Water and glucose gradients in the substrate measured with NMR imaging during solid-state fermentation with Aspergillus oryzae

Gradients inside substrate particles cannot be prevented in solid-state fermentation. These gradients can have a strong effect on the physiology of the microorganisms but have hitherto received little attention in experimental studies. We report gradients in moisture and glucose content during cultivation of Aspergillus oryzae on membrane-covered wheat-dough slices that were calculated from (1)H-NMR images. We found that moisture gradients in the solid substrate remain small when evaporation is minimized. This is corroborated by predictions of a diffusion model. In contrast, strong glucose gradients developed. Glucose concentrations just below the fungal mat remained low due to high glucose uptake rates, but deeper in the matrix glucose accumulated to very high levels. Integration of the glucose profile gave an average concentration close to the measured average content. On the basis of published data, we expect that the glucose levels in the matrix cause a strong decrease in water activity. The results demonstrate that NMR can play an important role in quantitative analysis of water and glucose gradients at the particle level during solid-state fermentation, which is needed to improve our understanding of the response of fungi to this nonconventional fermentation environment.     

Characterization of Phospholipid Mixed Micelles by Translational Diffusion

The concentration dependence of the translational self diffusion rate, D (s), has been measured for a range of micelle and mixed micelle systems. Use of bipolar gradient pulse pairs in the longitudinal eddy current delay experiment minimizes NOE attenuation and is found critical for optimizing sensitivity of the translational diffusion measurement of macromolecules and aggregates. For low volume fractions Phi (Phi\\ le 15% v/v) of the micelles, experimental measurement of the concentration dependence, combined with use of the D (s)= D (o)(1-3.2lambdaPhi) relationship, yields the hydrodynamic volume. For proteins, the hydrodynamic volume, derived from D (s) at infinitely dilute concentration, is found to be about 2.6 times the unhydrated molecular volume. Using the data collected for hen egg white lysozyme as a reference, diffusion data for dihexanoyl phosphatidylcholine (DHPC) micelles indicate approximately 27 molecules per micelle, and a critical micelle concentration of 14 mM. Differences in translational diffusion rates for detergent and long chain phospholipids in mixed micelles are attributed to rapid exchange between free and micelle-bound detergent. This difference permits determination of the free detergent concentration, which, for a high detergent to long chain phospholipid molar ratio, is found to depend strongly on this ratio. The hydrodynamic volume of DHPC/POPC bicelles, loaded with an M2 channel peptide homolog, derived from translational diffusion, predicts a rotational correlation time that slightly exceeds the value obtained from peptide (15)N relaxation data.     

Phytoremediation of MTBE with hybrid poplar trees

This research investigates the fate and transport of methyl tert-butyl ether (MTBE) in phytoremediation, particularly the uptake and volatilization of MTBE in lab-scale hydroponic systems. The research reveals that MTBE was taken up by hybrid poplar cuttings and volatilized to the atmosphere. Volatilization of MTBE occurred through both stems and leaves. The concentration of MTBE in the transpiration stream declined exponentially with height, indicating that the uptake and volatilization along the stems are an important removal mechanism of MTBE in phytoremediation. Volatilization, via diffusion from the stems, has not been directly measured previously. No volatile MTBE metabolites were detected; however, mass balance closure and metabolite detection were not primary objectives of this study. The greatest amount of MTBE in plant biomass was associated with the woody stems from the previous year's growth, owing in part to the large biomass of stems. MTBE in the plant tissues appears to reach a steady state concentration and there does not appear to be an accumulation process that could lead to highly elevated concentrations relative to the groundwater source.     

Power line frequency electromagnetic fields do not increase the rate of protein synthesis in human skin fibroblasts as previously reported

Rodemann et al. [Rodemann et al. (1987): Biochem Biophys Res Commun 145:1-9] reported that human skin fibroblasts increase their rate of protein synthesis by as much as over ninefold in response to long term exposure to 20 Hz, 8.4 mT (84 G) magnetic fields. Here we report studies of protein synthesis using an identical cell type, exposure conditions, and the same means of measuring protein synthetic rates. Our initial goal was to determine if the earlier results could be replicated, but we found an inconsistency in the earlier protocol. It exposed cells to [(3)H]leucine for 6 h prior to measuring incorporation into protein. We found, however, that 24 h is required for [(3)H]leucine to reach a steady state distribution across the cells' plasma membranes. In addition, we typically measured 100-200 cpm/thousand cells. This is four- to eightfold higher than the 19-28 cpm/1000 cells previously reported. Using these conditions, we could find no significant difference in protein synthesis rates between control cells and cells exposed for up to three weeks in an identical electromagnetic field. In addition, we investigated the effects of a 60 Hz field since that is the frequency used for electric power distribution in the United States. Again, we could find no significant effect of this field on rates of protein synthesis, even after 21 days of exposure.     

