Showing papers by "Ghent University published in 1994"
01 Jan 1994
TL;DR: The preservative effect of lactic acid bacteria during the manufacture and subsequent storage of fermented foods is mainly due to the acidic conditions that they create in the food during their development.
Abstract: The preservative effect of lactic acid bacteria during the manufacture and subsequent storage of fermented foods is mainly due to the acidic conditions that they create in the food during their development. This souring effect is primarily due to the fermentative conversion of carbohydrates to organic acids (lactic and acetic acid) with a concomitant lowering of the pH of the food, an important characteristic that leads to an increased shelf-life and safety of the final product. In recent decades, it has become clear that the overall inhibitory action of lactic acid bacteria is due to more complex antagonistic systems produced by the starter cultures. Lactic acid bacteria are capable of producing and excreting inhibitory substances other than lactic and acetic acid. These substances are antagonistic to a wide spectrum of microorganisms, and thus can make significant contributions to their preservative action. They are produced in much smaller amounts than lactic acid and acetic acid, and include formic acid, free fatty acids, ammonia, ethanol, hydrogen peroxide, diacetyl, acetoin, 2,3-butanediol, acetaldehyde, benzoate, bacteriolytic enzymes, bacteriocins and antibiotics, as well as several less well-defined or completely unidentified inhibitory substances (Klaenhammer, 1988; Daeschel, 1989; Lind-gren & Dobrogosz, 1990; Schillinger, 1990; Piard & Desmazeaud, 1991, 1992; Vandenbergh, 1993). Some of these substances display antagonistic activity towards many food spoilage and foodborne pathogenic microorganisms, including psychrotrophic lactobacilli and leuconostocs, Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Listeria monocytogenes, Staphyloc-occus aureus, etc. The competitive removal of essential substrates, the accumulation of D-amino acids, a lowering of oxidation-reduction potential and coaggregation may further restrict undesirable microorganisms. Unfortunately, in some instances the antibiosis will be detrimental by inhibition of other desirable lactic strains composing the mixed starter culture.
340 citations
TL;DR: A reporter gene-silencing event in Nicotiana tabacum is document that has a distinctive combination of features--i.e., silencing occurs by a posttranscriptional process, silencing correlates with DNA methylation, and this de novo methylation is not restricted to cytosines located in the symmetrical motifs CG and CXG.
Abstract: Endogenous plant genes or transgenes can be silenced on introduction of homologous gene sequences. Here we document a reporter gene-silencing event in Nicotiana tabacum that has a distinctive combination of features--i.e., (i) silencing occurs by a posttranscriptional process, (ii) silencing correlates with DNA methylation, and (iii) this de novo methylation is not restricted to cytosines located in the symmetrical motifs CG and CXG.
288 citations
TL;DR: FP images provide diagnostically useful information by depicting tissue vascularization and perfusion rather than benignity or malignancy, because there is an overlap in the slope values of highly vascular benign lesions and malignant lesions.
Abstract: PURPOSE: To assess the diagnostic value of parametric magnetic resonance images that display the first pass (FP) of gadopentetate dimeglumine. MATERIALS AND METHODS: Dynamic, contrast material-enhanced, fast low-angle shot MR imaging was performed of 100 musculoskeletal lesions in 36 female and 64 male patients (aged 9-81 years [mean, 34 years]). The highest slope value of the time-intensity curve was calculated pixel by pixel and displayed on the FP image, with a gray-scale value equal to the slope value. Tissue vascularization and perfusion were evaluated at pathologic and angiographic examinations in 33 lesions. RESULTS: A significant difference (P < .001) was found between the FP slope values of benign (mean, 36.2% per second) and malignant (mean, 67.4% per second) lesions. FP images depicted tissue vascularization and perfusion rather than benignity or malignancy, because there is an overlap in the slope values of highly vascular benign lesions and malignant lesions. CONCLUSION: FP images provide dia...
286 citations
TL;DR: The results suggest that Cyc1At accumulation in Arabidopsis is transcriptionally regulated and might be one of the limiting factors for the activation of cell division.
