Growth of filamentous fungi in submerged culture: problems and possible solutions

Filamentous fungi are important organisms industrially and continue to attract research interest as microbiologists attempt to overcome the problems associated with their behavior in submerged culture. This review critically examines the literature describing these problems and where available suggests possible solutions to them. The influence of the chemical and physical environment on culture morphology, the process engineering challenges presented by different fungal morphologies, and the relationship between fungal morphology and metabolite production are all discussed.

Structure of epiglucan, a highly side-chain/branched (1 --> 3;1 --> 6)-beta-glucan from the micro fungus Epicoccum nigrum Ehrenb. ex Schlecht

The extracellular fungal polysaccharide, epiglucan, synthesised by Epicoccum nigrum is a side-chain/branched (1 --> 3;1 --> 6)-D-beta-glucan. Methylation analysis, 13C DEPT NMR and specific enzymic digestion data show slight variation in branching frequency among the epiglucans from the three strains examined. The (1 --> 3)-beta-linked backbone has (1 --> 6)-beta-linked branches at frequencies greater than the homologous glucans, scleroglucan and schizophyllan, from Sclerotium spp. and Schizophyllum commune, respectively. The structural analyses do not allow a distinction to be made between structures I and II. [structures: see text] Epiglucan displays non-Newtonian shear thinning rheological properties, typical of these glucans.

Determination of the recombination correction factorkSfor some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams

It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.

Lipoprotein(a), type 2 diabetes and vascular risk in coronary patients

BACKGROUND

Lipoprotein(a) [Lp(a)] is an important cardiovascular risk factor in the general population. However, prospective data on the vascular risk conferred by Lp(a) in patients with diabetes mellitus are scarce and controversial. It is not known whether the diabetic state affects the association of Lp(a) with vascular events among coronary patients.

DESIGN

We measured Lp(a) in 587 consecutive patients undergoing coronary angiography for the evaluation of coronary artery disease. The incidence of vascular events was recorded over 4 years.

RESULTS

At baseline, Lp(a) was significantly lower in patients with type 2 diabetes (T2DM) (n = 136) than in nondiabetic individuals (11 (0.8-30) mg dL(-1) vs. 16 (0.8-51) mg dL(-1); P = 0.025). Prospectively, Lp(a) was a strong and independent predictor of vascular events in nondiabetic patients (standardized adjusted hazard ratio (HR) = 1.461 (1.121-1.904); P = 0.005), but not in patients with T2DM [HR = 0.812 (0.539-1.223); P = 0.320]. An interaction term diabetes x Lp(a) was significant (P = 0.008), indicating that Lp(a) was a significantly stronger predictor of vascular events in nondiabetic patients than in patients with T2DM.

CONCLUSIONS

Lp(a) in diabetic coronary patients is low and not associated with the incidence of vascular events. Although measurement of Lp(a) provides useful information in nondiabetic coronary patients, it is of little value in coronary patients with T2DM.

Pores in bilayer membranes of amphiphilic molecules: coarse-grained molecular dynamics simulations compared with simple mesoscopic models

We investigate pores in fluid membranes by molecular dynamics simulations of an amphiphile-solvent mixture, using a molecular coarse-grained model. The amphiphilic membranes self-assemble into a lamellar stack of amphiphilic bilayers separated by solvent layers. We focus on the particular case of tensionless membranes, in which pores spontaneously appear because of thermal fluctuations. Their spatial distribution is similar to that of a random set of repulsive hard disks. The size and shape distribution of individual pores can be described satisfactorily by a simple mesoscopic model, which accounts only for a pore independent core energy and a line tension penalty at the pore edges. In particular, the pores are not circular: their shapes are fractal and have the same characteristics as those of two-dimensional ring polymers. Finally, we study the size-fluctuation dynamics of the pores, and compare the time evolution of their contour length to a random walk in a linear potential.