The degree of macromolecular crowding in the cytoplasm and nucleoplasm of mammalian cells is conserved

Macromolecular crowding provides the cytoplasm and the nucleoplasm with strongly viscoelastic properties and renders the diffusion of soluble proteins in both fluids anomalous. Here, we have determined the nanoscale viscoelasticity of the cytoplasm and the nucleoplasm in different mammalian cell lines. In contrast to the cell-specific response on the macroscale the nanoscale viscoelasticity (i.e. the behavior on length scales about 100-fold smaller than the cell size) only showed minor variations between different cell types. Similarly, the associated anomalous diffusion properties varied only slightly. Our results indicate a conserved state of macromolecular crowding in both compartments for a variety of mammalian cells with the cytoplasm being somewhat more crowded than the nucleus.     

Membrane entrapped Saccharomyces cerevisiae in a biosensor-like device as a generic rapid method to study cellular metabolism

We describe a new, faster and convenient method to study some metabolic characteristics - by the successful application of immobilized yeast cells (S. cerevisiae) in a microbial biosensor-like device. Microbial biosensors consist of microorganisms immobilized on the surface of a membrane or in a gel, in close contact with a transducer. Almost all works published to date have used biosensors for analyses in which a concentration-related property of the external medium is measured. A different approach is presented here; we have successfully used S. cerevisiae and a carbon dioxide electrode as the main components of a biosensor-like device, used as a proof of concept, for a system useful to characterize metabolic parameters of the microbial cells immobilized on a carbon dioxide electrode. The biosensor-like device we are presenting allows us to calculate Michaelis-Menten parameters related to the kinetics of transport and degradation of several carbohydrates (i.e., glucose, fructose, galactose, sucrose and xylose, with K(m(app)) of 6.0, 5.8, 0.9, 2.0, and 147 mM, respectively), and the study of the kinetics of expression of non-constitutive proteins related to the transport and degradation of galactose.     

K‐Birnessite Electrode Obtained by Ion Exchange for Potassium‐Ion Batteries: Insight into the Concerted Ionic Diffusion and K Storage Mechanism

Novel and low‐cost rechargeable batteries are of considerable interest for application in large‐scale energy storage systems. In this context, K‐Birnessite is synthesized using a facile solid‐state reaction as a promising cathode for potassium‐ion batteries. During synthesis, an ion exchange protocol is applied to increase K content in the K‐Birnessite electrode, which results in a reversible capacity as high as 125 mAh g^?1 at 0.2 C. Upon K⁺ exchange the reversible phase transitions are verified by in situ X‐ray diffraction (XRD) characterization. The underlying mechanism is further revealed to be the concerted K⁺ ion diffusion with quite low activation energies by first‐principle simulations. These new findings provide new insights into electrode process kinetics, and lay a solid foundation for material design and optimization of potassium‐ion batteries for large‐scale energy storage.     

Ancestral alleles and population origins: inferences depend on mutation rate.

Previous studies have found that at most human loci, ancestral alleles are "African," in the sense that they reach their highest frequency there. Conventional wisdom holds that this reflects a recent African origin of modern humans. This paper challenges that view by showing that the empirical pattern (of elevated allele frequencies within Africa) is not as pervasive as has been thought. We confirm this African bias in a set of mainly protein-coding loci, but find a smaller bias in Alu insertion polymorphisms, and an even smaller bias in noncoding loci. Thus, the strong bias that was originally observed must reflect some factor that varies among data sets--something other than population history. This factor may be the per-locus mutation rate: the African bias is most pronounced in loci where this rate is high. The distribution of ancestral alleles among populations has been studied using 2 methods. One of these involves comparing the fractions of loci that reach maximal frequency in each population. The other compares the average frequencies of ancestral alleles. The first of these methods reflects history in a manner that depends on the mutation rate. When that rate is high, ancestral alleles at most loci reach their highest frequency in the ancestral population. When that rate is low, the reverse is true. The other method--comparing averages--is unresponsive. Average ancestral allele frequencies are affected neither by mutation rate nor by the history of population size and migration. In the absence of selection and ascertainment bias, they should be the same everywhere. This is true of one data set, but not of 2 others. This also suggests the action of some factor, such as selection or ascertainment bias, that varies among data sets.