and resistant cassava plants have been cytologically investigated for their defense reactions to an aggressive strain ofXanthomonas campestrispv.manihotis. Histochemistry, in conjunction with gold cytochemistry, revealed that in susceptible and resistant plants, phloem and xylem parenchyma cells displayed a wide range of responses that limited the bacterial growth within the infected plants. Lignification and suberization associated with callose deposition were effective mechanisms that reinforced host barriers in the phloem. In the infected xylem, vessels were plugged by a material of pectic and (or) lignin-like origin. Flavonoids have been seen to be incorporated in secondary cell wall coatings. These reactions occurred at a higher intensity in the resistant plants. The number of phoem and xylem cells producing autofluorescent compounds was higher in infected resistant plants than in susceptible plants. Reactions have been observed in the resistant variety only, such as secretion of phenol-like molecules by tyloses and hyperplasic activity of phloem cells that compartmentalized bacterial lysis pockets, which are potent secondary inoculum sources.Key words: lignin, suberin, callose, phenol, tylose, flavonoid, pectin.

ISSN:0008-4166    

DOI:10.1139/m96-145

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Immunological methods were used to study the colonization of internal tissues of different plant species by the endophytic bacteriumEnterobacter asburiaeJM22. Polyclonal and monoclonal antibodies applied in enzyme-linked immunosorbent assay (ELISA), dot blot assay, tissue printing, or immunogold labeling were sensitive and specific enough to detect JM22 in plant tissues. Detection limits were 1.0 × 103colony-forming units (CFUs)/mL for tissue printing, 1.0 × 104 CFUs/mL for ELISA and 1.0 × 105 CFUs/mL for dot blot assay. Polyclonal and monoclonal antibodies showed a positive immunological reaction with nearly all testedEnterobacterspp. In contrast with polyclonal antibodies, the monoclonal antibodies differentiatedEnterobacterspp. and closely related genera likePantoeaorSerratia. Other bacterial genera, plant sap from nontreated field-grown crops, and soil solutions did not react with the antisera. When applied as a seed treatment, JM22 colonized roots, stems, and cotyledons of bean, cucumber, and cotton plants. Fourteen days after inoculation of cotton cotyledons or leaves, JM22 was detected inside the inoculated plant tissue and the bacteria moved to the roots. JM22 reached concentrations up to 1.0 × 105 CFUs/g in roots, 1.0 × 104 CFUs/g in stems, and 1.0 × 103 CFUs/g in cotyledons or leaves. Population densities of JM22 varied between the different plant species, being highest in bean and lowest in cotton. JM22 was detected with ELISA in different plant growth media. While sand, ground clay, and loamy sand showed high and comparable ELISA readings, the extinctions of sandy loam and Promix were significantly lower than the ones of the other three growth media, indicating a strong influence of soil mixes on immunological reactions. JM22 showed an intensive gold label in drop preparations of bacterial suspensions in phosphate buffer, plant sap, and ultrathin sections of plant tissue. After seed treatment, the bacteria were located on the root surface, concentrated in grooves between epidermal cells, below collapsed epidermal cells, within epidermal cells, and inside intercellular spaces in the root cortex close to conducting elements. Inoculation of leaves or cotyledons resulted in the occurrence of many gold labeled cells of JM22 on the petiole surfaces.Enterobacter asburiaecolonizes different plant species and establishes endophytic populations in various tissues.Key words: immunology, endophytic bacteria, colonization, localization, plant species.

ISSN:0008-4166    

DOI:10.1139/m96-146

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

In this study, the 16S/23S rRNA intergenic spacer (IGS) regions of sixListeriaspecies were examined. DNA bands of 590 and 340 bp were observed following polymerase chain reaction (PCR) amplification of DNA fromListeria monocytogenes,Listeria innocua,Listeria seeligeri,Listeria welshimeri, andListeria ivanoviistrains with generic rRNA IGS oligonucleotide primers. For strains ofListeria grayisubspp.grayiandmurrayi, DNA band sizes of 550 and 340 bp were observed with this primer pair. DNA bands of these sizes were not observed for other Gram-negative or -positive bacteria in this PCR assay. FourRsaI digestion profiles were noted for theListeriaPCR products.Listeria monocytogenesstrains had one profile;L.innocuastrains had a second;L.seeligeri,L.welshimeri, andL.ivanoviistrains had a third; andL.grayistrains had a fourth. The small and large 16S/23S rRNA IGSs ofL.monocytogenesATCC 15313 were identical in the first 58 5′ and the last 169 3′ nucleotides. However, the large rRNA IGS contained a central 267-bp region with tRNAIleand tRNAAlagenes. Large rRNA 16S/23S IGS nucleotide sequence data has not been previously reported. This data was used to develop novelListeriagenus-specific andL.monocytogenesspecies-specific PCR assays.Key words: polymerase chain reaction, 16S/23S rRNA intergenic spacer region,Listeria monocytogenes.

ISSN:0008-4166    

DOI:10.1139/m96-147

出版商:NRC Research Press    

年代:1996

数据来源: NRC