Abstract: In eukaryotes, the control of cell cycle progression is exercised by heteromeric protein kinase complexes composed of a cell cycle-dependent, kinase-related subunit (Cdc2) and a cyclin subunit. To explore the possibility that cyclin transcription plays a role in the developmental regulation of cell division, we examined the spatial and temporal expression of a cyclin gene (cyc1At) in Arabidopsis. In root and shoot apical meristems and during embryogenesis, cyc1At expression is almost exclusively confined to dividing cells. A cell-specific pattern of cyc1At expression was noticed in root meristems. We examined the effects of induction of cell division of differentiated cells on cyc1At expression. During lateral root formation, induction of cyc1At expression is a very early event and was detected before anatomical modifications were visible. Treatment of roots with oryzalin, which blocks cell division in metaphase, did not inhibit the auxin induction of cyc1At, suggesting that induction of cyc1At expression precedes the completion of the first division cycle after induction of lateral roots. In tobacco protoplasts, an increase in cyc1At expression was observed only when cell division was induced. Together, the results suggest that Cyc1At accumulation in Arabidopsis is transcriptionally regulated and might be one of the limiting factors for the activation of cell division.
264 citations
TL;DR: Results obtained using filter paper pretreated with one component, followed by inactivation and subsequent hydrolysis with the same or another cellulase component, point to a sequential enzymic attack of the cellulose and seems consistent with the mathematical model presented.
Abstract: The hydrolysis of Whatman no. 1 filter paper by purified cellulolytic components from Trichoderma reesei and the synergistic action of binary combinations of these enzymes on the same substrate were investigated. At 20 milligrams filter paper, enzyme concentrations needed to obtain half-maximal hydrolysis rates (KE values) were in the 3-4 microM range for the cellobiohydrolases (CBHs) and 0.05-0.10 microM for the endoglucanases (EGs). Catalytic-core proteins of CBH I and EG III, lacking the cellulose-binding domain, exhibit KE values 2.3 and 5.1 times higher than those of the intact enzymes. In synergistic combinations of two cellulases, the KE value of at least one enzyme was 3-10-fold reduced. CBH I/CBH II and CBH I/EG III combinations showed the most powerful synergism, and optimal ratios were a function of the total protein concentration. Results obtained in activity and adsorption assays using filter paper pretreated with one component, followed by inactivation and subsequent hydrolysis with the same or another cellulase component, point to a sequential enzymic attack of the cellulose and seems consistent with the mathematical model presented.
251 citations
TL;DR: Enhanced SOD activity in the mitochondria had only a minor effect on ozone tolerance, however, overproduction of SOD in the chloroplasts resulted in a 3–4 fold reduction of visible ozone injury.
Abstract: To evaluate the feasibility of using engineered antioxidant enzymes as an approach to improve the tolerance of plants to ambient stress, we have constructed transgenlc tobacco plants that overproduce superoxide dismutase (SOD), an enzyme which converts superoxide radicals into hydrogen peroxide and oxygen, and is believed to play a crucial role in antioxidant defense. We have targeted the MnSOD from Nicotiana plumbaginifolia either to the chloroplasts or to the mitochondria, and evaluated the ozone tolerance of transgenic and control plants. Enhanced SOD activity in the mitochondria had only a minor effect on ozone tolerance. However, overproduction of SOD in the chloroplasts resulted in a 3–4 fold reduction of visible ozone injury.
242 citations
TL;DR: The results obtained by the various validation experiments indicate that the SHIME reactor can be used to study the microbial communities of the gastrointestinal tract.
