The electro-optical investigation of suspensions of Escherichia coli K-12 cells metabolizing glucose,lactose, and galactose

The electro-optical characteristics of suspensions of Escherichia coli K-12 cells metabolizing glucose, lactose, and galactose were studied my measuring the suspension turbidity as a function of cell alignment in an orienting electric field whose frequency was varied from 10 kHz to 10 MHz. In a frequency range of 10 kHz to 1 MHz, the orientational spectra of E. coli K-12 cells grown on glucose and lactose considerably changed after their incubation in the presence of the sugars. These changes likely reflect alterations in the polarizability of the cells induced by sugar metabolism.     

Influence of plant species on population dynamics, genotypic diversity and antibiotic production in the rhizosphere by indigenous Pseudomonas spp

The population dynamics, genotypic diversity and activity of naturally-occurring 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. was investigated for four plant species (wheat, sugar beet, potato, lily) grown in two different soils. All four plant species tested, except lily and in some cases wheat, supported relatively high rhizosphere populations (5 x 10(4) to 1 x 10(6) CFU/g root) of indigenous DAPG-producing Pseudomonas spp. during successive cultivation in both a take-all suppressive and a take-all conducive soil. Although lily supported on average the highest population densities of fluorescent Pseudomonas spp., it was the least supportive of DAPG-producing Pseudomonas spp. of all four plant species. The genotypic diversity of 492 DAPG-producing Pseudomonas isolates, assessed by Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the phlD gene, revealed a total of 7 genotypes. Some of the genotypes were found only in the rhizosphere of a specific plant, whereas the predominant genotypes were found at significantly higher frequencies in the rhizosphere of three plant species (wheat, sugar beet and potato). Statistical analysis of the phlD(+) genotype frequencies showed that the diversity of the phlD(+) isolates from lily was significantly lower than the diversity of phlD(+) isolates found on wheat, sugar beet or potato. Additionally, soil type had a significant effect on both the phlD(+) population density and the phlD(+) genotype frequencies, with the take-all suppressive soil being the most supportive. HPLC analysis further showed that the plant species had a significant effect on DAPG-production by the indigenous phlD(+) population: the wheat and potato rhizospheres supported significantly higher amounts of DAPG produced per cell basis than the rhizospheres of sugar beet and lily. Collectively, the results of this study showed that the host plant species has a significant influence on the dynamics, composition and activity of specific indigenous antagonistic Pseudomonas spp.     

The Electro-Optical Investigation of Suspensions of Escherichia coli K-12 Cells Metabolizing Glucose,Lactose, and Galactose

The electro-optical characteristics of suspensions of Escherichia coli K-12 cells metabolizing glucose, lactose, and galactose were studied by measuring the suspension turbidity as a function of cell alignment in an orienting electric field whose frequency was varied from 10 kHz to 10 MHz. In a frequency range of 10 kHz to 1 MHz, the orientational spectra of E. coli K-12 cells grown on glucose and lactose considerably changed after their incubation in the presence of the sugars. These changes likely reflect alterations in the polarizability of the cells induced by sugar metabolism.     

Continuous dielectrophoretic separation of cell mixtures.

Use of stream-centered dielectrophoresis (1-4) produced continuous separations on three cell mixtures (1) Chorella vulgaris with Netrium digitus, (2) Ankistrodesmus falcatus with Staurastrum gracile, and (3) Saccharomyces cerevisiae with Netrium digitus. Maximal separations were obtained for these mixtures of live cells at 100 kHz, 600 kHz, and 2.0 MHz, respectively. The technique was restricted to a frequency range of 0.01-32 MHz, and to suspensions of low conductivity in which microorganisms such as these algae and yeast are tolerant. Extension, however, to cellular organisms requiring higher osmolarity is readily feasible through the use of nonionic solutes such as sucrose, mannose, glycine, etc.     

