Food web manipulation in Lake Zwemlust: Positive and negative effects during the first two years

The hypertrophic Lake Zwemlust, a small water body used as a swimming pool, was characterized by algal blooms in summer, reducing the Secchi disk transparency to less than 0.3 m. Since in The Netherlands a Secchi disk transparency of 1 m is obligatory for swimming waters, corrective measures were called for to improve the light climate of the lake. In March, 1987, as an experiment, the lake was drained by pumping out the water to facilitate fish elimination. Planktivorous and benthivorous fish species, which were predominant, were removed by seine- and electro-fishing. After the lake had refilled by seepage it was restocked by a new simple fish community comprising pike (Esox lucius) and rudd (Scardinius erythrophthalmus) only. Stacks of willow twigs (Salix) and macrophytes (roots ofNuphar lutea and seedlings ofChara globularis) were introduced into the lake as spawning grounds and refuges for the pike against cannibalism and as shelter for the zooplankton. The effects of this food web manipulation on the light climate, phytoplankton, zooplankton, fish, macrophytes, macrofauna and on the nutrient concentrations were monitored during 1987 and 1988. In summer 1987, despite of high nutrient concentrations, the phytoplankton density was low, due to control by zooplankton, causing a Secchi disk transparency of 2.5 m, the maximum depth. Chlorophyll-a concentrations were low (<5 g Chl.l^–1), blooms of cyanobacteria did not occur and a shift from rotifers to cladocerans took place. In 1988, however, also some negative effects were noticed. Macrophytes and filamentous green algae reached a much higher biomass (50–60% cover of the lake bottom) than in 1987; some species, growing through the entire water column, interfered with the lake's recreational use. Associated with the macro-vegetation and possibly with the absence of larger cyprinids, the diet of which also comprises snails, a large scale development of the snail population, among themLymnaea peregra var.ovata took place. This species is known to act as an intermediate host of the bird-parasitizing trematodeTrichobilharzia ocellata, the cercariae of which cause an itching sensation at the spot of penetration of the human skin, accompanied by rash (schistosome dermatitis or swimmers' itch); in July, 1988, about 40% of the bathers complained about this itching. A positive effect of the macrophytes and filamentous green algae was the high uptake of nitrogen, resulting in a low nitrogen concentration in the lake and growth limitation of the phytoplankton population by nitrogen in the summer of 1988. In 1988 the cladocerans were abundant in April only; and unlike in 1987, in the summer of 1988 there was a shift from cladocerans to rotifers. Therefore, only in early spring (April) zooplankton grazing controlled phytoplankton growth and in summer nitrogen limitation was the major controlling factor, keeping chlorophyll-a concentrations low.     

血吸虫基因操作研究进展

近年来,血吸虫基因组、转录组、蛋白质组和分泌组研究广泛开展,迫切需要针对单个分子功能深入研究。开展血吸虫基因操作研究不仅可在虫体内深入研究基因功能,对进一步理解血吸虫生长发育机理和寄生生活特征具有重要意义,还可建立抗血吸虫候选疫苗和药物靶标筛选的重要平台。为此,本文总结基因操作技术在血吸虫学中的应用并分析其现状。     

The morphology and reproductive status of female Schistosoma mansoni following separation from male worms

Popiel I., Cioli D. and Erasmus D. A. 1984. The morphology and reproductive status of female Schistosoma mansoni following separation from male worms. International Journal for Parasitology14: 183–190. Sexually mature females of Schistosoma mansoni were separated from their male partners and surgically transferred to Nile rats (Arvicanthis niloticus). Over a period of 35 days there was a significant decrease in size of these worms and regression of the reproductive system took place. Electron microscope observations of the vitelline gland and ovary provided details of and a time scale for the regressive changes which took the form of a cessation of cell differentiation and turnover, together with extensive cell death. Survival of cells within these organs was restricted to the undifferentiated cells and by day 35 the worms resembled immature females. It is concluded that regression of the female reproductive system was the result of discontinued male stimulation.The nature and implications of the obligatory relationship between male and female S. mansoni are discussed.     

Differential proteomic analysis of laser-microdissected penetration glands of avian schistosome cercariae with a focus on proteins involved in host invasion

Schistosome invasive stages, cercariae, leave intermediate snail hosts, penetrate the skin of definitive hosts, and transform to schistosomula which migrate to the final location. During invasion, cercariae employ histolytic and other bioactive products of specialized holocrine secretory cells – postacetabular (PA) and circumacetabular (CA) penetration glands. Although several studies attempted to characterize protein composition of the in vitro-induced gland secretions in Schistosoma mansoni and Schistosoma japonicum, the results were somewhat inconsistent and dependent on the method of sample collection and processing. Products of both gland types mixed during their secretion did not allow localization of identified proteins to a particular gland. Here we compared proteomes of separately isolated cercarial gland cells of the avian schistosome Trichobilharzia szidati, employing laser-assisted microdissection and shotgun LC-MS/MS, thus obtaining the largest dataset so far of the representation and localization of cercarial penetration gland proteins. We optimized the methods of sample processing with cercarial bodies (heads) first. Alizarin-pre-stained, chemically non-fixed samples provided optimal results of MS analyses, and enabled us to distinguish PA and CA glands for microdissection. Using 7.5 × 10⁶ μm³ sample volume per gland replicate, we identified 3347 peptides assigned to 792 proteins, from which 461 occurred in at least two of three replicates in either gland type (PA = 455, 40 exclusive; CA = 421, six exclusive; 60 proteins differed significantly in their abundance between the glands). Peptidases of five catalytic types accounted for ca. 8% and 6% of reliably identified proteins in PA and CA glands, respectively. Invadolysin, nardilysin, cathepsins B2 and L3, and elastase 2b orthologs were the major gland endopeptidases. Two cystatins and a serpin were highly abundant peptidase inhibitors in the glands. While PA glands generally had rich enzymatic equipment, CA glands were conspicuously abundant in venom allergen-like proteins.     

