Qualitative importance of the microbial loop and plankton community structure in a eutrophic lake during a bloom of cyanobacteria

Plankton community structure and major pools and fluxes of carbon were observed before and after culmination of a bloom of cyanobacteria in eutrophic Frederiksborg Slotssø, Denmark. Biomass changes of heterotrophic nanoflagellates, ciliates, microzooplankton (50 to 140 μm), and macrozooplankton (larger than 140 μm) were compared to phytoplankton and bacterial production as well as micro- and macrozooplankton ingestion rates of phytoplankton and bacteria. The carbon budget was used as a means to examine causal relationships in the plankton community. Phytoplankton biomass decreased and algae smaller than 20 μm replacedAphanizomenon after the culmination of cyanobacteria. Bacterial net production peaked shortly after the culmination of the bloom (510 μg C liter^?1 d^?1 and decreased thereafter to a level of approximately 124 μg C liter^?1 d^?1. Phytoplankton extracellular release of organic carbon accounted for only 4–9% of bacterial carbon demand. Cyclopoid copepods and small-sized cladocerans started to grow after the culmination, but food limitation probably controlled the biomass after the collapse of the bloom. Grazing of micro- and macrozooplankton were estimated from in situ experiments using labeled bacteria and algae. Macrozooplankton grazed 22% of bacterial net production during the bloom and 86% after the bloom, while microzooplankton (nauplii, rotifers and ciliates larger than 50 μm) ingested low amounts of bacteria and removed 10–16% of bacterial carbon. Both macro-and microzooplankton grazed algae smaller than 20 μm, although they did not control algal biomass. From calculated clearance rates it was found that heterotrophic nanoflagellates (40–440 ml^?1) grazed 3–4% of the bacterial production, while ciliates smaller than 50 μm removed 19–39% of bacterial production, supporting the idea that ciliates are an important link between bacteria and higher trophic levels. During and after the bloom ofAphanizomenon, major fluxes of carbon between bacteria, ciliates and crustaceans were observed, and heterotrophic nanoflagellates played a minor role in the pelagic food web.     

Iodide transport in primary cultured thyroid follicle cells: evidence of a TSH-regulated channel mediating iodide efflux selectively across the apical domain of the plasma membrane.

The transport of iodide was studied in porcine thyroid follicle cells cultured in bicameral chambers. The continuous layer of polarized follicle cells, joined by tight junctions, formed a diffusion barrier between the two compartments (apical and basal) of the culture chamber. Uptake and efflux of 125I- at either surface (apical and basolateral) of the cells were thus possible to determine. Protein binding of iodide was inhibited by methimazole (10(-3) M) in all experiments. Radioiodide was taken up by the cells from the basal medium in a thyroid-stimulating hormone (TSH)-dose dependent manner with a maximal cell/medium ratio of 125I- of about 50 in cultures prestimulated with 0.1 to 1 mU/ml for 2 days. This uptake was inhibited by perchlorate and ouabain. In contrast, 125I- was not taken up from the apical medium. In preloaded cells, iodide efflux was rapidly (within 1-2 min) and dose-dependently (0.1-10 mU/ml) stimulated by TSH. Bidirectional measurements revealed that TSH stimulated iodide efflux in apical direction, leaving efflux in basal direction unchanged. In experiments with continuous uptake of label from the basal compartment, the TSH-stimulated efflux in apical direction had a duration of 4 to 6 min and resulted in a reduction in the cellular content of radioiodide by up to 80%. Decreased levels of cellular 125I- remained for at least 15 min after TSH addition. From our observations we conclude that the TSH-regulated uptake and efflux of iodide take place at opposite surfaces of the porcine thyroid follicle cell. Acutely stimulated iodide efflux is not the result of an increased permeability for iodide in the entire plasma membrane but only in the apical domain of this membrane. This implicates the presence of an iodide channel mediating TSH-stimulated efflux across the apical plasma membrane of the follicle cell. The mechanism is suggested to facilitate a vectorial transport of iodide in apical direction, i.e., to the lumen of the intact follicle.     

Immuno-histochemical and -cytochemical Evidence Suggesting the Presence of Campylobacter jejuni and Campylobacter coli in Cases of Porcine Intestinal Adenomatosis

Antisera against a number of Campylobacter species were used in immuno-histochemical and -cytochemical studies on cases of porcine intestinal adenomatosis. Avidin-biotin-complex (ABC) and streptavidin immunoperoxidase methods were used on formalin-fixed, paraffin-embedded and frozen sections. Protein A gold method was used on formaldehyde fixed and frozen sections for immuno-cytochemistry. The antisera used were raised in rabbits by subcutaneous or intravenous injection of living or formalin treated organisms. Antisera against different serotypes of the thermotolerant, catalase positive Campylobacters, Campylobacter jejuni and Campylobacter coli gave positive reactions in the immuno-histochemical studies. The staining was found in intestinal epithelial cells both in the ileum and in the colon and was restricted to the apical cytoplasm of adenomatous epithelial cells. The staining had a granular pattern, the positive structures sometimes having the shape of Campylobacter. Epithelial cells in areas with normal differentiation of goblet cells did not stain. In contrast, no staining resulted with antisera against Campylobacter sputorum subsp. mucosalis and Campylobacter hyointestinalis. Immuno-cytochemistry, using antisera against Campylobacter jejuni showed that the positive staining in altered epithelial cells were restricted to intracellular organisms having a structure resembling Campylobacter spp.     