Abstract: The recently developed SHIME reactor (Simulator of the Human Intestinal Microbial Ecosystem) was validated by analysing a number of microorganism-associated activities. Data from the reactor were compared with values from the literature and results obtained from the analysis of faecal material of eight healthy persons. The fermentation patterns of four polysaccharides were studied. Arabinogalactan, xylan and pectin gave fermentation patterns in vitro indistinguishable from in vivo . Five different enzymatic activities were compared with in vivo experiments. All had activities which were of the order of those observed in vitro. The pro-drug sulphasalazine, whose active compound is released through microbial modification in the large intestine, was used as a reference compound. A fair correlation between in vivo and in vitro was found for the latter transformation. In addition the effect of Lactobacillus plantarum on the autochthonous microbial populations was investigated. Administration of L. plantarum resulted in an in vitro decrease in gram-negative anaerobic bacteria and total anaerobes. The same effect has been reported in vivo . The results obtained by the various validation experiments indicate that the reactor can be used to study the microbial communities of the gastrointestinal tract. Keywords - Gastrointestinal microbiology, In vitro simulation.
227 citations
TL;DR: The results of DNA-rRNA hybridization studies indicated that these two species belong to a separate genus in the alpha subclass (rRNA superfamily IV) of the Proteobacteria, for which the name Brevundimonas is proposed.
Abstract: The taxonomic positions of strains previously assigned to Pseudomonas diminuta and Pseudomonas vesicularis were investigated by a polyphasic approach. The results of DNA-rRNA hybridization studies indicated that these two species belong to a separate genus in the α subclass (rRNA superfamily IV) of the Proteobacteria, for which the name Brevundimonas is proposed. Genus delineation and species delineation were determined by comparing the results of numerical analyses of whole-cell protein patterns, fatty acid compositions, and phenotypic characteristics and by measuring DNA base ratios and degrees of DNA relatedness. Taxonomic characteristics of Brevundimonas diminuta and Brevundimonas vesicularis strains were compared with characteristics of reference strains belonging to the following phylogenetically related taxa: a group of organisms gathered in Enevold Falsen group 21, the genera Sphingomonas and Rhizomonas, and the generically misclassified organisms [Pseudomonas] echinoides and “[Pseudomonas] riboflavina.”
227 citations
01 Jan 1994
TL;DR: This chapter attempts to cover all aspects of nisin, with the main emphasis on its properties, biosynthesis and fermentative production, and on its applications.
Abstract: Nisin, which has been known for about five decades, is a lanthionine-containing bacteriocin produced by certain Lactococcus lactis subsp. lactis strains. A number of reviews have been published dealing with various aspects of nisin (Berridge, 1953; Hawley, 1957; Schaller, 1960; Hawley, 1962; Marth, 1966; Jarvis & Morisetti, 1969; Polanowski, 1972; Baranova & Egorov, 1973; Lipinska, 1977; Hurst, 1978, 1981, 1983; Rayman & Hurst, 1984; Bucci et al., 1990; Fowler & Gasson, 1991). This chapter attempts to cover all aspects of nisin, with the main emphasis on its properties, biosynthesis and fermentative production, and on its applications. However, the large number of publications on nisin precludes complete coverage of the literature; omissions or partial coverage of literature data should therefore not be considered as a slight to the authors. The genetics of nisin will be discussed in Chapter 6.
206 citations
TL;DR: Transgenic plants with suppressed SAM-S activity had a characteristic smell, a consequence of the accumulation of L-methionine that is converted into the volatile methanethiol, and a hypothesis is presented for this developmental gene silencing.
Abstract: S-Adenosyl-L-methionine synthetase (SAM-S) catalyzes the conversion of L-methionine and ATP into S-adenosyl-L-methionine. Tobacco plants that were transformed with a construct allowing high transcription levels of an Arabidopsis sam-s gene could be grouped into two main classes based on their morphology. One class developed yellow-green leaves and had high SAM-S activity and transgene mRNA levels, whereas the other class was stunted and had leather-like leaves, very low SAM-S activity, and suppressed mRNA level of the transgene. Because both overexpression and silencing of transgene expression led to distinct, abnormal phenotypes, the developmental pattern of transgene silencing was visualized. In the lower leaves, the suppressed phenotype was associated with the veins. In successive leaves, the area of the suppressed tissue increased until all newly developed leaves displayed the suppressed phenotype. In this study, a hypothesis is presented for this developmental gene silencing. Furthermore, transgenic plants with suppressed SAM-S activity had a characteristic smell, a consequence of the accumulation of L-methionine that is converted into the volatile methanethiol.