Effects of high dietary fibre diets formulated from by-products from vegetable and agricultural industries on plasma metabolites in gestating sows

The aim of the present study was to examine the biochemical influence of feeding high dietary fibre (DF) diets formulated from by-products from the vegetable and agricultural industries to sows during early to mid-gestation. The effect of feeding frequency (once vs. twice daily) on diurnal plasma metabolites patterns was also examined. The study included a total of 48 gestating sows from four blocks (12 gestating sows in each block). The sows were fed four different diets containing varying levels of starch (304-519 g/kg dry matter (DM)) and DF (171-404 g/kg DM) but with equal amounts of net energy. The low-DF diet (control) was based on barley and wheat, and the three high-DF diets formulated by replacing barley and wheat by pectin residue, sugar beet pulp and potato pulp, respectively. The experimental design comprised two periods of 4 weeks each. Half the sows were fed once daily at 08:00 h in the first period and twice daily at 08:00 and 15:00 h during the second period, and vice versa for the other half of the sows. Plasma samples from vena jugularis were collected by venipuncture at 07:00, 09:00, 12:00 and 19:00 h. Feeding high-DF increased plasma short-chain fatty acids (p = 0.02) and non-esterified fatty acids (p < 0.001). However, there was no clear effect of DF on glucose and insulin responses. A negative correlation between amount of DF in the diets and plasma creatine (R2 = 1.00; diet effect: p = 0.02) suggested that plasma creatine concentrations was an indicator for the level of glucose-glycogen interchange. Furthermore, an explorative approach using nuclear magnetic resonance spectroscopy-based metabonomics identified betaine (p < 0.001), dimethyl sulfone (DMSO2; p < 0.001) and scyllo-inositol (p < 0.001) as biomarkers for the different by-products; pectin residue was related to high plasma levels of DMSO2, sugar beet pulp to plasma betaine, DMSO2 and scyllo-inositol, and potato pulp to plasma DMSO2 and scyllo-inositol. In conclusion, replacing starch by DF affected surprisingly few metabolites in peripheral plasma. No negative effects were found in feeding pectin residue, sugar beet pulp or potato pulp for gestating sows as judged from the minor metabolic changes.     

Beet leafhopper (Hemiptera: Cicadellidae) settling behavior, survival, and reproduction on selected host plants

Experiments were conducted to determine the settling behavior, survival, and reproduction of the beet leafhopper, Circulifer tenellus (Baker), when maintained on selected host plants. This leafhopper was recently identified in the Columbia Basin of Washington and Oregon as the probable vector of the beet leafhopper-transmitted virescence agent phytoplasma, causal agent of several vegetable crop diseases, including potato purple top. Plants selected for study were sugar beet, Beta vulgaris L.; radish, Raphanus sativus L.; dry bean, Phaseolus vulgaris L.; potato, Solanum tuberosum L.; carrot, Daucus carota L.; and tomato, Lycopersicon esculentum Mill. Leafhopper adults were confined on caged plants, and settling behavior was observed during a 72-h period and survival was monitored for 40 d. Also, oviposition and nymphal production were investigated by maintaining leafhoppers for approximately 90 d on each of the selected plants. Sixty to 100% of leafhoppers settled on all studied plants during the first 5 h, but settling on bean and tomato declined sharply thereafter. Leafhopper mortality was very high on bean and tomato, with 95 and 65% of the leafhoppers, respectively, dying in about a week. In contrast, 77, 90, and 95% of leafhoppers maintained on potato, sugar beet, and radish, respectively, survived until the end of the 40-d experimental period. Beet leafhopper oviposition and nymphal production and development only occurred on sugar beet, radish, and potato; reproduction was lower on potato.     

Ensiled sugar beets as dietary component and their effect on preference and dry matter intake by goats

This study examines the influence of ensiled sugar beets (Beta vulgaris ssp. vulgaris) on preference and short-time dry matter (DM) intake of goats. Whole sugar beets were ensiled either without any silage additive (sugar beet silage (SBS)) or with a chemical additive (6 l/t) containing 85% formic and propionic acids (treated sugar beet silage (TBS)) and were chopped after ensiling. The influence of different proportions of SBS (0%, 6.25%, 12.5%, 18.75% and 25% of dietary DM) and TBS (0%, 5%, 10%, 15% and 20% of DM) in partial mixed rations on short-time DM intake by goats (adult Saanen type wethers; n = 10) was studied in two separate, independent trials. Preference behaviour was investigated by offering the goats two different experimental diets per day and offer each possible combination of them (n = 10) once throughout the trial. On this basis, the mean DM intake (within 30 min and 3 h) of each experimental diet was determined. Both sugar beet silages showed good fermentation quality with low pH. By using the chemical silage additive, the production of ethanol was reduced and considerable amounts of sugar were preserved. In the short-term preference experiment, increasing concentrations of sugar beet silage in the ration increased DM intake (p < 0.05) in a linear way with a strong preference for those diets containing high amounts of sugar beet silage. Initial DM intake after 30 min was 4–5 fold increased for diets containing the highest beet concentration. It is assumed that the preference was positively influenced by sugar and sweet taste or the associated higher concentration of metabolisable energy.     