Computed tomography densitometry of the lung: a method to assess perfusion defects in acute pulmonary embolism

OBJECTIVE

To evaluate the potential of spiral computed tomography (CT) densitometry of the lung to assess segmental perfusion defects in patients with acute pulmonary embolism.

MATERIALS AND METHODS

Ten patients with known segmental or lobar perfusion defects on ventilation/perfusion scintigraphy and with normal findings in the contralateral lung segment underwent spiral CT of the thorax before and after the administration of contrast material. Regions of interest were defined in 14 segments with normal perfusion and in 14 segments with reduced perfusion. Three consecutive densitometry measurements were performed in each segment.

RESULTS

Those segments with reduced perfusion showed a significantly lower mean CT value on the enhanced scans (-813.4 +/- 57.1 Hounsfield units (HU) vs -794.0 +/- 44.8 HU, P = 0.01) and a significantly decreased contrast enhancement (12.3 +/- 18.2 HU vs 29.8 +/- 16.6 HU, P <0.01) when compared to segments with normal perfusion. Measurements from the unenhanced CT scans were not statistically different between segments with reduced and normal perfusion.

CONCLUSIONS

Spiral CT densitometry allows the assessment of at least segmental perfusion defects in patients with acute pulmonary embolism.

CD38: a NAADP degrading enzyme

The role of the multifunctional enzyme CD38 in formation of the Ca(2+)-mobilizing second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) was investigated. Gene silencing of CD38 did neither inhibit NAADP synthesis in intact Jurkat T cells nor in thymus or spleen obtained from CD38 knock out mice. In vitro, both NAADP formation by base-exchange and degradation to 2-phospho adenosine diphosphoribose were efficiently decreased. Thus in vivo CD38 appears to be a NAADP degrading rather than a NAADP forming enzyme, perhaps avoiding desensitizing NAADP levels in intact cells.

Modulation of Ca2+ entry and plasma membrane potential by human TRPM4b

TRPM4b is a Ca(2+)-activated, voltage-dependent monovalent cation channel that has been shown to act as a negative regulator of Ca(2+) entry and to be involved in the generation of oscillations of Ca(2+) influx in Jurkat T-lymphocytes. Transient overexpression of TRPM4b as an enhanced green fluorescence fusion protein in human embryonic kidney (HEK) cells resulted in its localization in the plasma membrane, as demonstrated by confocal fluorescence microscopy. The functionality and plasma membrane localization of overexpressed TRPM4b was confirmed by induction of Ca(2+)-dependent inward and outward currents in whole cell patch clamp recordings. HEK-293 cells stably overexpressing TRPM4b showed higher ionomycin-activated Ca(2+) influx than wild-type cells. In addition, analysis of the membrane potential using the potentiometric dye bis-(1,3-dibutylbarbituric acid)-trimethine oxonol and by current clamp experiments in the perforated patch configuration revealed a faster initial depolarization after activation of Ca(2+) entry with ionomycin. Furthermore, TRPM4b expression facilitated repolarization and thereby enhanced sustained Ca(2+) influx. In conclusion, in cells with a small negative membrane potential, such as HEK-293 cells, TRPM4b acts as a positive regulator of Ca(2+) entry.

Continuous monitoring of mixed venous oxygen saturation in infants after cardiac surgery