197 citations
TL;DR: The cloned wild‐type PFL gene is cloned by T‐DNA tagging, and it is demonstrated that it complements the mutant phenotype, and postulate that in meristematic tissues plants use transcriptional control to synthesize extra ribosomes to increase translational efficiency.
Abstract: In Arabidopsis, mutation at PFL causes pointed first leaves, reduced fresh weight and growth retardation. We have cloned the wild-type PFL gene by T-DNA tagging, and demonstrate that it complements the mutant phenotype. PFL codes for ribosomal protein S18, based on the high homology with rat S18 and on purification of S18-equivalent peptides from plant ribosomes. pfl represents the first mutation in eukaryotic S18 proteins or their S13 prokaryotic counterparts, involved in translation initiation. Arabidopsis contains three S18 gene copies dispersed in the genetic map; they are all transcribed and code for completely identical proteins. No transcript is detected from the mutated gene, S18A. The activity of the S18A promoter is restricted to meristems, with a markedly high expression at the embryonic heart stage, and to wounding sites. This means that plants activate an extra copy of this ribosomal protein gene in tissues with cell division activity. We postulate that in meristematic tissues plants use transcriptional control to synthesize extra ribosomes to increase translational efficiency. In analogy with this, an additional, developmentally regulated gene copy might be expected for all ribosomal proteins.
TL;DR: Tebufenozide induced a premature and lethal larval moult in larval Lepidoptera within 24 h of treatment and had a chemosterilizing activity in S. exigua, resulting in a total inhibition of oviposition within two days of continuous treatment at doses of ⩾ 10 mg litre−1.
Abstract: The nonsteroidal ecdysteroid agonist tebufenozide (RH-5992) was tested on larval stages of a number of lepidopteran species by topical application and by feeding on treated leaves. LC50, values in the range 0.03–0.10 mg litre−1 were obtained for third to sixth instars of Spodoptera exempta (Walker) when insects were fed on leaves dipped in aqueous emulsions of the compound, while first to fifth instars of Spodoptera exigua (Hubner) were less susceptible (LC50 values in the range 2.5–10.5 mg litre−1). When insects were topically treated, susceptibility of last-instar larvae of Lepidoptera tested decreased in the order Spodoptera exempta, Mamestra brassicae L., Spodoptera littoralis (Boisd.) S. exigua and Galleria mellonella L. Tebufenozide induced a premature and lethal larval moult in larval Lepidoptera within 24 h of treatment. Most larvae died in their old larval cuticle. Other aberrations included inhibition of weight gain and feeding, extrusion of the hindgut, loss of hemolymph and an abnormal and lethal pupation. In contrast, tebufenozide at similar doses/concentrations had no activity on larval instars of Leptinotarsa decemlineata (Say) and Diabrotica virgifera virgifera (LeConte), nymphs of Podisus sagitta (F.) and larvae of Locusta migratoria migratorioides (R. & F.). It had a chemosterilizing activity in S. exigua, resulting in a total inhibition of oviposition within two days of continuous treatment at doses of ⩾ 10 mg litre−1. On the other hand, all deposited eggs were viable. Similar effects on reproduction occurred in L. decemlineata, but at higher concentrations.
TL;DR: Analysis of the expression of three catalase genes from Nicotiana plumbaginifolia led to the identification of at least three distinct classes, which indicates that the functional organization of catalases is generally conserved in dicotyledonous plants.
Abstract: We have analyzed the expression of three catalase (Cat; EC 1.11.1.6) genes from Nicotiana plumbaginifolia by means of RNA blot and in situ hybridizations. Our data demonstrate that the expression of each catalase is associated with a particular H2O2-producing process. Cat1 appears to be specifically involved in the scavenging of photorespiratory H2O2 and is under control of a circadian rhythm, Cat2 is uniformly expressed in different organs with a cellular preference for vascular tissues, and the expression profile of Cat3 points to a role in glyoxysomal processes. Differential expression of these catalases is also manifested in response to temperature changes. DNA sequence comparison with other dicotyledonous catalases led to the identification of at least three distinct classes, which indicates that the functional organization of catalases is generally conserved in dicotyledonous plants.