Scale up of fuel ethanol production from sugar beet juice using loofa sponge immobilized bioreactor

Production of fuel ethanol from sugar beet juice, using cells immobilized on loofa sponge was investigated. Based on ethanol productivity and ease of cell immobilization, a flocculating yeast strain, Saccharomyces cerevisiae IR2 was selected for ethanol production from sugar beet juice. It was found that raw sugar beet juice was an optimal substrate for ethanol production, requiring neither pH adjustment nor nitrogen source supplement. When compared with a 2 l bubble column bioreactor, mixing was not sufficient in an 8 l bioreactor containing a bed of sliced loofa sponges and consequently, the immobilized cells were not uniformly distributed within the bed. Most of the cells were immobilized in the lower part of the bed and this resulted in decreased ethanol productivity. By using an external loop bioreactor, constructing the fixed bed with cylindrical loofa sponges, dividing the bed into upper, middle and lower sections with approximately 1 cm spaces between them and circulating the broth through the loop during the immobilization, uniform cell distribution within the bed was achieved. Using this method, the system was scaled up to 50 l and when compared with the 2 l bubble column bioreactor, there were no significant differences (P > 0.05) in ethanol productivity and yield. By using external loop bioreactor to immobilize the cells uniformly on the loofa sponge beds, efficient large scale ethanol production systems can be constructed.     

Invertase inhibitors from red beet, sugar beet, and sweet potato roots

Invertase inhibitors have been isolated and partially purified from red beets, sugar beets, and sweet potatoes. These inhibitors are thermolabile proteins with molecular weights of 18,000 to 23,000. They do not inhibit yeast and Neurospora invertases, but they are reactive with potato tuber invertase and other plant invertases with pH optima near 4.5. There are differences in reactivity of the inhibitors with some of the plant invertases, however. For most invertases, red beet and sugar beet inhibitors are most effective at pH 4.5 while sweet potato inhibitor is most effective at pH 5.     

Experimental investigation on neural cell survival after dielectrophoretic trapping

Negative dielectrophoretic forces can effectively be used to trap cortical rat neurons. The creation of dielectrophoretic forces requires electric fields of high non-uniformity. High electric field strengths, however, can cause excessive membrane potentials by which cells may unrecoverably be changed or it may lead to cell death. In a previous study it was found that cells trapped at 3 Vtt/14 MHz did not change morphologically as compared to cells that were not exposed to the electric field. This study investigates the viability of fetal cortical rat neurons after being trapped by negative dielectrophoretic forces at frequencies up to 1 MHz. A planar quadrupole micro-electrode structure was used for the creation of a non-uniform electric field. The sinusoidal input signal was varied in amplitude (3 and 5 Vtt) and frequency (10 kHz-1 MHz). The results presented in this paper show that the viability of dielectrophoretically trapped postnatal cortical rat cells was greatly frequency dependent. To preserve viability frequencies above 100 kHz (at 3 Vtt) or 1 MHz (5 Vtt) must be used.     

Continuous dielectrophoretic separation of cell mixtures

Use of stream-centered dielectrophoresis (1–4) produced continuous separations on three cell mixtures (1)Chlorella vulgaris withNetrium digitus, (2)Ankistrodesmus falcatus withStaurastrum gracile, and (3)Saccharomyces cerevisiae withNetrium digitus. Maximal separations were obtained for these mixtures of live cells at 100 kHz, 600 kHz, and 2.0 MHz, respectively. The technique was restricted to a frequency range of 0.01–32 MHz, and to suspensions of low conductivity in which microorganisms such as these algae and yeast are tolerant. Extension, however, to cellular organisms requiring higher osmolarity is readily feasible through the use of nonionic solutes such as sucrose, mannose, glycine, etc.     

