Effect of Sugar Concentration in Jerusalem Artichoke Extract on Kluyveromyces marxianus Growth and Ethanol Production

The effect of inulin sugars concentration on the growth and ethanol production by Kluyveromyces marxianus UCD (FST) 55-82 was studied. A maximum ethanol concentration of 102 g/liter was obtained from 250 g of sugars per liter initial concentration. The maximum specific growth rate varied from 0.44 h⁻¹ at 50 g of sugar per liter to 0.13 h⁻¹ at 300 g of sugar per liter, whereas the ethanol yield remained almost constant at 0.45 g of ethanol per g of sugars utilized.     

Information Transfer in Gonadotropin-releasing Hormone (GnRH) Signaling: EXTRACELLULAR SIGNAL-REGULATED KINASE (ERK)-MEDIATED FEEDBACK LOOPS CONTROL HORMONE SENSING*

Cell signaling pathways are noisy communication channels, and statistical measures derived from information theory can be used to quantify the information they transfer. Here we use single cell signaling measures to calculate mutual information as a measure of information transfer via gonadotropin-releasing hormone (GnRH) receptors (GnRHR) to extracellular signal-regulated kinase (ERK) or nuclear factor of activated T-cells (NFAT). This revealed mutual information values <1 bit, implying that individual GnRH-responsive cells cannot unambiguously differentiate even two equally probable input concentrations. Addressing possible mechanisms for mitigation of information loss, we focused on the ERK pathway and developed a stochastic activation model incorporating negative feedback and constitutive activity. Model simulations revealed interplay between fast (min) and slow (min-h) negative feedback loops with maximal information transfer at intermediate feedback levels. Consistent with this, experiments revealed that reducing negative feedback (by expressing catalytically inactive ERK2) and increasing negative feedback (by Egr1-driven expression of dual-specificity phosphatase 5 (DUSP5)) both reduced information transfer from GnRHR to ERK. It was also reduced by blocking protein synthesis (to prevent GnRH from increasing DUSP expression) but did not differ for different GnRHRs that do or do not undergo rapid homologous desensitization. Thus, the first statistical measures of information transfer via these receptors reveals that individual cells are unreliable sensors of GnRH concentration and that this reliability is maximal at intermediate levels of ERK-mediated negative feedback but is not influenced by receptor desensitization.     

Kinetics of ethanol production by immobilized cells of Zymomonas mobilis at varying d-glucose concentrations

Ethanol fermentation by cells of Zymomonas mobilis immobilized in calcium alginate gel has been studied using 5 to 30 wt% initial d-glucose in the medium. Up to 27% d-glucose was completely fermented and the maximum ethanol concentration of 12.6% (w/v) was obtained using an immobilized cell concentration of 58 g dry wt l^?1 of bead volume. The ethanol yield coefficient was almost unaffected by initial d-glucose concentration and its value was >95% of theoretical. The rates of ethanol production and d-glucose utilization first increased, with an increase in initial d-glucose concentration up to 13.6%, and then started to decrease upon a further increase in initial d-glucose concentration. Cell leakage from the calcium alginate beads was very low.     

A new kinetic model of protein adsorption on suspended anion-exchange resin particles.

The kinetics of adsorption of bovine serum albumin on an anion-exchange resin were measured in a batch system using a flow cell and ultraviolet absorbance, as a function of initial liquid-phase protein concentration and solid-to-liquid phase ratio. A new mathematical model for adsorption kinetics is presented that fits the experimental data to give a highly linear relationship with time, following a short transient period. Numerical integration of the differential form of the new composite nonlinear (CNL) kinetic model, containing three independent parameters, is shown to describe the dynamics of batch adsorption much better than alternative lumped parameter models. Although the new model is phenomenological rather than mechanistic, its principal parameter is shown to be a direct linear function of a physically measurable quantity. This study demonstrates that the model can accurately simulate protein concentration-time profiles using parameter estimates derived from correlations over a wide range of initial protein concentrations and phase ratios. The new CNL model is shown to be considerably superior to the Langmuir and solid-film linear kinetic models in this regard, having the additional advantage that an equilibrium isotherm for the system is not required.     

Three-dimensional reconstruction of innermost chorion layer from Drosophila melanogaster

A low-resolution three-dimensional structure of the crystalline innermost chorion layer (ICL) has been calculated from electron microscope images of tilted negatively stained crystals. The isolated ICL is a single layer, about 12 nm thick and appears to be made up of two types of subunits, each approximately 3 nm in diameter, arranged regularly as groups of four heterodimers in space group C222. Linking density between these groups of subunits, maintaining the integrity of the layer, appears to be confined mainly to the outer surfaces of the ICL.     