TL;DR: The results suggest that the first step in biosynthesis of Nod factors is the assembly of the oligosaccharide chain.
Abstract: Nod factors are signal molecules produced by Azorhizobium, Bradyrhizobium, and Rhizobium species that trigger nodule formation in leguminous host plants. The backbone of Nod factors consists of a beta-1,4-N-acetylglucosamine oligosaccharide from which the N-acetyl group at the nonreducing end is replaced by a fatty acid. The nodABC gene products are necessary for backbone biosynthesis. By incubation of cell extracts from Azorhizobium caulinodans with radioactive uridine diphosphate-N-acetylglucosamine, Nod factor precursors were identified and characterized as beta-1,4-N-acetylglucosamine oligosaccharides. By analysis of different nod gene mutants and by expression of nodC in Escherichia coli, the N-acetylglucosaminyltransferase activity was ascribed to the NodC protein. The results suggest that the first step in biosynthesis of Nod factors is the assembly of the oligosaccharide chain.
TL;DR: The phylogenetic position and various genotypic, chemotaxonomic, and classical phenotypic characteristics of 21 gram-negative avian isolates were studied and a new taxon is proposed, for which the name Ornithobacterium rhinotracheale is proposed.
Abstract: The phylogenetic position and various genotypic, chemotaxonomic, and classical phenotypic characteristics of 21 gram-negative avian isolates were studied. These strains constitute a genotypically homogeneous taxon in rRNA superfamily V, as shown by DNA-rRNA hybridization data. Determination of the 16S rRNA sequence of this taxon revealed its detailed position within the “flavobacter” subgroup of the “flavobacter-bacteroides” phylum as described by Gherna and Woese (R. Gherna and C. R. Woese, Syst. Appl. Microbiol. 15:513-521, 1992). This new taxon is only distantly related to other members of the “flavobacter-bacteroides” phylum and is therefore given separate generic status. The DNA-DNA binding values for members of this taxon, for which we propose the name Ornithobacterium rhinotracheale, confirmed that all of the strains are highly interrelated (DNA-DNA binding values greater than 90% were measured). The G+C contents of members of this taxon are between 37 and 39 mol%. An analysis of the cellular proteins and fatty acids and classical phenotypic characteristics allowed us to distinguish O. rhinotracheale from phenotypically similar taxa, such as Riemerella anatipestifer and Capnocytophaga species. The respiratory quinone content (menaquinone 7) and carbohydrate pattern of O. rhinotracheale conform with the respiratory quinone contents and carbohydrate patterns of other members of rRNA superfamily V.
TL;DR: The role of the neutrophil granulocyte during acute coliform mastitis in cows in the periparturient period is reviewed and quantitative aspects of several neutrophils cell functions before and during experimentally induced infections are briefly discussed.
Abstract: Mammary leucocytes are the major contributors to natural defence against mastitis after a microorganism has entered the gland. This paper reviews the role of the neutrophil granulocyte during acute coliform mastitis in cows in the periparturient period. Qualitative and quantitative aspects of several neutrophil cell functions before and during experimentally induced infections are briefly discussed.
28 Nov 1994
TL;DR: The BER degradation caused by a given frequency offset between receiver and transmitter clock, as compared with the case of ideal sampling, is calculated.
Abstract: In fully digital receivers, carrier and timing information is derived from samples of the (anti-aliasing-filtered) received continuous-time signal. In case of synchronized sampling, this information is used to align the sampling clock of the receiver with the remote transmit clock. In nonsynchronized sampling systems, the sampling at the receiver is performed by means of a fixed free-running clock, and additional post-processing is necessary to perform timing correction in the digital domain. We investigate the effect of non-synchronized sampling on the BER performance of OFDM systems. We calculate the BER degradation caused by a given frequency offset between receiver and transmitter clock, as compared with the case of ideal sampling. The obtained results are compared with the performance of synchronized sampling systems.