Carbon balances for in vitro digestion and fermentation of potential roughages for pregnant sows

Ad libitum feeding of pregnant sows requires satiating, intake-restricting feed components to prevent sows from getting excessively fat. Because hindgut fermentation starts only after and proceeds much slower than enzymatic digestion in the small intestine, fermentation products might, as nutrients, induce a prolonged physiological satiation of sows. To simulate hindgut fermentation and determine the fermentative release of short-chain fatty acids (SCFA) in vitro, gas production tests (GPTs) were performed with different raw materials after removal of enzymatically hydrolysable compounds. Fresh feces from sows that received standard sow feed was used as inoculum. Fresh, ensiled, or dehydrated by-products of the food industry (brewers’ grains, liquid yeast feed, maize gluten feed, raw potato chips, potato steam peel, pressed potato pulp, sugar beet pulp (SBP)) and whole-plant products (grass, maize) were tested as individual products.

Balances were drawn up of the in vitro flow of organic carbon (OC) to an “ileal” nutrient fraction, a “hindgut” fraction of SCFA and gas, and “fecal” remnants. The OC balances revealed large variations among raw materials in terms of their contribution to the different fractions. Potato steam peel gave the largest “ileal” nutrient fraction (77% of total OC), the lowest was observed with fresh sugar beet pulp (9% of total OC). In the GPT, SBP, and potato pulp brought about the highest “hindgut” SCFA yields (32–49% of total OC), and together with raw potato chips, the highest amounts of gas. Grass products and liquid yeast feed were slower fermented than most by-products. Moreover, whole-plant materials gave larger “fecal” OC portions than by-products, with the exception of fresh and dehydrated brewer’s grains. Together with straw, the latter were the least degradable of all raw materials tested. Among the grass products, dehydrated grass, and among the by-products, raw potato chips left the least “fecal” residues, i.e. they were nutritionally utilized to the largest extent.     

Isolation and NMR characterisation of a (4-O-methyl-D-glucurono)-D-xylan from sugar beet pulp

Stable aqueous suspensions of purified and homogenised sugar beet pulp (SBP) cellulose were subjected to various TFA treatments which induced a flocculation of the suspension and the release of a number of polysaccharides. Among these, a 4-O-methyl glucuronoxylan was isolated and characterized by 1H and 13C NMR spectroscopy. In this polysaccharide the molar proportions of D-Xyl and 4-O-Me-D-GlcA were found to be 7:1. The presence of a glucuronoxylan at the surface of the cellulose microfibrils is very likely involved in the stability of the suspensions. To our knowledge, the presence of a 4-O-methyl-glucuronoxylan in the sugar beet cells has not been described previously.     

In-situ biomass characterisation by impedance spectroscopy using a full-bridge circuit

A full-bridge sensor system for characterising biosuspensions by impedance spectroscopy which avoids cross-sensitivity to temperature is presented. To record a large range of different kinds of cells, frequency is varied between 500 kHz and 50 MHz. The characteristic frequencies of the #-polarisation of animal cells (mouse), yeasts (Saccharomyces cerevisiae) and Escherichia coli bacteria are located in this range. The widespread applicability of this method is demonstrated by measurements on suspensions of different cells and the determination of concentration in a fermentation process. Furthermore, yeast suspensions are characterised at temperatures between T₁=24°C and T₂=36°C to evaluate the influence of temperature. A reduction of cross-sensitivity of about one order of magnitude compared to a single-sensor results. Changing in the conductivity of the suspension by 26% alters the measured biomass concentration by only 2.8%.     

Filtration of bacteria and yeast by ultrasound-enhanced sedimentation

Continuous flow filtration of suspensions of eukaryotic cells by ultrasonic standing wave enhanced sedimentation has recently been reported. The filtration efficiency for Escherichia coli in such a filter has been characterized at frequencies of 1 and 3 MHz in the present work and compared with results for Saccharomyces cerevisiae. The yeast can be filtered at greater than 99% efficiency at a flow rate of 5 ml min^-1 at either frequency. The filtration efficiency of the smaller E. coli at 3 MHz is in excess of 80% at concentrations in the region of 10¹⁰ mI^-1 but decreased at lower concentrations. However, E. coli in a mixed suspension with yeast were, because of inter-particle interactions, removed with the filtrate at an efficiency ranging from 80 to 50% over the eight orders of bacterial concentrations tested (down to 10³ mI^-1) at 3 MHz. Quantitative considerations show that poor filtration of pure suspensions of the smaller cells at the lower frequency arises because, at reasonable flow rates, the residence time is not sufficient for the cells to reach the pressure nodal cell concentration regions. The filtration efficiencies of both cell types are comparable at 3 MHz. It is suggested that the more comparable efficiencies arise because concentration regions are narrower at the high frequency and Stokes drag by the filter bulk flow inhibits sedimentation of the concentrated cells.     

