Sulfide induces phosphate release from polyphosphate in cultures of a marine Beggiatoa strain

Sulfur bacteria such as Beggiatoa or Thiomargarita have a particularly high capacity for storage because of their large size. In addition to sulfur and nitrate, these bacteria also store phosphorus in the form of polyphosphate. Thiomargarita namibiensis has been shown to release phosphate from internally stored polyphosphate in pulses creating steep peaks of phosphate in the sediment and thereby inducing the precipitation of phosphorus-rich minerals. Large sulfur bacteria populate sediments at the sites of recent phosphorite formation and are found as fossils in ancient phosphorite deposits. Therefore, it can be assumed that this physiology contributes to the removal of bioavailable phosphorus from the marine system and thus is important for the global phosphorus cycle. We investigated under defined laboratory conditions which parameters stimulate the decomposition of polyphosphate and the release of phosphate in a marine Beggiatoa strain. Initially, we tested phosphate release in response to anoxia and high concentrations of acetate, because acetate is described as the relevant stimulus for phosphate release in activated sludge. To our surprise, the Beggiatoa strain did not release phosphate in response to this treatment. Instead, we could clearly show that increasing sulfide concentrations and anoxia resulted in a decomposition of polyphosphate. This physiological reaction is a yet unknown mode of bacterial polyphosphate usage and provides a new explanation for high phosphate concentrations in sulfidic marine sediments.     

Enhancer of Polycomb is a suppressor of position-effect variegation in Drosophila melanogaster.

Polycomb group (PcG) genes of Drosophila are negative regulators of homeotic gene expression required for maintenance of determination. Sequence similarity between Polycomb and Su(var)205 led to the suggestion that PcG genes and modifiers of position-effect variegation (PEV) might function analogously in the establishment of chromatin structure. If PcG proteins participate directly in the same process that leads to PEV, PcG mutations should suppress PEV. We show that mutations in E(Pc), an unusual member of the PcG, suppress PEV of four variegating rearrangements: In(l)wm4, B(SV), T(2;3)Sb(V) and In(2R)bw(VDe2). Using reversion of a Pelement insertion, deficiency mapping, and recombination mapping as criteria, homeotic effects and suppression of PEV associated with E(Pc) co-map. Asx is an enhancer of PEV, whereas nine other PcG loci do not affect PEV. These results support the conclusion that there are fewer similarities between PcG genes and modifiers of PEV than previously supposed. However, E(Pc) appears to be an important link between the two groups. We discuss why Asx might act as an enhancer of PEV.     

Localization and Pattern of Graviresponse across the Pulvinus of Barley Hordeum vulgare

Pulvini of excised stem segments from barley (Hordeum vulgare cv `Larker') were pretreated with 1 millimolar coumarin before gravistimulation to reduce longitudinal cell expansion and exaggerate radial cell enlargement. The cellular localization and pattern of graviresponse across individual pulvini were then evaluated by cutting the organ in cross-section, photographing the cross-section, and then measuring pulvinus thickness and the radial width of cortical and epidermal cells in enlargements of the photomicrographs. With respect to orientation during gravistimulation, we designated the uppermost point of the cross-section 0° and the lowermost point 180°. A gravity-induced increase in pulvinus thickness was observable within 40° of the vertical in coumarin-treated pulvini. In upper halves of coumarin-treated gravistimulated pulvini, cells in the inner cortex and inner epidermis had increased radial widths, relative to untreated gravistimulated pulvini. In lower halves of coumarin-treated pulvini, cells in the central and outer cortex and in the outer epidermis showed the greatest increase in radial width. Cells comprising the vascular bundles also increased in radial width, with this pattern following that of the central cortex. These results indicate (a) that all cell types are capable of showing a graviresponse, (b) that the graviresponse occurs in both the top and the bottom of the responding organ, and (c) that the magnitude of the response increases approximately linearly from the uppermost point to the lowermost. These results are also consistent with models of gravitropism that link the pattern and magnitude of the graviresponse to graviperception via statolith sedimentation.     

Endothelin action on vascular smooth muscle involves inositol trisphosphate and calcium mobilization

Cultured endothelial cells release a potent vasoconstrictor peptide, endothelin. Cumulative addition of synthetic endothelin to isolated rabbit aortic rings elicited a concentration-dependent increase in contractile tension which was endothelium-independent. In cultured rabbit vascular smooth muscle cells loaded with the fluorescent dye fura 2, endothelin induced a concentration-dependent increase in [Ca2+]i over the range of 0.01 to 100 nM. Moreover, in the absence of extracellular Ca2+, endothelin could still induce an increase in [Ca2+]i. In addition, endothelin stimulated 45Ca2+ efflux from preloaded vascular smooth muscle cells in the presence and absence of extracellular Ca2+, as well as stimulating 45Ca2+ influx in a concentration-dependent manner. Measurement of inositol phosphates in [3H]-myoinositol-labelled vascular vascular trisphosphate. Unlabelled endothelin inhibited (125I)-endothelin binding to cultured rabbit vascular smooth muscle cells in a concentration-dependent manner. Binding was not inhibited by other vasoactive hormones or calcium channel ligands, suggesting cell surface receptors specific for endothelin. We conclude that one of the initial membrane events in the action of endothelin is to induce phospholipase C-stimulated PIP2 hydrolysis and that this signalling mechanism is initiated by endothelin/receptor interaction at the plasma membrane.     

The haplotype distribution of the ΔF508 mutation in cystic fibrosis families in Scotland

Summary The gene defective in cystic fibrosis (CF) has recently been isolated and the major mutation identified. The haplotype distribution of this mutation (ΔF508) has been determined for 215 CF chromosomes in the Scottish population. ΔF508 represents 73% of all CF mutations in this group. There remains considerable linkage disequilibrium between XV2c and KM19 and other mutations in the CF gene.     

High colony-forming efficiency of primary human tumor cells cultured in the adhesive-tumor-cell culture system: improvements with medium and serum alterations

The colony-forming efficiency (CFE) of primary human tumor cells cultured in the adhesive-tumor-cell culture system (ATCCS) using Ham's F12 (F12) or Eagle's minimum essential medium, alpha modification (alphaMEM) and culture medium supplemented with either swine, equine or bovine sera were compared. AlphaMEM supplemented with equine serum provided the highest CFE of the combinations. The CFE increase due to the change from F12 to alphaMEM was approximately 5-fold, and the increase due to the change in serum from swine to equine was approximately 2-fold. Cytokeratin staining showed that this increase was not due to fibroblast growth. The high-average CFE with alphaMEM, approximately 3%, means that an inoculum of only 2 X 10(3) cells is needed to achieve formation of approximately 65 colonies in control cultures, thereby increasing the performance of this system when used in a chemosensitivity assay.