TL;DR: It is argued that embedding the foot in a well-fitting shoe increases the effective stiffness of the heel pad by means of a high-speed two-dimensional cineradiographic registration of an actual running step.
TL;DR: The recent review of deep-sea meiofauna was discussed, which focused mainly on the abundance and biomass data from different oceans and on the relationship between the biomass of the meiobenthos and that of other faunal components.
Abstract: This chapter throws the attention on the meiobenthos of the deep northeast Atlantic. The main purpose of this chapter is to summarize new results from an area lying between 15°N and 53°N and extending from the continental margin of western Europe and northwest Africa to the Mid-Atlantic Ridge. It considers first the nature and scope of meiofaunal research in the northeast Atlantic and then discuss the environmental parameters, which are believed to influence meiofaunal organisms. This chapter then discusses the various types and scales of pattern observed among meiofaunal populations within the study area, progressing from the large-scale bathymetric and latitudinal trends and then to small-scale horizontal patterns within particular areas. Faunal densities and faunal composition are considered separately and compared with data from other regions. This chapter also deals with the distribution of meiofauna within sediment profiles and the temporal variability of populations. This chapter concludes by discussing the recent review of deep-sea meiofauna, which focused mainly on the abundance and biomass data from different oceans and on the relationship between the biomass of the meiofauna and that of other faunal components
TL;DR: In vitro study indicates that altering BSH activity can be a valid (micro) biological alternative treatment for patients with severe hypercholesterolaemia and calculated that a daily intake of a realistic amount of highly BSH active Lactobacilli cells, e.g. in the form of yoghurt, might lead to a significant reduction of cholesterol.
Abstract: Growth and bile salt hydrolase (BSH) activity of the isogenic Lactobacillus plantarum 80 (LP80) strains were studied in vitro . In pure culture experiments viability and growth performance of the BSH - LP80 strain was negatively affected by the presence of conjugated bile salts. The LP80 wild type (WT) and BSH overproducing LP80 (pCBHl) strains did not show a die-off upon supplementation of bile salts. The latter strains hydrolysed glyco-conjugated deoxycholate (GDCA) more readily than tauro-conjugated deoxycholate (TDCA), indicating substrate specificity of the enzyme. BSH activities towards TDCA of LP80 WT and LP80 (pCBHl) stationary phase cells were 0.17 and 1.02 μmol/mg CDW.h respectively; activities towards GDCA of the respective strains were 3.52 and 54.80 μmol/mg CDW.h respectively. The study of BSH activity as a function of growth revealed a marked difference in behaviour between LP80 WT and LP80 (pCBHl) with LP80 WT hydrolysing GDCA when reaching the exponential phase, whereas LP80 (pCBHl) immediately started to hydrolyse GDCA. TDCA hydrolysis increased after GDCA hydrolysis was completed. BSH activity of LP80 (pCBHl) in a mixed microbial association, resembling that of the small intestine, was comparable to that determined under pure culture conditions, indicating that BSH activity will probably not be influenced by the presence of the normal intestinal microbiota. Based on the BSH activity of LP80 (pCBHl) and on physiological data on the bile salt-cholesterol metabolism interrelationship, it was calculated that a daily intake of a realistic amount of highly BSH active Lactobacillus cells, e.g. in the form of yoghurt, might lead to a significant reduction of cholesterol. Hence, this in vitro study indicates that altering BSH activity can be a valid (micro) biological alternative treatment for patients with severe hypercholesterolaemia. Keywords - Bile salt hydrolysis, Lactobacilli, Cholesterol, Hypercholesterolaemia, Probiotic food products.
TL;DR: Daphnia is largely absent from the Tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities, considered a consequence of higher prevalent predation levels in the tropics.
Abstract: The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.