Regulation of Ca2+-activated K+ Channel from Rabbit Distal Colon Epithelium by Phosphorylation and Dephosphorylation

The Ca²⁺-activated maxi K⁺ channel is predominant in the basolateral membrane of the surface cells in the distal colon. It may play a role in the regulation of the aldosterone-stimulated Na⁺ reabsorption from the intestinal lumen. Previous measurements of these basolateral K⁺ channels in planar lipid bilayers and in plasma membrane vesicles have shown a very high sensitivity to Ca²⁺ with a K _0.5 ranging from 20 nm to 300 nm, whereas other studies have a much lower sensitivity to Ca²⁺. To investigate whether this difference could be due to modulation by second messenger systems, the effect of phosphorylation and dephosphorylation was examined. After addition of phosphatase, the K⁺ channels lost their high sensitivity to Ca²⁺, yet they could still be activated by high concentrations of Ca²⁺ (10 μm). Furthermore, the high sensitivity to Ca²⁺ could be restored after phosphorylation catalyzed by a cAMP dependent protein kinase. There was no effect of addition of protein kinase C. In agreement with the involvement of enzymatic processes, lag periods of 30–120 sec for dephosphorylation and of 10–280 sec for phosphorylation were observed. The phosphorylation state of the channel did not influence the single channel conductance. The results demonstrate that the high sensitivity to Ca²⁺ of the maxi K⁺ channel from rabbit distal colon is a property of the phosphorylated form of the channel protein, and that the difference in Ca²⁺ sensitivity between the dephosphorylated and phosphorylated forms of the channel protein is more than one order of magnitude. The variety in Ca²⁺ sensitivities for maxi K⁺ channels from tissue to tissue and from different studies on the same tissue could be due to modification by second messenger systems. Received: 28 February 1995/Revised: 22 December 1995     

Constitutively hyposialylated human T-lymphocyte clones in the Tn-syndrome: binding characteristics of plant and animal lectins

Previously, 1,3-galactosyltransferase-deficient (Tn+) and normal (TF+) T-lymphocyte clones have been established from a patient suffering from Tn-syndrome [Thurnheret al. (1992)Eur J Immunol 22: 1835–42], Tn+ T lymphocytes express only Tn antigen (GalNAc1-O-R) while other O-glycan structures such as sialosyl-Tn (Neu5Ac2,6GalNAc1-O-R) or TF (Gal1-3GalNAc1-O-R) antigens are absent from these cells as shown by flow cytometry using specific mABs for TF and sialosyl-Tn antigen, respectively. Normal T lymphocytes express the TF antigen and derivatives thereof. The surface glycans of Tn+ and TF+ cells were then analysed by flow cytometry using the following sialic acid-binding lectins:Amaranthus caudatus (ACA),Maackia amurensis (MAA),Limax flavus (LFA),Sambucus nigra (SNA) andTriticum vulgare (WGA). Equal and weak binding of MAA and SNA to both TF+ and Tn+ cells was found. WGA, LFA and ACA bound more strongly to TF+ cells than to Tn+ cells. Binding of ACA to TF+ cells was enhanced after sialidase treatment. To investigate the possible biological consequences of hyposialylation, binding of three sialic acid-dependent adhesion molecules to Tn+ and TF+ cells was estimated using radiolabelled Fc-chimeras of sialoadhesin (Sn), myelin-associated glycoprotein (MAG) and CD22. Equal and strong binding of human CD22 to both TF+ and Tn+ cells was found. Whereas binding of Sn and MAG to TF+ cells was strong (100%), binding to Tn+ cells amounted only to 33% (Sn) and 19% (MAG). These results indicate that thein vivo interactions of T lymphocytes in the Tn syndrome with CD22 are not likely to be affected, whereas adhesion mediated by Sn or MAG could be strongly reduced.     

Fungal protoplasts as tools for studies on protein secretion

Summary Protoplasts were prepared from mycelium of Aspergillus niger N-402. Sucrose was used to induce the synthesis and secretion of invertase. Protoplasts secreted 2 forms of invertase, different to those secreted by the mycelium. ¹⁴C mannose was shown to be taken up by protoplasts and incorporated into secreted proteins.     

Colonial breeding and speciation in birds

Summary It was recently suggested that bird species which breed colonially might be under stronger sexual selection, have faster rates of evolution and might therefore speciate more rapidly than bird species which do not. If true, then colonial taxa should contain more species than non-colonial taxa, other things being equal. When similarity through common descent is accounted for, there is little evidence for an association between the number of species in a clade and whether it is colonial or not.     