The egg-shell of Drosophila melanogaster. VI, Structural analysis of the wax layer in laid eggs

Utilizing freeze-fracturing conventional electron microscopy and scanning electron microscopy methods, a wax layer was identified, sealing the oocyte of Drosophila melanogaster. In mature egg-shells wax forms a hydrophobic layer surrounding the oocyte and lying between, and in very close contact with the vitelline membrane (interiorly) and the crystalline intermediate chorionic layer (exteriorly). In cross-fractured views it is less than 50 A thick whereas in longitudinal fracturing it reveals smooth fracture faces of a multilayered material in the form of hydrophobic areas or plaques (0.5-1 microns in diameter) which are partially overlapping and highly compressed between the vitelline membrane and the innermost chorionic layer. The evidence for this layer being a wax are the facts that a) it is not preserved in conventional fat-extracting electron microscopy methods, b) it directs laterally the fracture planes during freeze-fracturing and reveals smooth fracture faces. Analysis of the structural features of wax in mature egg-shell in various species of Drosophilidae have shown that the wax layer exhibits indistinguishable (among the species) hydrophobic plaques, which have the same size and thickness with Drosophila melanogaster. These data provide structural evidence explaining the physiological resistance of the insect eggs studied, against water loss or water uptake, whenever they are laid on substrates with extreme environmental conditions. In addition, the data demonstrate how an extracellular substance can be organized to perform that function.     

Ethanol Inhibition Kinetics of Kluyveromyces marxianus Grown on Jerusalem Artichoke Juice

The kinetics of ethanol inhibition on cell growth and ethanol production by Kluyveromyces marxianus UCD (FST) 55-82 were studied during batch growth. The liquid medium contained 10% (wt/vol) inulin-type sugars derived from an extract of Jerusalem artichoke (Helianthus tuberosus) tubers, supplemented with small amounts of Tween 80, oleic acid, and corn steep liquor. Initial ethanol concentrations ranging from 0 to 80 g/liter in the liquid medium were used to study the inhibitory effect of ethanol on the following parameters: maximum specific growth rate (μ_max), cell and ethanol yields, and sugar utilization. It was found that as the initial ethanol concentration increased from 0 to 80 g/liter, and maximum specific growth rate of K. marxianus cells decreased from 0.42 to 0.09 h⁻¹, whereas the ethanol and cell yields and sugar utilization remained almost constant. A simple kinetic model was used to correlate the μ_max results and the rates of cell and ethanol production, and the appropriate constants were evaluated.     

Mixing time and oxygen transfer characteristics of double draft tube airlift fermentor

Despite the increasing importance of airlift fermentors, very little published information is available on how the geometric configurations of the draft tubes and the air-sparging system affect the mixing and oxygen transfer characteristics of the fermentor. A 14-L air-lift fermentor was designed and build with a fixed liquid height to diameter ratio of 1.5 utilizing four equally spaced air jets at the bottom. Two jet orifice sizes were used, 1.27 and 3.81 mm i.d., and for each jet size the following four geometric configurations were used: Single inner concentric draft tube, single outer concentric draft tube, two concentric draft tubes, and no draft tubes where the fermentor was operated as a shallow bubble column. It was found that the presence of draft tubes stabilized liquid circulation patterns and gave systemically higher mixing times than those obtained in the absence of draft tubes. In addition, the double draft tube geometry resulted in higher mixing times than the single draft tubes. For the power unit volume range 20 to about 250 W/m³ the larger 3.81-mm orifices gave systemically higher k_L a values than the smaller 1.27-mm i.d. orifices. At 200 W/m³ the use of a single outer draft tube with the 3.81-mm orifices resulted in 94% increase in k_L a values over that obtained with no draft tubes. However, the effect of draft tube geometry on k_L a values when the 1.27-mm orifices were used was not significant. The air bubble formation characteristics at the jet orifices were found to be different, which reflected the differences observed in mass transfer and mixing characteristics. The power economy for oxygen transfer was found to be depend strongly on the orifice size and less on the geometric configuration of draft tubes.     

Isolation and Screening of Yeasts That Ferment d-Xylose Directly to Ethanol

Natural habitats of yeasts were examined for the presence of strains able to produce ethanol from d-xylose. Black knots, insect frass, and tree exudates were screened by enrichment in liquid d-xylose-yeast extract medium. These and each d-xylose-assimilating yeast in a collection from cactus fruits and Drosophila spp. were tested for alcohol production from this sugar. Among the 412 isolates examined, 36 produced more than 1 g of ethanol liter from 20 g of d-xylose liter, all under aerated conditions. Closer examination of the strains indicated that their time courses of d-xylose fermentation followed different patterns. Some strains produced more biomass than ethanol, and among these, ethanol may or may not be assimilated rapidly after depletion of d-xylose. Others produced more ethanol than biomass, but all catabolized ethanol after carbohydrate exhaustion. Ethanol production appeared best at low pH values and under mild aeration. Possible correlations between the nutritional profiles of the yeasts and their ability to produce ethanol from d-xylose were explored by multivariate analysis. d-Xylose appeared slightly better utilized by yeasts which rate poorly in terms of fermentation. The fermentation of d-glucose had no bearing on d-xylose fermentation. No specific nutritional trait could discriminate well between better d-xylose fermentors and other yeasts.