Assimilation of E. coli cells by Daphnia magna on the whole organism level

Consumption of E. coli cells by Daphnia magna was studied. It was found that this organism not only ingested E. coli cells but digested them as demonstrated by the release of ¹⁴CO₂ originating from E. coli grown on ¹⁴C-glucose, and by the transfer of the radioactive label from parental Daphnia to their progenies. In addition the effect of antibiotics on the consumption of E. coli cells by Daphnia magna was studied. In long incubation times, antibiotics inhibited bacterial uptake by Daphnia. The microflora isolated from Daphnia was found to be capable of causing leakage of enzymes out of E. coli cells thus playing at least a partial role in the digestion of E. coli cells by Daphnia.     

Ability of Daphnia Cell-Free Extract to Damage Escherichia coli Cells

A cell-free extract of Daphnia magna was found to lyse Escherichia coli cells as shown by leakage of the enzymes alkaline phosphatase and β-galactosidase from the bacteria. The cell-free extract was separated on Sephadex G-200, and the fractions showing an ability to lyse E. coli cels were isolated. The factor which was responsible for the lysis of the bacterial cells was probably a protein with a molecular weight of several thousands. Mg²⁺ and Ca²⁺ ions augmented the activity of the Daphnia extract on E. coli cells.     

Nitrate reductase activity,ammonium regeneration,and orthophosphate uptake in protozoa isolated from Lake Kinneret,Israel

Nitrate reductase (NR) activity and nutrient (N, P) recycling in the ciliatesColpoda steinii andStylonychia sp. and two unidentified flagellates (I and II), isolated from Lake Kinneret, have been studied. When grown on a bacterium also isolated from the lake, all species, except flagellate I, exhibited NR activity. Activity was higher in the presence of nitrate than in its absence, and in the case ofC. steinii showed a dependence on initial ambient NO₃ concentrations in the cultures. NR activity was inversely proportional to body size, suggesting that the larger protozoan species have decreased specific metabolic rates. A net increase in ammonium concentrations and a decrease in orthophosphate levels was observed, but both phenomena were much less sensitive to ambient NO₃ concentrations than NR activity. Similar trends in NR activity and NH₄ production were also observed whenC. steinii was grown on the picocyanobacteriumSynechococcus sp. Our results suggest that NH₄ excretion is the outcome of N remineralization from the food supply but is also partially due to dissimilatory nitrate reduction. These data imply that protozoa may have an important role in nutrient recycling in Lake Kinneret and that some species could use NO₃ respiration in anoxic regions of the water column. Offprint requests to: O. Hadas.     

Sulfte-reduction process in sediments of Lake Kinneret,Israel

Monomictic Lake Kinneret is stratified during summer and autumn, resulting in a hypolimnion rich in H₂S (3–7 mg 1^–1). In winter and spring every year a bloom of dinoflagallate Peridinium gatunense produces an average biomass of 150000 ton wet weight. Part of this biomass sinks to the hypolimnion and sediments where it is decomposed and mineralized, with some of the mineralization due to the activity of sulfate-reducing bacteria (SRB). The sulfate-reduction potential of the upper sediment layer at the deepest part of the lake (42 m) was measured. The activity of the enzyme arylsulfatase was also monitored. Rates of sulfate-reduction ranged from a minimum of 12 nmoles SO_f4 ^p2–-reduced cm^–3 day^–1 in December before lake overturn to a maximum of 1673 nmoles SO_f4 ^p2– reduced cm^–3 day^–1 in July during stratification. These rates are considerably higher than those recorded from other freshwater lakes in the world and are probably limited more by the availability of organic matter than by sulfate concentrations.     

Partition of free and monoclonal-antibody-bound horseradish peroxidase in a two-phase aqueous polymer system--novel procedure for the determination of the apparent binding constant of monoclonal antibody to horseradish peroxidase.

The principle that the antigen and the antibody prefer different phases in an aqueous two-phase system is the analytical basis of the work presented here. The antigen horseradish peroxidase, which is bound to a monoclonal antibody (mAb), is separated from free Ag in an aqueous phase system (polyethylene glycol (PEG)/dextran) as a function of the concentration of mAb. The plot of the partition coefficient kappa of horseradish peroxidase versus the concentration of mAb yields a sigmoidal curve similar to the curve obtained by enzyme-linked immunosorbent assay (ELISA). Comparing the plots normally used for ELISA in order to determine the apparent binding constant of mAb and the number of epitopes on the Ag we derived a relationship between the difference in partitioning of the free Ag and the bound Ag (delta kappa) and the concentration of mAb. The new linear plot of reciprocal delta kappa versus reciprocal concentration of mAb gives the apparent binding constant of mAb, which is evaluated from the slope. From the intercept at the ordinate the maximum difference of the partition coefficient of the free and bound antigen is derived and the apparent partition coefficient of the free monoclonal antibody can be calculated.     