Influence of protein conditioning films on binding of a bacterial polysaccharide adhesin from Hyphomonas MHS-3

A putative polysaccharide adhesin which mediates non-specific attachment of Hyphomonas MHS-3 (MHS-3) to hydrophilic substrata has been isolated and partially characterized. A polysaccharide-enriched portion of the extracellular polymeric substance (EPS(P)) from MHS-3 was separated into four fractions using high performance size exclusion chromatography (HPSEC). Comparison of chromatograms of EPS(P) from MHS-3 and a reduced adhesion strain (MHS-3 rad) suggested that one EPS(P) fraction, which consisted of carbohydrate, served as an adhesin. Adsorption of this fraction to germanium (Ge) was investigated using attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectrometry. Binding curves indicated that the isolated fraction had a relatively high affinity for Ge when ranked against an adhesive protein from Mytilis edulis, mussel adhesive protein (MAP) and an acidic polysaccharide (alginate from Macrocystis pyrifera). Spectral features were used to identify the fraction as a polysaccharide previously reported to adsorb preferentially out of the EPS(P) mixture. Conditioning the Ge substratum with either bovine serum albumin (BSA) or MAP decreased the adsorption of the adhesive polysaccharide significantly. Conditioning Ge with these proteins also decreased adhesion of whole cells.     

Enzyme production in a cell recycle fermentation system evaluated by computer simulations

Enzyme production in a cell recycle fermentation system was studied by computer simulations, using a mathematical model of -amylase production by Bacillus amyloliquefaciens. The model was modified so as to enable simulation of enzyme production by hypothetical organisms having different production kinetics at different fermentation conditions important for growth and production. The simulations were designed as a two-level factorial assay, the factor studied being fermentation with or without cell recycling, repression of product synthesis by glucose, kinetic production constants, product degradation by a protease, mode of fermentation, and starch versus glucose as the substrate carbon source.The main factor of importance for ensuring high enzyme production was cell recycling. Product formation kinetics related to the stationary growth phase combined with continuous fermentation with cell recycling also had a positive impact. The effect was greatest when two or more of these three factors were present in combinations, none of them alone guaranteeing a good result. Product degradation by a protease decreased the amount of product obtained; however, when combined with cell recycling, the protease effect was overshadowed by the increased production. Simulation of this type should prove a useful tool for analyzing troublesome fermentations and for identifying production organisms for further study in integrated fermentation systems.List of Symbols a proportionality constant relating the specific growth rate to the logarithm of G (h) - a ₁ reaction order with respect to starch concentration - a ₂ reaction order with respect to glucose concentration - c starch concentration (g/l) - c ₀ starch concentration in the feed (g/l) - D dilution rate (h^–1) - e intrinsic intracellular amylase concentration (g product/g cell mass) - E extracellular amylase concentration (g/l) - F volumetric flow rate (l/h) - G average number of genome equivalents of DNA/cell - K ₁ intracellular repression constant - K ₂ intracellular repression constant - K _s Monod saturation constant (g/l) - k ₃ product excretion rate constant (h^–1) - k _I translation constant (g product/g mRNA/h) - k _d first order decay constant (h^–1) - k _dw first order decay constant (h^–1) - k _gl rate constant for glucose production (g/l/h) - k _{m, dgr} saturation constant for product degradation (g/l) - k _st rate constant for starch hydrolysis (g/l/h) - k _t1 proportionality constant for amylase production (g mRNA/g substrate) - k _t2 proportionality constant for amylase production (g mRNA *h/g substrate) - k _w protease excretion rate constant (h^–1) - k _wt1 proportionality constant for protease production (g mRNA/g substrate) - k _wt2 proportionality constant for protease production (g mRNA *h/g substrate) - k _wI translation constant (g protease/g mRNA/h) - m maintenance coefficient (g substrate/g cell mass/h) - n number of binding sites for the co-repressor on the cytoplasmic repressor - Q repression function, K₁/K₂ less than or equal to 1.0 - Q _w repression function, K₁/K₂ less than or equal to 1.0 - r intrinsic amylase mRNA concentration (g mRNA/g cell mass) - r _m intrinsic protease mRNA concentration (g mRNA/g cell mass) - R _ex retention by the filter of the compounds x=: C starch, E amylase, or S glucose - R _t amylase transport rate (g product/g cell mass/h) - R _wt protease transport rate (g protease/g cell mass/h) - R _s rate of glucose production (g/l/h) - R _c rate of starch hydrolysis (g/l/h) - S ₀ feed concentration of free reducing sugar (g/l) - s extracellular concentration of reducing sugar (g/l) - t time (h) - V volume (1) - w intracellular protease concentration (g/l) - W extracellular protease concentration (g/l) - X cell mass concentration (dry weight) (g/l) - Y yield coefficient (g cell mass/g substrate) - substrate uptake (g substrate/g cell mass/h) - specific growth rate of cell mass (h^–1) - _d specific death rate of cells (h^–1) - _m maximum specific growth rate of cell mass (h^–1) - _m,dgr maximum specific rate of amylase degradation (h^–1) This study was supported by the Nordic Industrial Foundation Bioprocess Engineering Programme and the Center for Process Biotechnology, The Technical University of Denmark.