Continuous mixed venous oxygen saturation (SvO2c) was measured in 16 infants immediately after cardiac surgery. A polyurethane 4F, dual channel catheter (Opticath, Modell U440, Oximetrix) with fiberoptic filaments was introduced into the pulmonary artery during cardiothoracic surgery. The catheters were left in place for an average of 67.5 h (range 27 h -125 h) and there were no catheter-related complications. Correlation between continuous in vivo SvO2 values and in vitro values was satisfactory (r = 0.85), whereas a correlation between SvO2c and arterial oxygen saturation (SaO2) was not found (r = 0.07). The sampled arterial lactate values were inversely correlated to the simultaneously measured SvO2c, but the correlation coefficient was only r = -0.4. There was an inverse correlation between SvO2c and arteriovenous oxygen content difference (Ca-vDO2) (r = -0.82), and a marked inverse correlation to the calculated oxygen utilization ratio (r = -0.97). Therefore SvO2c continuously reflects the overall balance between oxygen consumption and delivery, but the use of SvO2 as a predictor of blood lactate levels is unreliable. A further purpose of the present study was to demonstrate the clinical applications and to show the usefulness of SvO2c-monitoring; particularly as a surveillance and early warning system, as a guide for assessing therapy and its relevance in interpreting other monitored parameters. In our opinion continuous SvO2 measurement is a reliable and valuable indicator of cardiopulmonary function in the immediate post-operative period, even in infants with complicated repair of cardiac malformations.

Chasing quantitative biases in neutron imaging with scintillator-camera detectors: a practical method with black body grids

We propose a method for improving the quantification of neutron imaging measurements with scintillator-camera based detectors by correcting for systematic biases introduced by scattered neutrons and other sources such as light reflections in the detector system. This method is fully experimental, using reference measurements with a grid of small black bodies (BB) to measure the bias contributions directly. Using two test samples, one made of lead alloy and having a moderate (20%) neutron transmission and one made of stainless-steel and having a very low (1%) transmission, we evaluated the improvement brought by this method in reducing both the average quantification bias and the uncertainty around this average bias after tomographic reconstruction. The results show that a reduction of the quantification bias of up to one order of magnitude can be obtained. For moderately transparent samples, little sensitivity is observed to the parameters used for the correction. For the more challenging sample with very low transmission, a correct placement of the BB grid is of utmost importance for a successful correction.

Thermodynamic studies of binary and ternary complexes of pig heart lactate dehydrogenase

The thermodynamics of the reaction catalyzed by pig heart muscle lactate dehydrogenase (LDH; EC1.1.1,27) have been studied in 0,2 M potassium phosphate buffer, pH 7, over the temperature range of 10 to 35 degrees C by using oxamate and oxalate to simulate the corresponding reactions of the substrates pyruvate and lactate, respectively. The various complexes formed are characterized by Gibbs free energies, enthalpies, and entropies. The Gibbs free energies were determined by equilibrium dialysis investigations, fluorescence titrations, and ultraviolet difference spectroscopy, while the reaction enthalpies stem from direct calorimetric measurements, Formulas are given for both the temperature dependence of the equilibrium constants and the variation with temperature of the enthalpies involved in the four reactions between LDH and NADH or NAD, LDH-NADH and oxamate, and LDH-NAD and oxalate. All reactions show a marked negative temperature coefficient, deltacp, of the binding enthalpies indicating partial refolding to be associated with binary and ternary complex formation. This interpretation appears very probable in view of recent x-ray crystallographic studies on lactate dehydrogenase from dogfish, which demonstrate a volume decrease to occur on binding of oxamate to the LDH-NADH complex. The validity of the thermodynamic parameters, as derived with substrate analogues, for the actual catalytic reaction, gains strong support from the agreement between the sum of the heats involved in the four intermediary reactions reported in this study and direct determinations of the overall enthalpy associated with the catalytic process published in the literature.

Nicotinic acid adenine dinucleotide phosphate (NAADP) degradation by alkaline phosphatase

