The effect of sedimentation and microbial nitrogen regeneration in a plankton community: a simulation investigation

A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto ‘new production’ and ‘regenerated production’.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom.     

Multimeric bivalent immunogens from recombinant tetanus toxin H<Subscript>C</Subscript> fragment,synthetic hexasaccharides,and a glycopeptide adjuvant

Using recombinant tetanus toxin H_C fragment (rTT-H_C) as carrier, we prepared multimeric bivalent immunogens featuring the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Ogawa, in combination with either the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Inaba, or a synthetic disaccharide tetrapeptide peptidoglycan fragment as adjuvant. The conjugation reaction was effected by squaric acid chemistry and monitored in virtually real time by SELDI-TOF MS. In this way, we could prepare well-defined immunogens with predictable carbohydrate–carrier ratio, whose molecular mass and the amount of each saccharide attached could be independently determined. The ability to prepare such neoglycoconjugates opens unprecedented possibilities for preparation of conjugate vaccines for bacterial diseases from synthetic carbohydrates.     

Effects of the removal of adherent and phagocytic cells on the spleen cell lymphoproliferative response of tumor-bearing mice

Summary Cell-mediated immunity was investigated in two BALB/c mouse tumor systems using the lymphoblastogenesis test with phytohemagglutinin as the mitogen. This lymphoproliferative response was quantitated using the Stimulation Index (SI). There was little evidence for suppressor cell activity in cell mixing experiments in which spleen cells from #51 cell-injected mice were mixed with spleen cells from normal mice. Following macrophage removal by Sephadex G-10 columns and carbonyl iron ingestion, there were no significant changes in the SI values for spleen cells from the #51 cell-injected mice. In contrast, spleen cells from mice injected with H238 cells, a herpes virus-transformed cell line, had a significantly lower SI value than that of normal mice. Suppressor cell activity was demonstrated in cell mixing experiments in which spleen cells from H238 cell-injected mice were mixed with normal spleen cells. Removal of adherent cells from spleen cells from H238 cell-injected mice by Sephadex G-10 columns restored the SI value to that of normal mice. An increased SI value was also seen after removal of phagocytic cells by carbonyl iron. These results suggested that cells with the functional properties of macrophages played an important part in the immunosuppression observed in the H238 tumor system. Comparison of the two macrophage depletion methods suggested that another cell population was also involved in the suppressive effect. Results of immunofluorescent techniques with anti-Lyt-1 and anti-Lyt-2 monoclonal antibodies show these cells to be Ly 1^–, Ly 2,3⁺ phenotypes of T-lymphocytes.     

Enzymic saccharification of sugar beet pulp

Culture filtrates of Talaromyces emersonii UCG 208 grown on beet pulp can convert the polysaccharide components of this agricultural waste to soluble sugars. The saccharification process is facilitated if the pulp is milled or incubated with alkali or peracetic acid before addition of enzyme. However, treatment of unmilled pulp with commercial pectinase prior to incubation with Talaromyces filtrate is also very effective; under suitable conditions, complete hydrolysis of total polysaccharides has been achieved.     

Sorption of Talaromyces emersonii cellulase on cellulosic substrates

The sorption characteristics of the cellulase system of Talaromyces emersonii on various cellulosic substrates were examined. Analysis of reaction mixture supernatants by electrophoresis and enzyme assay showed that all components of the cellulase system were rapidly adsorbed by cellulose and then gradually returned to the liquid phase as the hydrolysis of the substrate progressed. The extent of adsorption in the rapid phase was influenced by pH, temperature, the nature of the substrate, and its concentration.     

