Production of medium-chain-length PHA in octanoate-fed enrichments dominated by Sphaerotilus sp.

Medium-chain-length polyhydroxyalkanoate (mcl-PHA) production by using microbial enrichments is a promising but largely unexplored approach to obtain elastomeric biomaterials from secondary resources. In this study, several enrichment strategies were tested to select a community with a high mcl-PHA storage capacity when feeding octanoate. On the basis of analysis of the metabolic pathways, the hypothesis was formulated that mcl-PHA production is more favorable under oxygen-limited conditions than short-chain-length PHA (scl-PHA). This hypothesis was confirmed by bioreactor experiments showing that oxygen limitation during the PHA accumulation experiments resulted in a higher fraction of mcl-PHA over scl-PHA (i.e., a PHA content of 76 wt% with an mcl fraction of 0.79 with oxygen limitation, compared to a PHA content of 72 wt% with an mcl-fraction of 0.62 without oxygen limitation). Physicochemical analysis revealed that the extracted PHA could be separated efficiently into a hydroxybutyrate-rich fraction with a higher M_w and a hydroxyhexanoate/hydroxyoctanoate-rich fraction with a lower M_w. The ratio between the two fractions could be adjusted by changing the environmental conditions, such as oxygen availability and pH. Almost all enrichments were dominated by Sphaerotilus sp. This is the first scientific report that links this genus to mcl-PHA production, demonstrating that microbial enrichments can be a powerful tool to explore mcl-PHA biodiversity and to discover novel industrially relevant strains.     

Morphological studies on cellular detachment induced by antibody reactions directed against membrane associated antigens. An ultrastructural study

The skin explant model was used to determine the effect of antibody reactions against membrane associated antigens on normal human keratinocytes. Addition of specific allo-antibodies against HLA class I antigens induced characteristic changes in the cells on the outermost region of the explant-outgrowth. A disorganization of the filopodia of these cells occurred and the edges of the cellular border were lifted from the substratum. These signs of detachment were also found when pemphigus serum was added. In both experimental conditions the detachment of the cells was complement independent. After removing the antiserum a recovery took place, but the cells once lifted from the substratum remained recognizable as a ridge of cells. No changes were observed when the explants were incubated with antibodies against HLA class II antigens. Incubation with specific antibodies against HLA class I antigens not present on the explant had also no effect. We propose that antibody reactions against various membrane associated antigens can induce within a few hours characteristic changes of the cellular margins.     

Structural changes of IgG induced by heat treatment and by adsorption onto a hydrophobic Teflon surface studied by circular dichroism spectroscopy

Thermal denaturation of mouse monoclonal immunoglobulin G (isotype 1), as well as structural rearrangements resulting from adsorption on a hydrophobic Teflon surface, are studied by circular dichroism spectroscopy. Both heat-induced and adsorption-induced denaturation do not lead to complete unfolding into an extended polypeptide chain, but leave a significant part of the IgG molecule in a globular or corpuscular form. Heating dissolved IgG causes a decrease of the fractions of β-sheet and β-turn conformations, whereas those of random coil and, to a lesser extent, α-helix increase. Adsorption enhances the formation of α-helices and random coils, but the β-sheet content is strongly reduced. Heating adsorbed IgG results in a gradual break-down of the α-helix and β-turn contents, and a concomitant formation of β-sheet structures. Thus, the structural changes in IgG caused by heating and by adsorption, respectively, are very different. However, after heating, the structure of adsorbed IgG approaches the structure of thermally denatured IgG in solution.     

The relationship between nutrient availability,shoot biomass and species richness in grassland and wetland communities

The relationship was studied between shoot biomass, nutrient concentration in the soil and number of species per unit area. The study was carried out in two different parts of the Netherlands, the Gelderse Vallei (east of Amersfoort) and the Westbroekse Zodden (northwest of Utrecht). Four series of vegetation and soil samples were taken: one series in grassland and wetland communities, one series in grassland communities, one series in fen communities and one series in only one wetland community. The two series in grassland communities show a negative correlation between shoot biomass and species number and a positive correlation between shoot biomass and nutrient concentration in the soil. The opposite was found in the series in the fen communities: there was a positive correlation between species number and shoot biomass and a negative correlation between shoot biomass and nutrient concentrations. The series of samples that had been taken in only one wetland community showed an optimum curve for the relation between shoot biomass and number of species. It is concluded that in the plant communities studied the species richness per unit area increases with increasing productivity at low production levels (< 400–500 g/m²) and decreases with increasing productivity at higher production levels (> 400–500 g/m²).     

Binding of unmodified low-density lipoproteins to human fibroblasts. An investigation by immunoelectron microscopy.

The bindinf of unmodified low density lipoproteins to the plasma membrane of fibroblasts was studied at the ultrastructural level. The bound low density lipoprotein was visualized by an indirect immunoperoxidase technique, with the use of an antiserum against apoprotein B. Immunoreactive regions representing bound apoprotein B were found on the plasma membrane, in indented regions with a diameter of 0.15--0.30 micrometer and a fuzzy coat on the cytoplasmic side. Fibroblasts from a patient homozygous for hyperlipoproteinaemia type IIa showed no immunoreactive material in the indented regions. The specific 125I-labelled low density lipoprotein binding to these homozygous fibroblasts was 7% compared to control fibroblasts.     

Immunoenzymehistochemical demonstration of the binding of low density lipoproteins to cultured human fibroblasts

Summary Using an indirect cytochemical immunoperoxidase technique, we were able to demonstrate the binding of low density lipoprotein to cultured human fibroblasts. With this technique, fibroblasts from a patient suffering from homozygous hyperlipoproteinaemia type IIa did not show this binding.The method described here allows study of the localization of unmodified low density lipoproteins binding to cultured fibroblasts.