TL;DR: In this article, a review of the direct fitting procedures used in the analysis of Mossbauer spectra is presented, including direct lineshape fitting with alternative profiles as well as shape-dependent, shapeindependent and quasi shapeindependent distribution fitting methods all can easily be incorporated in one computer program scheme yielding a large versatility for modification and/or extension of the programs according to specific spectra.
Abstract: A review is presented of the direct fitting procedures which are used in the analysis of Mossbauer spectra. Direct lineshape fitting with alternative profiles as well as shape-dependent, shape-independent and quasi shape-independent distribution fitting methods all can easily be incorporated in one computer program scheme yielding a large versatility for modification and/or extension of the programs according to specific spectra.
TL;DR: The interaction of the CBD with filter paper apparently accounts for the mass-transfer-limited binding rate and also for the irreversible adsorption of intact CBH I, a component lacking the cellulose-binding domain (CBD), which is not significantly influenced by mass transfer.
Abstract: Separate binding of several purified cellulolytic components of Trichoderma reesei on to filter paper was studied and concomitant hydrolysis rates evaluated. Enhancement of mass transfer from the bulk liquid to the solid substrate by agitation has two different effects on adsorption depending on the type of enzyme: (i) the fraction of cellobiohydrolase II (CBH II) and endoglucanase III (EG III) bound at equilibrium is increased, whereas (ii) the rate but not the extent of cellobiohydrolase I (CBH I) and endoglucanase I (EG I) adsorption is affected. The adsorption of CBH I core, a component lacking the cellulose-binding domain (CBD), is, however, not significantly influenced by mass transfer. The CBH I interdomain peptide (present in CBH I core b) does not participate in adsorption but enhances stability. The adsorption of CBH I core proteins is a fully reversible process whereas that of the intact CBH I is not. Thus, the interaction of the CBD with filter paper apparently accounts for the mass-transfer-limited binding rate and also for the irreversible adsorption of intact CBH I. Adsorption isotherms at 50 degrees C indicate very similar relative association constants for the intact cellulases (0.24-0.30 l/g of cellulose), but drastically reduced values for CBH I core proteins (0.03 l/g of cellulose). The specific activities of adsorbed CBH I and of its core proteins are identical and a linear relationship between adsorption and rates of hydrolysis is found only for these enzymes. Thus, non-productive binding on to cellulose seems evident in the case of CBH II and EG III but not CBH I.
TL;DR: The sites of GUS-activity in strongly pigmented whole-mount preparations or thick handmade sections of plant material can easily be visualized by clearing it with chlorallactophenol (CLP), without affecting the ClBr-indigo precipitate.
Abstract: The sites of GUS-activity in strongly pigmented whole-mount preparations or thick handmade sections of plant material can easily be visualized by clearing it with chlorallactophenol (CLP), without affecting the ClBr-indigo precipitate.
TL;DR: The structure of the heterodimeric flavocytochrome c sulfide dehydrogenase from Chromatium vinosum was determined at a resolution of 2.53 angstroms and contains a glutathione reductase-like flavin-binding subunit and a diheme cytochrome subunit.
Abstract: The structure of the heterodimeric flavocytochrome c sulfide dehydrogenase from Chromatium vinosum was determined at a resolution of 2.53 angstroms. It contains a glutathione reductase-like flavin-binding subunit and a diheme cytochrome subunit. The diheme cytochrome folds as two domains, each resembling mitochondrial cytochrome c, and has an unusual interpropionic acid linkage joining the two heme groups in the interior of the subunit. The active site of the flavoprotein subunit contains a catalytically important disulfide bridge located above the pyrimidine portion of the flavin ring. A tryptophan, threonine, or tyrosine side chain may provide a partial conduit for electron transfer to one of the heme groups located 10 angstroms from the flavin.
TL;DR: In this article, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO2 barrier into the metal is made.
