Specific probiotic strains and their combinations counteract adhesion of Enterobacter sakazakii to intestinal mucus

Enterobacter sakazakii is an opportunistic pathogen and an occasional contaminant in powdered infant formula. Interaction between specific probiotics and E. sakazakii may reduce the risk of infection. The aim of this study was to characterize in vitro the ability of probiotics (alone and in combinations) to inhibit, compete with and displace the adhesion of E. sakazakii to immobilized human mucus and to assess their capacity to aggregate with pathogen. Specific probiotic strains have proved to aggregate E. sakazakii cells and, through competitive exclusion, inhibition and displacement of the adhered pathogen, were able to inhibit E. sakazakii action on intestinal mucus. The ability to inhibit and to displace adhered pathogen depended on both the probiotic and the pathogen, suggesting that several complementary mechanisms are involved in the processes. We suggest that the selection of specific probiotic strains and their combinations may be a useful means of counteracting E. sakazakii contamination in infant formula and thus to reduce the risk of emerging infection. This approach may also allow the development of new probiotic combinations to counteract the risks associated with other pathogens by improving the intestinal barrier against pathogens.     

DNA-induced alpha-helical structure in the NH2-terminal domain of histone H1

It is important to establish the structural properties of linker histones to understand the role they play in chromatin higher order structure and gene regulation. Here, we use CD, NMR, and IR spectroscopy to study the conformation of the amino-terminal domain of histone H1 degrees, free in solution and bound to the DNA. The NH(2)-terminal domain has little structure in aqueous solution, but it acquires a substantial amount of alpha-helical structure in the presence of trifluoroethanol (TFE). As in other H1 subtypes, the basic residues of the NH(2)-terminal domain of histone H1 degrees are clustered in its COOH-terminal half. According to the NMR results, the helical region comprises the basic cluster (Lys(11)-Lys(20)) and extends until Asp(23). The fractional helicity of this region in 90% TFE is about 50%. His(24) together with Pro(25) constitute the joint between the NH(2)-terminal helix and helix I of the globular domain. Infrared spectroscopy shows that interaction with the DNA induces an amount of alpha-helical structure equivalent to that observed in TFE. As coulombic interactions are involved in complex formation, it is highly likely in the complexes with DNA that the minimal region with alpha-helical structure is that containing the basic cluster. In chromatin, the high positive charge density of the inducible NH(2)-terminal helical element may contribute to the binding stability of the globular domain.     

End-Product Diacylglycerol Enhances the Activity of PI-PLC through Changes in Membrane Domain Structure

Diacylglycerol (DAG)-induced activation of phosphatidylinositol-phospholipase C (PI-PLC) was studied with vesicles containing PI, either pure or in mixtures with dimyristoyl phosphatidylcholine, distearoyl phosphatidylcholine, sphingomyelin, or galactosylceramide, used as substrates. At 22°C, DAG at 33 mol % increased PI-PLC activity in all of the mixtures, but not in pure PI bilayers. DAG also caused an overall decrease in diphenylhexatriene fluorescence polarization (decreased molecular order) in all samples, and increased overall enzyme binding. Confocal fluorescence microscopy of giant unilamellar vesicles of all of the compositions under study, with or without DAG, and quantitative evaluation of the phase behavior using Laurdan generalized polarization, and of enzyme binding to the various domains, indicated that DAG activates PI-PLC whenever it can generate fluid domains to which the enzyme can bind with high affinity. In the specific case of PI/dimyristoyl phosphatidylcholine bilayers at 22°C, DAG induced/increased enzyme binding and activation, but no microscopic domain separation was observed. The presence of DAG-generated nanodomains, or of DAG-induced lipid packing defects, is proposed instead for this system. In PI/galactosylceramide mixtures, DAG may exert its activation role through the generation of small vesicles, which PI-PLC is known to degrade at higher rates. In general, our results indicate that global measurements obtained using fluorescent probes in vesicle suspensions in a cuvette are not sufficient to elucidate DAG effects that take place at the domain level. The above data reinforce the idea that DAG functions as an important physical agent in regulating membrane and cell properties.     

Effect of boron on soluble protein and sugar contents of tomato roots

Summary In relation to a biochemical diagnosis of B-affected plants, the influence of boron on soluble protein and sugar contents in roots of tomato plants was investigated. Differences in protein and sugar contents occur throughout the culture period of tomato plant. Boron deficiency results in an accumulation of proteins and both total and reducing sugars.     