PEG-mediated expression of GUS and CAT genes in protoplasts from embryogenic suspension cultures of Picea glauca

ß-Glucuronidase (GUS) and chloramphenicol acetyl transferase (CAT) were used as reporter proteins in protoplasts from embryogenic suspension cultures of Picea glauca (Moench) Voss (white spruce). Plasmid DNA enclosing chimeric GUS and CAT constructs, using the cauliflower mosaic virus 35S promoter, was introduced into Picea glauca protoplasts using polyethylene glycol (PEG). Transient expression was detected 12 to 40 h after PEG-mediated DNA delivery. Dose-response curves using covalently closed circular plasmid DNA, in the absence of carrier DNA, have been obtained for each of these reporter genes. Linearized plasmid DNA gave lower levels of expression than covalently closed circular plasmid DNA when assayed 40 h after PEG-mediated DNA transfer. The use of carrier DNA (herring sperm DNA), in combination with covalently closed circular plasmid DNA, increased the level of expression of GUS by about 50%. CAT expression was enhanced if PEG-mediated delivery was performed on ice rather than at room temperature. The highest level of expression for CAT, and the lowest signal-to-noise ratio, was found 24 h after PEG-mediated DNA transfer. Both GUS and CAT provided results that were quantifiable and can therefore be used as reporter genes in Picea glauca.Abbreviations CAT chloramphenicol acetyl transferase - GUS ß-glucuronidase - CaMV cauliflower mosaic virus - NOS nopaline synthase - CCC covalently closed circular DNA - L linear DNA - PEG polyethylene glycol - HS herring sperm DNA - P protoplasts - PCM protoplast culture medium - MES morpholinoethane-sulfonic acid - Cm chloramphenicol - Ac acetylated - MUG 4-methyl umbelliferyl ß-D-glucuronide - TLC thin layer chromatography     

Presymptomatic testing for Huntington's disease

Summary Presymptomatic testing for Huntington's disease (HD) is possible through the use of restriction fragment length polymorphisms (RFLPs) at the closely linked D4S10 locus. Recombination between the HD and D4S10 loci will occur in 4%–5% of meioses, and is a well-recognised complication of predictive testing. Recombination between RFLPs within the D4S10 locus is a rare event and can usually be ignored. We report a case where such an intra-locus recombination frustrated attempts to predict the chance of a high-risk individual inheriting the HD gene.     

Specific truncations of an acetolactate synthase gene from Brassica napus efficiently complement ilvB/ilvG mutants of Salmonella typhimurium

Summary The expression of an acetolactate synthase (ALS) gene isolated from the cruciferous plant Brassica napus was investigated in Salmonella typhimurium. Using an expression plasmid containing the highly active trc (trp-lac) promoter, several plant ALS constructs were made containing successive in-frame truncations from the 5 end of the coding region. Functional complementation by these plant ALS constructs of a S. typhimurium mutant devoid of ALS enzymic activity was assayed on minimal medium. Truncations which eliminated a large portion of the transit peptide coding sequence proved to act as efficient ALS genes in the bacterial host. Truncations close to the putative processing site of the plant protein were inactive in the complementation test. A full length copy of the gene, including the entire transit peptide coding region, was also inactive. The efficiency of the complementation, estimated by comparison to the growth rate of wild-type S. typhimurium, was found to correlate with levels of ALS activity in the transformed bacteria. Specific mutations, known to produce herbicide resistance in plants, were introduced into the truncated ALS coding sequence by site-directed mutagenesis. When expressed in bacteria these constructs conferred a herbicide resistance phenotype on the host. The potential of this system for mutagenesis and enzymological studies of plant proteins is discussed.     

Ethylene Binding and Action in Rice Seedlings

The existence of at least two saturable, high affinity bindingsites for ethylene is demonstrated in rice seedlings. The sitesdiffer markedly in their rates of association and dissociation.Suppression of endogenous ethylene biosynthesis leads to a significantenhancement of the [¹⁴C]ethylene binding observed. Norbornadieneinhibits ethylene binding and promotion of growth by ethylene.Carbon dioxide and hypoxia promote growth but neither affectsethylene binding. (Received June 25, 1990; Accepted August 24, 1990)