Regulation of Bacterioplankton Production and Cell Volume in a Eutrophic Estuary

During three periods of 16 to 25 days, bacterioplankton production, bacterial cell volume, chlorophyll a, CO₂ assimilation, and particulate organic carbon were measured in enclosures situated in the eutrophic estuary Roskilde Fjord, Denmark. The enclosures were manipulated with respect to sediment contact and contents of inorganic nutrients, planktivorous fish, and suspension-feeding bivalves. Nutrient enrichment, the presence of suspension feeders, and sediment contact induced pronounced changes in bacterial production, as well as minor changes in bacterial cell volume; however, these effects seemed to be indirect, transmitted via phytoplankton. Bacterial production, measured as [³H]thymidine incorporation, closely followed changes in phytoplankton biomass and production, with time lags of 5 to 10 days. Good correlations of mean bacterioplankton production to chlorophyll a concentration and CO₂ assimilation suggested phytoplankton to be the dominating source of bacterial substrate, apparently independent of nutrient stress. Zooplankton >140 μm, bivalves, and sediment seemed to provide insignificant, if any, substrate for bacterioplankton, and benthic suspension feeders seemed not to act as direct competitors for dissolved organic carbon. The bacterioplankton mean cell volume, measured by image analysis, changed seasonally, with the smallest cells during the summer. Within each period, the bacterial cell volume correlated positively to growth rate and negatively to temperature.     

Helicobacter pylori interacts with heparin and heparin-dependent growth factors

Abstract The pathogenic bacterium Helicobacter pylori , which causes active, chronic type B gastritis and peptic ulcer disease, and increases the risk for development of gastric cancer, could tentatively interfere with growth factors and growth factor receptors of importance for the gastroduodenal mucosa, e.g. heparin-binding FGFs (fibroblast growth factors). H. pylori binds FGF with an extremely strong affinity (3.8 × 10⁻¹² M), and also heparan sulfate and heparin with higher affinity ( K _d 9 × 10⁻⁹ M) than FGFs bind to heparin (10⁻⁸–10⁻⁹ M). FGF receptors are also dependent on heparin for their activation. Heparan sulfate binding proteins (HSBP) are exposed on and shed from the surface of H. pylori , which often are localised close to the epithelial stem cells in the gastroduodenal glands. H. pylori could thus efficiently interfere with growth factors and growth factor receptors, tentatively resulting in disturbance of the delicate balance that control the renewal, maintenance and repair of the gastroduodenal mucosa. This mode of action has previously not been considered, but may constitute part of its pathogenic mechanism. Such a dynamic mode of action of H. pylori may explain the reason for that infected victims may either suffer from gastrointestinal symptoms or lack clinical evidence of disease or discomfort.     

Effect of cholecystokinin-pancreozymin (CCK-PZ) on glycoprotein secretion from mouse gallbladder epithelium

Summary Structural changes in the gallbladder epithelial cells of the mouse were studied following in vivo and in vitro stimulation of the gallbladder with the gastrointestinal hormone cholecystokinin-pancreozymin (CCK-PZ). Signs of increased secretory activity were observed within the first 2–3 min after hormone administration. At the ultrastructural level, best visualized with the PA-CrA-silver technique, granule discharge was observed, as was an overall increase in size of the granules. After prolonged in vitro incubation or repeated in vivo stimulation, there was an almost total depletion of secretory granules. This phenomenon is accompanied by an enhanced uptake of extracellular thorium dioxide by endocytotic vesicles at the apical cell surface. An exocytosisendocytosis coupling mechanism may be important for membrane conservation in the gallbladder epithelial cells. The findings establish that the hormone CCK-PZ stimulates the secretion of glycoproteins from the mouse gallbladder epithelium.This investigation was supported by grants from the University of Umeå and from the Swedish Medical Research Council (grant No. B76-12X-04758-01). The authors wish to thank Miss K. Karlsson and Miss M. Borg for skilful technical assistance     

Ultrastructural cytochemistry of the secretory granules of the hamster submandibular gland

Summary The ultrastructure and cytochemistry of the secretory granules of the male hamster submandibular salivary gland were studied. After fixation in glutaraldehyde followed by osmium tetroxide the granules exhibit a characteristic bipartite substructure, with an electron lucid crescenteric rim and a more dense central core. A differentiation into two regions of the granules could also be visualized in specimens primarily fixed in Millonig's osmium tetroxide or in potassium permanganate. The electron lucid peripheral portion of the membrane bounded secretory granules further displays a strong positive reaction after staining of ultrathin sections with the periodic acid-chromic acid-(PA-CrA)-silver technique. The strong periodate reactivity of the rim relative to the core, suggests a difference in mucin composition of the two granule regions. With the PA-CrA-silver staining technique a positive reaction was also observed within the Golgi apparatus of the acinar cells.     

