Sequences homologous to Tc(s) transposable elements ofCaenorhabditis elegans are widely distributed in the phylum nematoda

Summary To have a better understanding of the evolutionary history of mobile elements within the nematodes, we examined the distribution and the conservation of homologues to transposable elements fromCaenorhabditis elegans (Tc1, Tc2, Tc3, Tc4, Tc5, and FB1) in 19 nematode species belonging to the class Secernentea. Our results show that Tc1 elements display a distribution restricted to the family Rhabditidae with poor conservation. The Tc2 and FB1 homologous elements have the same patchy distribution within the Rhabditidae. They were only found inCaenorhabditis and inTeratorhabditis. The Tc3 element is widely distributed among nematode species. Tc3 homologous elements are present in the majority of the Rhabditidae but also in two genera within the family Panagrolaimidae, and inBursaphelenchus, which belongs to the order Aphelenchida. Tc4 and Tc5 homologues show the most limited distribution of all tested elements, being strictly limited toC. elegans. These data indicate that in some cases, the distribution of transposable elements in the nematode cannot be explained by strict vertical transmission. The distribution of Tc3, Tc4, and Tc5 suggests that horizontal transmission may have occurred between reproductively isolated species during their evolutionary history.     

Cyst hatching in Anostraca accelerated by retinoic acid,amplified by Calcium Ionophore A23187, and inhibited by Calcium-channel blockers

Cyst hatching, under standardized conditions, of the Anostracan species Thamnocephalus platyurus and Streptocephalus dichotomus was significantly accelerated but not increased by applying the morphogen retinoic acid (RA). Cyst hatching was enhanced but not accelerated by artificially increasing the inflow of Ca²⁺ to the embryonic cells, using Calcium Ionophore A 23 187. Cyst hatching was accelerated and amplified, to a level in excess of the summed effects of each treatment, by a combined application of RA and ionophore. It was inhibited almost quantitatively by the Calcium-channel blockers Nifedipin and Verapamil. The significance of these findings is discussed.     

Influence of the mode of reactor operation on the rate and yield of fermentation of the model solid substrate,wheat bran,by a microbial consortium under non-axenic anaerobic conditions

Summary Anaerobic fermentation of wheat bran, a model solid substrate, was conducted under non-axenic conditions, in two reactors operated under different modes, all other conditions being strictly identical. The first reactor was a completely-mixed batch reactor. The second reactor was a percolator into which the liquid phase was recirculated in closed loop through the solid substrate acting as a stationary bed. The final yield of fermentation was obtained after 27 days in the completely-mixed batch reactor, and after 14 days only in the percolator. Scanning electron microscopy revealed that numerous micro-organisms adhered to the solid substrate acting as a carrier in the percolator, whereas only very few micro-organisms adhered to the solid substrate in the completely-mixed batch reactor. The results show that obtaining a durable direct contact between micro-organisms and their solid substrate improves the rate of solids degradation.     

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Production of Cell Wall-Degrading Enzymes by the Phytopathogenic Fungus Sclerotinia sclerotiorum

The range of polysaccharide-degrading enzymes and glycosidases formed by the phytopathogenic fungus Sclerotinia sclerotiorum was monitored following growth on 16 carbohydrate substrates. Endo- and exoenzymes capable of degrading cellulosic, hemicellulosic, and pectinolytic polysaccharides were secreted. Pectinolytic activities were produced constitutively on all of the substrates tested. Cellulolytic enzymes were not induced in simple sugar (i.e., glucose or xylose) media. Polysaccharide growth substrates and cellulase inducers increased all of the enzyme activities tested. Gel filtration analysis revealed the appearance of new molecular forms of pectinase, β-xylosidase, and cellobiosidase during induction on pectin and carboxymethyl cellulose media.     

Localisation of degradative enzymes in white-rot decay of lignocellulose

The use of immunogold-cytochemical labelling techniques in electron microscopy of wood infected by basidiomycete fungi has assisted in the elucidation of the localisation of enzymes which degrade lignocellulose. The use of specific immunocytochemical techniques is discussed with respect to the authenticity and accuracy of the methods, the use of adequate controls in the gold-labelling procedure, and the immunospecificity of the antibodies.Localisation of the lignin-degrading enzymes, lignin-peroxidase and laccase, has shown that these enzymes do not bind to wood cell walls unless the process of decay has already commenced. Similarly localisation of cellulases Endoglucanase II (EGII) and Cellobiohydrolase I (CBHI) has shown that these enzymes only bind to exposed ends of cellulose fibrils and to partially degraded areas of the wood cell wall. -Glucosidase is always immobilised within the extracellular polysaccharide layer surrounding fungal hyphae.This review postulates that there is regulation of the release sequence of these lignocellulolytic enzymes defining the spatial arrangement between the hyphae and the wood cell wall. This hypothesis is presented diagrammatically.     

Anaerobic degradation of sorbic acid by sulfate-reducing and fermenting bacteria: pentanone-2 and isopentanone-2 as byproducts

Strictly anaerobic bacteria were enriched and isolated from freshwater sediment sources in the presence and absence of sulfate with sorbic acid as sole source of carbon and energy. Strain WoSo1, a Gram-negative vibrioid sulfate-reducing bacterium which was assigned to the species Desulfoarculus (formerly Desulfovibrio) baarsii oxidized sorbic acid completely to CO₂ with concomitant stoichiometric reduction of sulfate to sulfide. This strain also oxidized a wide variety of fatty acids and other organic compounds. A Gram-negative rod-shaped fermenting bacterium, strain AmSo1, fermented sorbic acid stoichiometrically to about equal amounts of acetate and butyrate. At concentrations higher than 10 mM, sorbic acid fermentation led to the production of pentanone-2 and isopentanone-2 (3-methyl-2-butanone) as byproducts. Strain AmSo1 fermented also crotonate and 3-hydroxybutyrate to acetate and butyrate, and hexoses to acetate, ethanol, hydrogen, and formate. The guanine-plus-cytosine content of the DNA was 41.8±1.0 mol%. Sorbic acid at concentrations higher than 5 mM inhibited growth of this strain while strain WoSo1 tolerated sorbic acid up to 10 mM concentration.     

On predatory tendencies in the feeding ecology of the fairy shrimp Streptocephalus proboscideus (Frauenfeld, 1873) (Crustacea: Anostraca)

The feeding habits of the filter-feeding fairy shrimp Streptocephalus proboscideus are documented experimentally by offering them ciliates, Volvox, rotifers, nematodes and small crustaceans as prey. Escape capabilities (e.g. swimming speed) rather than size or shape were found to determine these animals' vulnerability to predation by the fairy shrimp. Ingestion rates for Volvox increased hyperbolically with size and, at the high temperatures in which they live, fairy shrimps may daily remove the equivalent of their body weight from the environment.