Abstract: Ultrathin oxide layers, 2– nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (RTO) at 900°C. RTO is an effective method to control the oxide thickness in this range to within 10%. The direct tunnelling through these ultrathin layers is examined with current-voltage and impedance measurements on Al/SiO2/n-Si structures with an oxide layer thickness between 2 and 4 nm. After the determination of the surface potential vs bias relation and the oxide layer capacitance from the capacitance-voltage measurements, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO2 barrier into the metal is made. A very good agreement with the theory is obtained assuming a simple trapezoidal tunnel barrier for the SiO2, from which the tunnel barrier height and the electron effective mass in the SiO2 bandgap are derived. The density of interface traps at the Si/SiO2 interface is determined using the conductance method. Only a very small increase of interface trap density with decreasing oxide layer thickness is found. The very high density of interface traps (more than 3 × 1012 cm−2 eV−1) can be reduced to the 1010 cm−2 eV−1 level by application of a conventional Post Metallization Anneal (PMA).
TL;DR: This study supports the use of a selected battery of tests to evaluate ecotoxicity and suggests its possible importance for screening of biologically-active compounds from natural sources.
Abstract: The acute toxicity data of the first 50 chemicals of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme is compared for three “cyst-based toxicity tests” (Artoxkit M with Artemia salina, Streptoxkit F with Streptocephalus proboscideus, and Rotoxkit F with Brachionus calyciflorus), and two other tests (the Daphnia magna and the Photobacterium phosphoreum Microtox™ tests) commonly used in ecotoxicology. The difference in sensitivity for the 50 chemicals was as high as 19 orders of magnitude (on a molecular weight basis) between the most and least sensitive species. Generally, a similar toxicity ranking of the 5 test species was found for most of the chemicals and the interspecies correlations were high. Results from Principal Component Analysis (PCA) and cluster analysis indicated that the groupings are not related to a clear and defined chemical structure. However, the loading plot of the first two principal components may aid in selecting the minimum number and type of tests that have to be included in a battery which encompasses a broad spectrum of toxicity levels. Consequently, this study supports the use of a selected battery of tests to evaluate ecotoxicity and suggests its possible importance for screening of biologically-active compounds from natural sources.
TL;DR: It is demonstrated that subjecting postlarvae to reduced salinities for 2h provides a simple and rapid test for assaying the physiological condition of postlarval shrimp and suggests that an excessive supply of n-3 may not be beneficial to the shrimp.
01 Jan 1994
TL;DR: A procedure is developed for clustering objects in a low-dimensional subspace of the column space of an objects by variables data matrix based on the K-means criterion and seeks the subspace that is maximally informative about the clustering structure in the data.
Abstract: A procedure is developed for clustering objects in a low-dimensional subspace of the column space of an objects by variables data matrix. The method is based on the K-means criterion and seeks the subspace that is maximally informative about the clustering structure in the data. In this low-dimensional representation, the objects, the variables and the cluster centroids are displayed jointly. The advantages of the new method are discussed, an efficient alternating least-squares algorithm is described, and the procedure is illustrated on some artificial data.
01 Jan 1994
TL;DR: Lactic acid bacteria are Gram-positive non-sporing cocci, coccobacilli or rods, having a DNA base composition of less than 50 mol% G + C, and they generally lack catalase.
Abstract: Lactic acid bacteria are Gram-positive non-sporing cocci, coccobacilli or rods, having a DNA base composition of less than 50 mol% G + C. They generally lack catalase, although pseudo-catalase was detected in cultures grown on a low sugar concentration, and they need a fermentable carbohydrate for growth. Glucose is converted mainly to lactic acid (homofermentatives), or to lactic acid, carbon dioxide, ethanol and/or acetic acid (heterofermentatives). The branches within lactic acid bacteria do not completely agree with the traditional classification schemes based on morphology and phenotypic characteristics. Lactic acid bacteria comprise the genera Aerococcus, Alloiococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, Streptococcus, Tetragenococcus, and Vagococcus. The genus Bifidobacterium will also be briefly considered here, although phylogenetically it belongs to the Actinomycetes subdivision of the Gram-positive eubacteria, comprising also Propionibacterium, Brevibacterium and the microbacteria. The latter taxa are only very distantly related to the genuine lactic acid bacteria.