Comparison of the serum selenium content of healthy adults living in the Antwerp region (Belgium) with recent literature data.

Graphite furnace atomic absorption spectrometry, after improved matrix modification and using Zeeman background correction, was used to measure the serum selenium content of healthy adults living in the Antwerp region (Belgium). The mean serum concentration of 13 men and 13 women, sampled once a month during 1 year, was 84.3 +/- 9.4ng/ml with a broad range of 51.4-121.7 ng/ml. The intra-individual variation was remarkably high. Recent literature on selenium concentrations is reviewed and values are tabulated, with limitation to healthy adults and European countries. The mean serum selenium concentration measured corresponded well to older literature data for Belgium. The obtained values were found to be in the medium range compared with the literature data for other European countries.     

Interactions between membranes and cytolytic peptides

The physico-chemical and biological properties of cytolytic peptides derived from diverse living entities have been discussed. The principal sources of these agents are bacteria, higher fungi, cnidarians (coelenterates) and the venoms of snakes, insects and other arthropods. Attention has been directed to instances in which cytolytic peptides obtained from phylogenetically remote as well as from related sources show similarities in nature and/or mode of action (congeneric lysins). The manner in which cytolytic peptides interact with plasma membranes of eukaryotic cells, particularly the membranes of erythrocytes, has been discussed with emphasis on melittin, thiolactivated lysins and staphylococcal alpha-toxin. These and other lytic peptides are characterized in Table III. They can be broadly categorized into: (a) those which alter permeability to allow passage of ions, this process eventuating in colloid osmotic lysis, signs of which are a pre-lytic induction or latent period, pre-lytic leakage of potassium ions, cell swelling and inhibition of lysis by sucrose. Examples of lysins in which this mechanism is involved are staphylococcal alpha-toxin, streptolysin S and aerolysin; (b) phospholipases causing enzymic degradation of bilayer phospholipids as exemplified by phospholipases C of Cl. perfringens and certain other bacteria; (c) channel-forming agents such as helianthin, gramicidin and (probably) staphylococcal delta-toxin in which toxin molecules are thought to embed themselves in the membrane to form oligomeric transmembrane channels.     

Formation and properties of cell-size lipid bilayer vesicles

Hydration of single or mixed phospholipids or lipid protein mixtures at low ionic strength results in the formation of a population of large, solvent free, single bilayer vesicles with included volumes of up to 300 microliters/mumol lipid. Their size ranges from 0.1 to 300 microns and they can be sorted out according to size by centrifugation. When formed in distilled water their internal solution has a conductivity of 20-50 microseconds/cm-1, an osmolarity of 0.5-5 mOsM, and a density of 1.0005-1.001. The osmotic pressure produced by the internal solutes cause a surface stress of 25 dyn/cm for a 20-microns vesicle. Their elastic constant ranges from 75-150 dyn/cm. During formation they can internalize particles such as latex beads or cell nuclei. They can be impaled with microelectrodes, or patch clamped. They can also be sealed to a small Vaseline-treated hole in a thin partition between two aqueous compartments. Sealing occurs in two stages. In the first stage sealing resistance is similar to that seen with patch-clamp pipettes. In the second stage, a much tighter seal is obtained. After sealing, the smaller portion of the sealed vesicle can be selectively broken by an electric shock leaving a single membrane across the hole. The capacitance and resistance of such membranes, in the presence of 10 mM NaCl, are approximately 0.7 microF/cm2 and 10(8) omega cm2 for pure lipid vesicles. Gramicidin increases the membrane conductance and monazomycin induces voltage-dependent gating thus providing further evidence that the vesicles are bounded by a single bilayer.     

Formation of poly(hydroxybutyrate-co-hydroxyvalerate) by Azotobacter vinelandii UWD.

Azotobacter vinelandii UWD formed polyhydroxyalkanoate (PHA) copolymers containing beta-hydroxybutyrate and beta-hydroxyvalerate (HV) when grown in a medium containing glucose as the primary C source and valerate (pentanoate) as a precursor. Copolymer was not formed when propionate was added to the glucose medium but was formed when heptanoate, nonanoate, or trans-2-pentenoate was present. Optimal levels of HV were formed when valerate was added at the time of maximum PHA synthesis, although HV incorporation was not dependent on glucose catabolism. HV content in the polymer was increased from 17 to 24 mol% by adding 10 to 40 mM valerate to glucose medium, but HV insertion into the polymer occurred at a fixed rate. Similarly, the addition of valerate to a fed-batch culture of strain UWD in beet molasses in a fermentor produced 19 to 22 g of polymer per liter, containing 8.5 to 23 mol% HV after 38 to 40 h. The synthesis of HV in these cultures also occurred at a fixed rate (2.3 to 2.8 mol% h-1), while the maximum PHA production rate was 1.1 g liter-1 h-1. During synthesis of copolymer in batch or fed-batch culture, the yield from conversion of glucose into PHA (YP/S) remained at maximum theoretical efficiency (greater than or equal to 0.33 g of PHA per g of glucose consumed). Up to 45 mol% C source, but the PHA produced amounted to less than 1 g/liter. The combination of 30 mM valerate as a sole C source and 0.5 mM 4-pentenoate increased the HV content in the polymer to 52 mol%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phenotypic Diversity and Patterns of Variation in West and Central African Plantains (Musa Spp., AAB group Musaceae)