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a ubiquitous second messenger providing a Ca(2+) trigger in a wide range of cell types. However, its metabolism is not well understood. Here, we demonstrate the presence of endogenous NAADP in HeLa cells. CD38, a promiscuous enzyme described to be involved in NAADP metabolism, was not detectable in HeLa cells. In cell-free extracts of HeLa cells, NAADP was degraded to nicotinic acid adenine dinucleotide (NAAD). The enzyme was enriched in membranes (10,000 × g pellet) and displayed characteristics typical of alkaline phosphatase (AP), e.g. pH optimum at 8-9 and sensitivity to the inhibitors L-homoarginine and L-leucine. Importantly, NAADP at physiological concentrations (50-100 nM) was degraded to NAAD. Expression of AP isoenzymes was analyzed in HeLa cells. Based on the results together with inhibitor studies, the placental AP isoform emerged as the best candidate for NAADP degradation in HeLa cells. In contrast to HeLa cells, Jurkat T cells or HEK293 cells did not express any AP isoenzymes and did not display any NAADP 2'-phosphatase activity. Finally, the placental AP isoform was expressed heterologously in HEK293 cells, resulting in reconstitution of NAADP 2'-phosphatase activity in cell-free extracts. On the basis of the results, we provide evidence for AP as the metabolizing enzyme of NAADP in cells that do not express CD38.

Mature T-cell lymphomagenesis induced by retroviral insertional activation of Janus kinase 1

Retroviral vectors (RVs) are powerful tools in clinical gene therapy. However, stable genomic integration of RVs can be oncogenic, as reported in several animal models and in clinical trials. Previously, we observed that T-cell receptor (TCR) polyclonal mature T cells are resistant to transformation after gammaretroviral transfer of (proto-)oncogenes, whereas TCR-oligoclonal T cells were transformable in the same setting. Here, we describe the induction of a mature T-cell lymphoma (MTCL) in TCR-oligoclonal OT-I transgenic T cells, transduced with an enhanced green fluorescent protein (EGFP)-encoding gammaretroviral vector. The tumor cells were of a mature T-cell phenotype and serially transplantable. Integration site analysis revealed a proviral hit in Janus kinase 1 (Jak1), which resulted in Jak1 overexpression and Jak/STAT-pathway activation, particularly via signal transducer and activator of transcription 3 (STAT3). Specific inhibition of Jak1 markedly delayed tumor growth. A systematic meta-analysis of available gene expression data on human mature T-cell lymphomas/leukemias confirmed the relevance of Jak/STAT overexpression in sporadic human T-cell tumorigenesis. To our knowledge, this is the first study to describe RV-associated insertional mutagenesis in mature T cells.

"Staircase" glucose stimulation of insulin secretion in obesity. Measure of beta-cell sensitivity and capacity

A special glucose infusion test was used to provide successive steplike increments of glucose stimulation in six normal-weight and seven obese subjects. This “staircase” method of glucose infusion demonstrates that insulin responds in “spike” fashion despite maintenance of a continuous, fixed, submaximal glucose stimulation. Further, the “spike” response recurs as the glucose concentration is stepped up.

Obese subjects showed an exaggeration of both the first phase “spike” pattern and the more gradual second phase of insulin release. Mathematical analysis of early phase insulin release indicates that obese persons have greater total amounts of insulin available for release at all glucose concentrations than do normals, yet the proportion of totally available insulin released to a given glucose stimulus is not increased in obesity.

These findings imply that the early phase, hyperinsulin response to glucose in obesity is due to a greater quantity of insulin available for release rather than to an increased sensitivity of the beta cell to glucose.

Wetting of a symmetrical binary fluid mixture on a wall

We study the wetting behavior of a symmetrical binary fluid below the demixing temperature at a nonselective attractive wall. Although it demixes in the bulk, a sufficiently thin liquid film remains mixed. On approaching liquid vapor coexistence, however, the thickness of the liquid film increases and it may demix and then wet the substrate. We show that the wetting properties are determined by an interplay of the two length scales related to the density and the composition fluctuations. The problem is analyzed within the framework of a generic two component Ginzburg-Landau functional (appropriate for systems with short-ranged interactions). This functional is minimized both numerically and analytically within a piecewise parabolic potential approximation. A number of surface transitions are found, including first-order demixing and prewetting, continuous demixing, a tricritical point connecting the two regimes, or a critical end point beyond which the prewetting line separates a strongly and a weakly demixed film. Our results are supported by detailed Monte Carlo simulations of a symmetrical binary Lennard-Jones fluid at an attractive wall.