Glucose transport activity in isolated plasma membrane vesicles from Saccharomyces cerevisiae

Purified plasma membranes prepared from yeast cells by mechanical agitation with glass beads exhibit no detectable sugar transport activity. However, the addition of phospholipid (asolectin) liposomes to the purified plasma membranes followed by freezing, thawing, and brief sonication produces membrane vesicles which exhibit D-glucose-specific transport activity. The characteristics of zero trans, equilibrium exchange, and influx counterflow exhibited by the membrane vesicles are similar to those of intact cells.     

Sugar Beet Juice Fermentation by Zymomonas mobilis Attached to Stainless Steel Wire Spheres

The fermentation of sugar beet juice as well as juice syrup medium by Zymomonas mobilis inoculum attached to stainless steel wire spheres was investigated. A semi‐synthetic sucrose medium enriched with mineral salts and yeast extract was used as the control. It was established that raw sugar beet juice ensured good Zymomonas mobilis culture growth and slightly decreased ethanol synthesis applying both flame‐burned and TiCl₄‐treated wire spheres as carriers (Q_x = 0.05—0.06 g/l × h; Q_eth = 1.02—1.22 g/l × h). High ethanol yield was also observed in juice medium (Y = 0.45‐0.46 g/g), however, levan synthesis with this medium decreased. The application of juice syrup brought about less growth effect and ethanol synthesis as compared to juice medium. The use of semi‐synthetic sucrose medium resulted in high levan production (Q_lev = 0.6—0.7 g/l × h), however, reduced ethanol production by 40%. In conclusion, sugar beet juice or syrup is recommendable for the preparation of Zymomonas mobilis inoculum. The levan production stage has to be realized using an optimized semi‐synthetic sucrose medium. The installed wire spheres filled with inocula provided the possibility for a repeated batch fermentation process, which could be recommended for both juice and semi‐synthetic sucrose medium fermentation.     

Fate of Clavibacter michiganensis ssp. sepedonicus, the Causal Organism of Bacterial Ring Rot of Potato, in Weeds and Field Crops

Crops and weeds were tested for their ability to host Clavibacter michiganensis ssp. sepedonicus (Cms), the causal agent of bacterial ring rot in potato. Ten crops grown in rotation with potato in Europe, namely maize, wheat, barley, oat, bush bean, broad bean, rape, pea and onion and five cultivars of sugar beet were tested by stem and root inoculation. About 6–8 weeks after inoculation, Cms could be detected in most crops except onion and sugar beet, in larger numbers in stems (10⁵–10⁶ cells/g of tissue) than in roots (≤10³ cells/g of tissue) in immunofluorescence cell‐staining (IF). Cms was successfully re‐isolated only from IF‐positive stem samples of maize, bush bean, broad bean, rape and pea, but not from roots. Twelve solanaceous weeds and 13 other weeds, most commonly found in potato fields in Europe, were tested in IF as hosts of Cms by stem and root inoculations. Only in Solanum rostratum, a weed present in northern America, Cms persisted in high numbers (10⁸ cells/g tissue) in stems and leaves, where it caused symptoms. In the other solanaceous weeds, Cms persisted at low numbers (approximately 10⁵ cells/g of tissue) in stems but less so in roots. The bacteria could be frequently re‐isolated from stem but not from root tissues. In 2 consecutive years, plants from 14 different weed species were collected from Cms‐contaminated potato field plots and tested for the presence of Cms by dilution plating or immunofluorescence colony‐staining (IFC), and by AmpliDet RNA, a nucleic acid‐based amplification method. Cms was detected in roots but not in stems of Elymus repens plants growing through rotten potato tubers, and in some Viola arvensis and Stellaria media plants, where they were detected both in stems and roots, but more frequently by AmpliDet RNA than by IFC.