Bacterial Expression and Characterization of Functional Recombinant Triosephosphate Isomerase from Schistosoma japonicum

The dimeric enzyme triosephosphate isomerase (TPI) converts glyceraldehyde-3-phosphate to dehydroxyacetone phosphate, a key reaction in glycolysis. Previous studies of the native enzyme in the human bloodflukes belonging to the genus Schistosoma have indicated that TPI is a promising anti-schistosome vaccine antigen. However, a recombinant form of the enzyme is required as an alternative to the impractical option of using biochemically purified TPI obtained from worm tissue for large-scale vaccine use. We previously cloned and sequenced a full-length cDNA encoding the TPI of the Asian (Chinese strain) schistosome Schistosoma japonicum (SjcTPI). We now report very high level bacterial expression of this cDNA and the subsequent purification of the recombinant protein to >98% homogeneity under nondenaturing conditions. The recombinant SjcTPI (re-SjcTPI) was shown to be enzymatically active with a specific activity of 7687 units/mg protein, an activity higher than that of commercially obtained porcine TPI tested concurrently under the same assay conditions. The K_m value for the re-SjcTPI using glyceraldehyde-3-phosphate as substrate was 406.7 μM, which is similar to the K_m values reported for the yeast enzyme and various mammalian TPIs. With the availability of substantial amounts of enzymatically active and readily purified re-SjcTPI made in bacteria we can now test whether the recombinant protein can induce a similar level of protection in vaccination/challenge experiments as the native, biochemically purified enzyme.     

New genera and species of Leptophlebiidae (Ephemeroptera) from New Zealand

Abstract

New genera Isothraulus, Arachnocolus, and Penniketellus are established for three species of leptophlebiid mayfly from New Zealand. Each genus is monotypic and endemic to New Zealand. Isothraulus and Arachnocolus are known only from the northern North Island, and Penniketellus is known only from the Arthur's Pass area of the central South Island. The male and female imago, nymph, and egg of Isothraulus abditus n.sp., the male imago, male subimago, and nymph of Arachnocolus phillipsi n.sp., and the male and female imago, female subimago, and egg of Penniketellus insolitus n.sp. are described. The relationships of each genus and the ecology of nymphs of each species are discussed.     

Functional Expression of Dipeptidyl Peptidase I (Cathepsin C) of the Oriental Blood Fluke Schistosoma japonicum in Trichoplusia ni Insect Cells

Proenzyme dipeptidyl peptidase I (DPP I) of Schistosoma japonicum was expressed in a baculovirus expression system utilizing Trichoplusia ni BTI-5B1-4 (High Five) strain host insect cells. The recombinant enzyme was purified from cell culture supernatants by affinity chromatography on nickel–nitriloacetic acid resin, exploiting a polyhistidine tag fused to the COOH-terminus of the recombinant protease. The purified recombinant enzyme resolved in reducing SDS–PAGE gels as three forms, of 55, 39, and 38 kDa, all of which were reactive with antiserum raised against bacterially expressed S. japonicum DPP I. NH₂-terminal sequence analysis of the 55-kDa polypeptide revealed that it corresponded to residues −180 to −175, NH₂-SRXKXK, of the proregion peptide of S. japonicum DPP I. The 39- and 38-kDa polypeptides shared the NH₂-terminal sequence, LDXNQLY, corresponding to residues −73 to −67 of the proregion peptide and thus were generated by removal of 126 residues from the NH₂-terminus of the proenzyme. Following activation for 24 h at pH 7.0, 37°C under reducing conditions, the recombinant enzyme exhibited exopeptidase activity against synthetic peptidyl substrates diagnostic of DPP I. Specificity constants (k_cat/K_m) for the recombinant protease for the substrates H-Gly-Arg-NHMec and H-Gly-Phe-NHMec were found to be 14.4 and 10.7 mM⁻1 s⁻¹, respectively, at pH 7.0. Approximately 1 mg of affinity-purified schistosome DPP I was obtained per liter of insect cell culture supernatant, representing 2 × 10⁹ High Five cells.     

Structure of synthetic peptide analogues of an eggshell protein of Schistosoma mansoni.

The peptide (Gly-L-Tyr-L-Asp-L-Lys-L-Tyr)6, referred to as F4-6, was synthesized as a model for a schistosome eggshell protein in which the Gly-Tyr-Asp-Lys-Tyr consensus sequence is repeated over 40 times. Analysis by CD, Fourier transform infrared spectroscopy, potentiometric and spectrophotomertric titrations, NMR, and molecular modeling suggests that F4-6 forms some type of left-handed structure. A likely possibility appears to be a left-handed alpha-helix stabilized by Lysi-Aspi +4 salt bridges and possibly Aspi-Tyri +4 hydrogen bonding and Tyr-Tyr interactions. Spectroscopic studies of a number of F4-6 analogues support this conclusion. For example, substitution of D-Ala for Gly produces a peptide with enhanced left-handed helical spectral characteristics, whereas an L-Ala substitution results in a peptide with minimal structure. These studies suggest that the F4 protein from Schistosoma mansoni may be the first example of a naturally occurring protein devoid of proline and carbohydrate that forms a left-handed helix composed of L-amino acids, although alternative forms of other left-handed structures have yet to be rigorously excluded.