High abundance of picoplankton-ingesting ciliates during late fall in Lake Kinneret, Israel

Small, aloricate ciliates dominated the biomass of heterotrophicprotists throughout the water column at the end of the periodof stratification in Lake Kinneret, Israel The integrated biomassof cilates was 5–20 times that of heterotrophic flagellatesDuring incubation experiments, ciliate growth rates in cpilimneticwater corresponded to population doubling times of 9.6–19.4h, while flagellate populations showed no growth. Most of thealiates were small forms (10–30 µm long), includingscuticocihates, choreotnchs, Coleps spp. and Colpoda spp., andappeared to be consuming bacteria, coccoid cyanobacteria, and<5 µm eukaryotic algae. Grazing rates of cihate assemblageson picoplankton in the epilimnion, as determined by the uptakeof fluorescently labeled bacteria and cyanobactena, ranged from62 to 86 nl cell^–1 h^–1 Colpoda steini, isolatedfrom lakewater, grew on a cultured freshwater Synechococcussp with a doubling time of 4.5 h, and a gross growth efficiencyof 48% The estimated daily requirements of ciliates for growthapproximately equalled total phytoplankton production. We calculatedthat ciliates in the epilimnion were clearing 4–10% ofthe bacterioplankton and cyanobactenal standing stocks per daySince this would not be sufficient food consumption to meetdaily carbon requirements of the aliates, it is likely thatthese organisms were also grazing a significant amount of autotrophicand heterotrophic eukaryotic cells in Lake Kinneret.     

Antibodies to a soluble form of a tumor necrosis factor (TNF) receptor have TNF-like activity.

Immunological cross-reactivity between tumor necrosis factor (TNF) binding proteins which are present in human urine (designated TBPI and TBPII) and two molecular species of the cell surface receptors for TNF is demonstrated. The two TNF receptors are shown to be immunologically distinct, to differ in molecular weight (58,000 and 73,000), and to be expressed differentially in different cells. It is further shown that polyclonal antibodies against one of the TNF binding proteins (TBPI) display, by virtue of their ability to bind the TNF receptor, activities which are very similar to those of TNF. These antibodies are cytotoxic to cells which are sensitive to TNF toxicity, induce resistance to TNF toxicity, enhance the incorporation of thymidine into normal fibroblasts, inhibit the growth of chlamydiae, and induce the synthesis of prostaglandin E2. Monovalent F(ab) fragments of the polyclonal antibodies lack TNF-like activities, but acquire them upon cross-linking with anti-F(ab)2 antibodies, suggesting that the ability of the anti-TBPI antibodies to mimic TNF correlates with their ability to cross-link the TNF receptors. This notion was further supported by data obtained in a comparative study of the TNF-like cytotoxicity of a panel of monoclonal antibodies against TBPI. The induction of TNF-like effects by antibodies to a TNF receptor suggests that TNF is not directly involved in intracellular signalling. Rather, it is the receptors to this cytokine which, when properly triggered in a process which appears to involve clustering of these receptors, transduce the signal for response to TNF into the cell's interior.     

Characterization of secretory leukocyte protease inhibitor as an inhibitor of implantation serine proteinases

We have recently identified and characterized two implantation serine proteinase genes, ISP1 and ISP2, which give rise to a dimeric proteinase, ISP that facilitates embryo invasion during peri-implantation period. As many proteinases have cognate serpins that regulate their proteolytic activity, we have been investigating anti-tryptases, expressed during this window of implantation. Here, we report the differential expression of secretory leukocyte protease inhibitor (SLPI) in uterine endometrium around the implantation period. The co-localization of SLPI and ISP suggests the possibility that SLPI is an ISP serpin and that expression of SLPI may lead to a reduction in ISP activity. The expression of SLPI is down regulated during the window of embryo-uterine receptivity. Our results are consistent with a model suggesting that the drop in SLPI expression may help to refine the opening of the window of implantation, by allowing the proteolytic activity of embryo invasive serine proteinases such as the ISPs.     

Effects of food abundance, age, and flea infestation on the body condition and immunological variables of a rodent host, and their consequences for flea survival

Temporal variation in body condition and immunological variables of animals that harbor parasites may explain patterns of variation in infestation, as well as parasite impact on the host. We emulated such variability in Sundevall's jirds by manipulating food availability and flea infestation in juveniles and adults and examining how these changes affect survival of fleas on their hosts. Body condition of food-restricted jirds deteriorated, but there was no change in their immunological variables. Adult jirds were in better body condition and had higher immunocompetence than juveniles, however there were no significant effects of flea infestation on any of the variables examined. The main effects of flea infestation were a decrease in the response to phytohaemagglutinin injection, and an increase in the negative effects of food restriction on body mass. Flea survival was higher on juveniles, but fleas did not respond to temporal variability in body condition and immunocompetence of the jirds. We concluded that changes in body condition and immune responses due to growth or variability in food abundance are more important than changes caused by the fleas themselves. Flea infestation is more detrimental to jirds when they are not able to compensate for mass loss through increased food consumption.