Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field

A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modeled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kilohertz range and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied alternating current electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys J 95:L19–L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of microliter samples is discussed.     

Convergent adaptation of Saccharomyces uvarum to sulfite,an antimicrobial preservative widely used in human-driven fermentations

Different species can find convergent solutions to adapt their genome to the same evolutionary constraints, although functional convergence promoted by chromosomal rearrangements in different species has not previously been found. In this work, we discovered that two domesticated yeast species, Saccharomyces cerevisiae, and Saccharomyces uvarum, acquired chromosomal rearrangements to convergently adapt to the presence of sulfite in fermentation environments. We found two new heterologous chromosomal translocations in fermentative strains of S. uvarum at the SSU1 locus, involved in sulfite resistance, an antimicrobial additive widely used in food production. These are convergent events that share similarities with other SSU1 locus chromosomal translocations previously described in domesticated S. cerevisiae strains. In S. uvarum, the newly described VII^XVI and XI^XVI chromosomal translocations generate an overexpression of the SSU1 gene and confer increased sulfite resistance. This study highlights the relevance of chromosomal rearrangements to promote the adaptation of yeast to anthropic environments.     

Influence of the interactions among ecological variables in the characterization of zearalenone producing isolates of Fusarium spp

To carry out the physiological characterization of Fusarium graminearum and F. culmorum isolates with regard to its zearalenone producing ability, an in-depth experiment with a full factorial design was conducted. The effects and mutual interactions of temperature, moisture, substrate and isolate on the production of the toxin were studied. The study was done with twelve isolates of Fusarium (7 of F. graminearum and 5 of F. culmorum). The analysis of variance shows that there is a complex interaction of all of these factors, which can influence the relative concentrations of the mycotoxin produced, and hence, the correct physiological characterization of the strain. All the tested cultures were susceptible to invasion by Fusarium. The moisture content of grains (water activity values 0.960, 0.970 and 0.980) did not constitute a limiting factor for fungal growth or ZEA production, but incubation temperature (15 degrees C, 20 degrees C, 28 degrees C, and 32 degrees C) affected the rate of zearalenone synthesis. Very low or undetectable ZEA production was observed at 32 degrees C. All tested isolates showed a characteristic behavior concerning the optimum temperature for ZEA production, which was usually 20 degrees C maintained during the whole incubation period. This finding, which does not agree with other reports obtained with strains from different origins, suggests that there are genetic differences that would explain the particular physiological behavior of each isolate related to the optimal production conditions for ZEA. The existence of significant differences regarding the susceptibility of the assayed cereal grains (wheat, corn and rice) used for ZEA production by the different Fusarium species (F. graminearum and F. culmorum) is described for the first time in this paper.     

New pinch-porphyrin complexes with quantum mixed spin ground state S=3/2,5/2 of iron (III) and their catalytic activity as peroxidase

New complexes of the pinch-porphyrin family were obtained from the dimethylester of (proto-, meso-, and deutero-porphyrinato)iron(III) with the ligand [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine] 1-3 and with the ligand [N-pyridin-2-ylmethyl-N'-[3-[(pyridin-2-ylmethyl)-amino]-propyl]-propane-1,3-diamine] 4-6. The UV/VIS studies of 1-6 indicate an increase in the distortion of the ligand field excited state. The 1H NMR spectra of 1-6 at RT and over the range 223-328 K show iron(III)-complexes with quantum mixed spin state (qms) S=5/2, S=3/2. The chemical shifts of the meso protons are consistent with qms state S=3/2, S=5/2, where the S=3/2 spin state is lowest in energy. For methyl-heme the chemical shifts are also consistent with a qms state but now the S=5/2 ground state is lowest in energy. ESR spectra of 1-6 show two different species, B and C, of iron(III) with qms, S=5/2, S=3/2 consistent with the 1H NMR results. Species B with 70% of S=5/2 and species C with 72.5% of S=3/2. The catalytic activity as peroxidase of 1-6 was quantified by guaiacol test; their theoretical maximum rate constants were k(cat) approximately 10(2)-10(3) M(-1) s(-1). A quantitative empirical correlation is found: the higher the 32 spin contribution to the qms state and the higher proportion of this species into the samples, the higher the peroxidase activity. Such a correlation was also obtained for pinch-porphyrins already reported.     

Monitoring dynamic expression of nuclear genes in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> by using a synthetic luciferase reporter gene

For monitoring the expression profile of selected nuclear genes in Chlamydomonas reinhardtii in response to altered environmental parameters or during cell cycle, in the past many RNA or protein samples had to be taken and analyzed by RNA hybridization or protein immunoblotting. Here we report the synthesis of a gene that codes for the luciferase of Renilla reniformis (RLuc) and is adapted to the nuclear codon usage of C. reinhardtii. This crluc gene was expressed alone or as a fusion to the zeocin resistance gene ble under control of different promoter variants. Luciferase activity was monitored in living cells, increased with the promoter strength and paralleled the amount of expressed protein. Under control of the Lhcb-1 promoter the Luc-activity in synchronized cultures was dependent on the dark-light cycle. Additionally, crluc was placed under control of the Chop-2 promoter and activity was measured under different light conditions. Chop-2 promoter activity was found to be most pronouced under low-light and dark conditions, further supporting that channelrhodopsin-2 is most active in dark-adapted cells. We conclude that crluc is a reliable tool for convenient monitoring of nuclear gene expression in C. reinhardtii.     

Fat absorptive processes in the intestine of the Antarctic fish Notothenia coriiceps (Richardson, 1844)

Absorption of lipids by the enterocytes of Notothenia coriiceps, an omnivorous Antarctic and subAntarctic fish, was studied by light and electron microscopy. The lipids are absorbed by the anterior and middle intestine segments. They appear as fat droplets that measure from 0.5 to 7 μm of diameter and which accumulate in the apical cytoplasm within the first 24 h and seem to be the main fat storage form in the enterocytes. Fat is also observed as lipid particles with 60–300 nm inside the rough endoplasmic reticulum and cytoplasmic smooth vesicles. The epithelial intercellular space and the mucosal inner lamina contain lipid particles, which probably are the fat transport form. Our observations show that an intense lipid absorptive process takes place in N. coriiceps digestive system, due to the great extension of the intestine involved and due to the great lipid accumulation found in the epithelial compartment.     

Formaldehyde cross-linking of gliadin films: effects on mechanical and water barrier properties

In this study, pioneering results on specific chemical modifications of wheat gluten gliadins and the corresponding impact on mechanical and water barrier properties of derived films are presented. Films were prepared from gliadins chemically treated with formaldehyde and subsequently mixed with different concentrations of glycerol as a plasticizing agent. Water vapor barrier and mechanical properties of the films were evaluated as a function of relative humidity and glycerol concentration. Formaldehyde treatment led to enhanced mechanical properties and, to a lesser extent, improved water barrier of the films, effects which point to the formation of new intermolecular bonds between monomeric gliadins. The occurrence of cross-linking was supported by SDS-PAGE analysis. Cross-linked films maintained their integrity after immersion in water and had similar optical properties to control films. The effect of glycerol and humidity on water vapor permeability and the mechanical properties of films was less acute when proteins were treated with formaldehyde. Thus, chemical treatment of proteins is shown to be a very effective route for optimizing the use of these films in packaging applications.