Plantains (Musa spp., AAB group) are an important food crop and an integral component of the farming systems in the lowland humid forest zone of West and Central Africa. A group of 24 plantain cultivars, representing the major variability in West Africa, was evaluated for nine quantitative characters. The association between growth and yield parameters in this African plantain germplasm was examined to determine if the pattern of quantitative variation in inflorescence and vegetative traits agreed with taxonomic groupings based on inflorescence type and plant size. Phenotypic correlations between these traits were calculated. Giant cultivars were taller, their pseudostem thicker, and they flowered much later than medium-sized cultivars. Giant cultivars produced more foliage, resulting in heavier bunches with more hands and fruits. Groupings that resulted following principal component analysis (PCA) supported conventional taxonomic groupings of plantains. PC A was based mainly on time to flowering, pseudostem height, and number of fruits. The last two traits, in combination with the number of hermaphrodite flowers and the persistence of the male bud, sufficed to group plantain cultivars.     

Fledgling production of EidersSomateria mollissima in The Netherlands

Summary For 28 years, the survival up to fledging of Eider ducklings has been determined in the Dutch colony on Vlieland. On average 0.342 (0.001–1.528) ducklings per female fledged yearly. Within the ranges observed, the total number of ducklings that fledged seemed to be independent of the number of breeding females (range 800–2700) and the number of Herring Gulls in the study period. Indications were found of a sex-linked mortality occurring in some years. Correlations with a number of environmental factors suggested that low temperature in winter, high temperature at the end of May and the beginning of June, calm weather in May and June, and a high number of Herring Gulls were profitable for fledgling success. However, a stepwise multiple regression indicated only the temperature at the beginning of June as significant, explaining about 18 % of the total variance. The absence of a negative relation with breeding gull numbers confirms the interpretation of the role of the Herring Gull as a secondary mortality factor. Experiments showed that Goose Virus Hepatitis (syn. Goose Influenza or Goose Pest) was a primary cause of mortality among ducklings older than one week. The effect of diseases in the field was difficult to establish as diseased and weakened ducklings were usually eaten by gulls. A long-lasting fledgling failure was recorded from 1966 up to and including 1977. In the same period changes were noted in the biological systems in the North Sea.

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Zusammenfassung In einer Eiderenten-Kolonie auf der holländischen Insel Vlieland wurden die Überlebensraten der Küken 28 Jahre lang erfaßt. Im Mittel wurden jährlich 0.342 (0.001–1.528) Küken pro Weibchen flügge. Die Gesamtzahl der Küken war offensichtlich von der Anzahl brütender Weibchen (800–2700) sowie der Anzahl der Silbermöwen unabhängig. In einigen Jahren gab es Anzeichen für eine geschlechtsabhängige Sterblichkeit. Beziehungen zwischen der Rate flügger Jungvögel und einigen Umweltparametern, wie niedriger Temperatur im Winter, hoher Temperatur Ende Mai bis Anfang Juni, windarmes Wetter im Mai und Juni sowie der Präsenz vieler Silbermöwen ließen sich aufzeigen. Eine stufenweise multiple Regression zeigte jedoch, daß nur die Temperatur Anfang Juni einen signifikanten Einfluß hatte. Das Fehlen einer negativen Korrelation mit der Anzahl brütendee Möwen stützt die Annahme, daß die Rolle dere Silbermöwe als zweitrangig einzustufen ist. Versuche belegten, daß der Virus der Gänsehepatitis die Sterblichkeit von mindestens eine Woche alten Kücken unmittelbar bestimmte. Der Einfluß von Krankheiten konnte im Feld nur bedingt festgestellt werden, weil Möwen kranke und geschwächte Kücken üblicherweise fressen. Ein anhaltender Tiefstand des Aufzuchterfolges von 1966 bis 1977 fiel zeitlich mit allgemeinen Veränderungen der biologischen Verhältnisse der Nordsee zusammen.