Membrane Permeabilization Induced by Sphingosine: Effect of Negatively Charged Lipids

Sphingosine [(2S, 3R, 4E)-2-amino-4-octadecen-1, 3-diol] is the most common sphingoid long chain base in sphingolipids. It is the precursor of important cell signaling molecules, such as ceramides. In the last decade it has been shown to act itself as a potent metabolic signaling molecule, by activating a number of protein kinases. Moreover, sphingosine has been found to permeabilize phospholipid bilayers, giving rise to vesicle leakage. The present contribution intends to analyze the mechanism by which this bioactive lipid induces vesicle contents release, and the effect of negatively charged bilayers in the release process. Fluorescence lifetime measurements and confocal fluorescence microscopy have been applied to observe the mechanism of sphingosine efflux from large and giant unilamellar vesicles; a graded-release efflux has been detected. Additionally, stopped-flow measurements have shown that the rate of vesicle permeabilization increases with sphingosine concentration. Because at the physiological pH sphingosine has a net positive charge, its interaction with negatively charged phospholipids (e.g., bilayers containing phosphatidic acid together with sphingomyelins, phosphatidylethanolamine, and cholesterol) gives rise to a release of vesicular contents, faster than with electrically neutral bilayers. Furthermore, phosphorous 31-NMR and x-ray data show the capacity of sphingosine to facilitate the formation of nonbilayer (cubic phase) intermediates in negatively charged membranes. The data might explain the pathogenesis of Niemann-Pick type C1 disease.     

Postnatal cell proliferation and death in a lateralized,gender‐related,asymmetric nucleus

Sexual differentiation and lateralization of neurone number in a discrete forebrain nucleus (SDApc) related to masculine vocal emission, occur contemporaneously in postnatal (P0–P15) gerbils. Stereological estimates of cell proliferation and death during SDApc organization were made by BrdU labelling and pyknosis, respectively. Results confirmed that rates of apoptosis were greater in females and lateralized in males. Immunoreactive BrdU cells, located in the SDApc at P0–P6, with low levels at P15, were not numerically different between the sexes. Only at one age, P0, in males, was a left‐right difference seen in BrdU‐immunoreactive cell numbers. Microglia, identified by isolectin immunostaining, were numerically similar to BrdU cells. We suggest that apoptosis, rather than neurogenesis, differentiates and lateralizes SDApc organization, and proliferating cells are microglia, phagocytosing debris. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 150–158, 2001     

The freshwater Copepoda (Crustacea) of Costa Rica with notes on some species

Sixteen species of Copepoda were recorded in this first detailed study of Costa Rican zooplankton. Two of these species are halophile. Notes are given on some of the species and their distribution. One new species found will be described elsewhere. The Costa Rican fauna resembles in composition the fauna of other Central American and Caribbean regions. Relatively few species were recorded. This is partly due to a low intensity of sampling but also to the paucity of lentic habitats. The occurrence of two circumtropical species of Mesocyclops is interesting.

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Résumé 16 espèces de Copépodes ont été inventoriées au cours d'une première étude détaillée du zooplankton dulcaquicole de Costa Rica. Deux des espèces trouvées sont halophiles. Des remarques sont faites a propos de quelques espèces et de leur répartition. Une nouvelle espèce est nouvelle — elle sera décrite par ailleurs. La fauna de Costa Rica ressemble par sa composition à celle des autres pays d'Amérique centrale et des îles caraibes. Relativement peu d'espèces sont notées. La faible intensité de l'échantillonnage mais aussi la pauvreté en habitats limniques en sont responsables. La présence de deux espèces circumtropicales de Mesocyclops est intéressante.

     

Different effects of long- and short-chain ceramides on the gel-fluid and lamellar-hexagonal transitions of phospholipids: a calorimetric, NMR, and x-ray diffraction study

The effects on dielaidoylphosphatidylethanolamine (DEPE) bilayers of ceramides containing different N-acyl chains have been studied by differential scanning calorimetry small angle x-ray diffraction and (31)P-NMR spectroscopy. N-palmitoyl (Cer16), N-hexanoyl (Cer6), and N-acetyl (Cer2) sphingosines have been used. Both the gel-fluid and the lamellar-inverted hexagonal transitions of DEPE have been examined in the presence of the various ceramides in the 0-25 mol % concentration range. Pure hydrated ceramides exhibit cooperative endothermic order-disorder transitions at 93 degrees C (Cer16), 60 degrees C (Cer6), and 54 degrees C (Cer2). In DEPE bilayers, Cer16 does not mix with the phospholipid in the gel phase, giving rise to high-melting ceramide-rich domains. Cer16 favors the lamellar-hexagonal transition of DEPE, decreasing the transition temperature. Cer2, on the other hand, is soluble in the gel phase of DEPE, decreasing the gel-fluid and increasing the lamellar-hexagonal transition temperatures, thus effectively stabilizing the lamellar fluid phase. In addition, Cer2 was peculiar in that no equilibrium could be reached for the Cer2-DEPE mixture above 60 degrees C, the lamellar-hexagonal transition shifting with time to temperatures beyond the instrumental range. The properties of Cer6 are intermediate between those of the other two, this ceramide decreasing both the gel-fluid and lamellar-hexagonal transition temperatures. Temperature-composition diagrams have been constructed for the mixtures of DEPE with each of the three ceramides. The different behavior of the long- and short-chain ceramides can be rationalized in terms of their different molecular geometries, Cer16 favoring negative curvature in the monolayers, thus inverted phases, and the opposite being true of the micelle-forming Cer2. These differences may be at the origin of the different physiological effects that are sometimes observed for the long- and short-chain ceramides.