Identification of the major tRNA(Phe) binding domain in the tetrameric structure of cytoplasmic phenylalanyl-tRNA synthetase from baker's yeast

Native cytoplasmic phenylalanyl-tRNA synthetase from baker's yeast is a tetramer of the alpha 2 beta 2 type. On mild tryptic cleavage it gives rise to a modified alpha 2 beta 2 form that has lost the tRNA(Phe) binding capacity but is still able to activate phenylalanine. In this paper are presented data concerning peptides released by this limited proteolytic conversion as well as those arising from exhaustive tryptic digestion of the truncated beta subunit. Each purified peptide was unambiguously assigned to a unique stretch of the beta subunit amino acid sequence that was recently determined via gene cloning and DNA sequencing. Together with earlier results from affinity labelling studies the present data show that the Lys 172-Ile 173 bond is the unique target of trypsin under mild conditions and that the N-terminal domain of each beta subunit (residues 1-172) contains the major tRNA(Phe) binding sites.     

Oligotrophication as a result of planktivorous fish removal with rotenone in the small,eutrophic, Lake Mosvatn,Norway

In September 1987 the shallow, eutrophic, Lake Mosvatn was treated with rotenone to eliminate planktivorous fish (mainly whitefish,Coregonus lavaretus, L.), and the effects were studied. The first summer after treatment the zooplankton community changed markedly from rotifer dominance and few grazers, to a community with few rotifers and many grazers. Accordingly there was a fivefold increase in the biomass ofDaphnia galeata. Adult females ofD. galeata approximately doubled in weight. The decrease in rotifer biomass was probably mainly due to a loss of food by competition with the daphnids. The phytoplankton community was also markedly affected. Prior to treatment Secchi depth was 1.7 m and Chl-a 23μg l⁻¹ in the summer. After treatment there was an increase in the proportion of small and gelatinous algae and the mean chlorophyll concentration fell to 7μg Chl-a l⁻¹. Secchi depth increased to>2.3 m (bottom-sight most of the season). After the treatment there were also fewer cyanobacterial blooms. This seems to be related to oligotrophication caused indirectly by increased grazing by the zooplankton. Total nutrient concentrations were affected. Prior to treatment the mean summer concentration of total phosphate was 44μg P l⁻¹. This decreased to 29μg P l⁻¹ in the first summer and 23μg P l⁻¹ the second summer after the treatment. Total nitrogen decreased from 0.68 mg N l⁻¹ before treatment to 0.32 mg N l⁻¹ the first summer after the treatment. The phosphate loading was not reduced, therefor it can be concluded that the fish removal provided a biomanipulation which caused the more oligotrophic conditions.     

Responses of algae, bacteria, Daphnia and natural parasite fauna of Daphnia to nutrient enrichment in mesocosms

Understanding responses of parasites to changes in nutrient regimes is necessary for prediction of their role in aquatic ecosystems under global change in nutrient loading. We studied the response of the natural parasite fauna of Daphnia longispina to nutrient enrichment in mesocosms in a small humic lake. We measured the concentrations of inorganic phosphorus and nitrogen in the water, total nutrients in the seston, algal and bacterial biomass, Daphnia population dynamics, Daphnia stoichiometry, Daphnia stable isotope values and the presence and abundance of parasites in treated mesocosms as compared to three control ones. Incorporation of the nutrient enrichment in the food web was seen as increased nutrient concentrations in the epilimnion and as a decrease in carbon:nutrient ratios and δ¹⁵N values in Daphnia. Nutrient enrichment did not significantly influence algal, bacterial or Daphnia biomass. One of the four parasite species observed, unidentified small gut parasite, had a higher prevalence (percentage of Daphnia infected) in treated mesocosms, but its intensity (number of parasites per infected host) remained the same among treatments. Our results suggest that the effect of nutrient enrichment on host–parasite dynamics is dependent on complex interactions within food webs and on the epidemiological traits of parasites.     

Parasite infection alters host stable‐isotope composition under controlled feeding

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The role of cerebral oedema in the pathogenesis of cerebral malaria

It has been suggested that sequestration of parasitized red blood cells might contribute to the pathogenesis of cerebral malaria (CM), by hypoxia causing either: (i) compensatory vasodilatation with a resultant increase in the brain volume; or (ii) enhancing cytokine-induced nitric oxide (NO) production via induction of inducible NO synthase (iNOS). Available evidence suggests that cerebral oedema is the initiating and probably the most important factor in the pathogenesis of murine CM. The relevance of this model in the study of the pathogenesis of CM has been questioned. However, a closer look at published reports on both human and murine CM, in this review, suggests that the pathogenesis of the murine model of CM might reflect more closely the CM seen in African children than that seen in Asian adults. It is also proposed that the role of iNOS induction during CM is protective: that the primary purpose of iNOS induction is to inhibit the side effects of brain indoleamine 2,3-dioxygenase (IDO) induction and quinolinic acid accumulation during hypoxia.     

Biodegradation of radiolabelled synthetic lignin (14C-DHP) and mechanical pulp in a compost environment

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Simultaneous determination of m-nisoldipine and its three metabolites in rat plasma by liquid chromatography–mass spectrometry

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Plant growth-promoting rhizobacteria do not pose any deleterious effect on cowpea and detectable amounts of ethylene are produced

Summary The use of trap crops such as cowpea could reduce the effects of the root parasitic weed, Striga hermonthica and its subsequent constraints on the growth of cereals. Certain bacteria could augment the trap crop stimulatory effect. We studied the effect of three bacteria introduced to the rhizosphere of three cowpea varieties at planting. Number of days to cowpea flowering was noted and at harvest, data were collected on pod characteristics and biomass. Means of data subjected to ANOVA were compared using Tukey’s Studentized Range Test. We analysed bacterial headspace volatiles for ethylene by gas chromatography and gas chromatography–mass spectrometry. Bacterial type significantly influenced the cowpea varieties with better performance over the non-inoculated control. Average pod weight (g) with bacterial treatment was 37.97 for Enterobacter sakazakii 8MR5, 34.38 for Pseudomonas 44MS8 and 27.46 for Pseudomonas 10M3. Non-inoculated control had an average weight of 20.98 g. Bacteria promoted a significant increase in pod weight (≥30.89%), fresh biomass (≥24.22%), and improved pod number (≥20.54%) and pod wall thickness (≥7.33%) with no deleterious effect on plant health. Ethylene released by the bacteria ranged from trace concentrations in Pseudomonas sp. to 210 nmoles/10⁸ c. f. u./ml in Ent. sakazakii 8MR5.     

The role of organic matter and microbial community controlling nitrate reduction under elevated ferrous iron concentrations in boreal lake sediments

Hydrobiologia - The nitrogen availability, that affects the greenhouse gas emission and the trophic level of lakes, is controlled mainly by microbial processes. We measured in a boreal nitrate and...