Inhibition of lactoferrin and vitronectin binding toStaphylococcus aureus by heparin

Cells ofStaphylococcus aureus strain ISP 546, previously shown to express high binding of vitronectin (Vn), were shown also to bind radioactive iodine-labeled human lactoferrin (Lf). The binding was specific, and heat treatment ofS. aureus cells abolished Lf binding. When cells were preincubated with heparin (2.5 g/ml), binding of Vn and Lf was inhibited by more than 90%. Two other sulfated carbohydrate polymers, fucoidan and dextran sulfate (mol weights 5000 and 8000) inhibited binding of both iodine-labeled Vn and Lf by about 75% each. No synergistic inhibitory effect between heparin and fuocidan on Lf binding byS. aureus was detected. Mannose, mannoseamine and poly--sialic acid (colominic acid) inhibited Vn binding by about 40% but had no effect on Lf binding. A cell surface extract of ISP 546 inhibited Vn binding but did not affect Lf binding. Lf binding toS. aureus was inhibited by preincubation of the cells with Vn, and Vn binding toS. aureus was inhibited by preincubation with Lf. Our data indicate that Vn and Lf bind to different molecules on theS. aureus cell surface, involving heparin and other carbohydrate interactions.     

Immunological Recognition of Fibronectin-Binding Proteins of Staphylococcus aureus and Staphylococcus capitis,Strain LK499

Antibodies to fibronectin-binding proteins (FnBPs) of Staphylococcus aureus, including binding domain of FnBPA, the D region, or the A-C regions of FnBPB were produced in rabbits and mice. These antibodies were used to characterize cell-associated FnBPs of S. aureus strain Cowan I, S. aureus strain U320 and a coagulase-negative Staphylococcus capitis strain LK499 as well as extracellular FnBPs in culture supernatants of the strain U320. FnBPs of S. aureus were predominantly FnBPA, while FnBPB was hardly detected on the cells or in culture supernatant of these S. aureus strains. Moreover, S. capitis strain LK499 possessed different FnBP(s) compared to S. aureus because the antibodies to S. aureus FnBPs did not recognize FnBP(s) on S. capitis.     

Combined serum IgG response to Helicobacter pylori VacA and CagA predicts gastric cancer

Helicobacter pylori is a major factor for the development of gastric cancer. The aim of this study was to define serum antibody patterns associated with H. pylori infection in patients with gastric cancer using a Western blot technique. Serum samples collected from 115 patients with gastric cancer and 110 age- and gender-matched patients without gastrointestinal diseases were tested for IgG antibodies to H. pylori antigens (outer membrane proteins and whole cell preparations). No significant differences were found between patients with and without gastric cancer using outer membrane proteins (82% and 73%, P>0.05) or whole cell antigens (84% and 76%, P>0.05), respectively. The significant differences between patients with and without gastric cancer were associated with bands of 94 kDa (54% and 20%, P<0.001) and 30 kDa (65% and 44%, P<0.01). A combination of antibodies to 85 kDa (VacA) and 120 kDa (CagA) was significantly (P<0.01) more frequent in gastric cancer patients than in patients without gastric cancer. The detection of antibodies to 94- and 30-kDa bands, in association with the determination of serum antibodies to CagA+/VacA+, may have a prospective value in assessment of the risk of developing of gastric cancer.     

Global patterns of diversity and community structure in marine bacterioplankton

Because of their small size, great abundance and easy dispersal, it is often assumed that marine planktonic microorganisms have a ubiquitous distribution that prevents any structured assembly into local communities. To challenge this view, marine bacterioplankton communities from coastal waters at nine locations distributed world-wide were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes, used as operational taxonomic units (OTU). Our survey and analyses show that there were marked differences in the composition and richness of OTUs between locations. Remarkably, the global marine bacterioplankton community showed a high degree of endemism, and conversely included few cosmopolitan OTUs. Our data were consistent with a latitudinal gradient of OTU richness. We observed a positive relationship between the relative OTU abundances and their range of occupation, i.e. cosmopolitans had the largest population sizes. Although OTU richness differed among locations, the distributions of the major taxonomic groups represented in the communities were analogous, and all local communities were similarly structured and dominated by a few OTUs showing variable taxonomic affiliations. The observed patterns of OTU richness indicate that similar evolutionary and ecological processes structured the communities. We conclude that marine bacterioplankton share many of the biogeographical and macroecological features of macroscopic organisms. The general processes behind those patterns are likely to be comparable across taxa and major global biomes.