Characterization of the Melanogenic System in Vibrio cholerae,ATCC 14035

The nature of the pigment formed by Vibrio cholerae and the characterization of its biosynthetic pathway is shown. This microorganism is able to synthesize melanin-like pigment when cultured in the presence of L-tyrosine. Other phenolic chemicals related to L-tyrosine do not lead to pigment production. The microorganism has no tyrosine hydroxylase activity, and the levels of dopa oxidase activity are very low, making the existence of a tyrosinase very unlikely. However, Vibrio cholerae contained transami-nases that transforms L-tyrosine into p-hydroxyphenylpyruvate. Moreover, Vibrio cholerae is able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously be oxidized to its p-quinone form, which subsequently polymerizes leading to pigment formation. It is concluded that the pigment formed by Vibrio cholerae is not synthesized by the Raper-Mason pathway, but by a L-tyrosine catabolism pathway leading to homogentisic acid. Some simple properties of that melanin are compared to model eu- and pheomelanin, but no clear distinction could be stated, indicating the similarity between all these pigments.     

The Different Behavior of Diphtheria Toxin, Modeccin and Ricin in HeLa Cells Infected with Trypanosoma cruzi

ABSTRACT. We have studied the action of diphtheria toxin, modeccin and ricin on HeLa cells infected by Trypanosoma cruzi . Parasitized HeLa cells were resistant to diphtheria toxin and modeccin, whereas non-parasitized cells from the same cultures and control cultures showed cytopathological alterations. Protein synthesis, assayed by the incorporation of labelled methionine, diminished in toxin-treated control cultures but remained unaltered in the infected ones, compared to synthesis by untreated infected cells. Ricin, on the other hand, is a toxin that enters the cytoplasm by endocytosis. It has greater cytopathological effects in parasitized cells than in non-parasitized ones from the same cultures or uninfected control cells. Protein synthesis was inhibited in infected cultures treated with ricin.     

Teratoid Tumors Derived from Mouse Embryos Grown in an Immunologically Privileged Site

Mouse early embryos and embryo fragments were transplanted into an immunologically privileged site, consisting of a glass cylinder previously implanted under the skin of adult mice in order to test their tumor producing potential, in allogeneic adult recipients. The highest yield of tumors was obtained upon transplantation of 6 1/2 day old embryos in toto. i.e., including the embryonic and extraembryonic areas. Histological examination showed teratomas composed of differentiated tissues derived from the three germ layers containing isolated foci of undifferentiated cells and nodules of trophoblast giant cells. Areas exhibiting the histological appearance of yolk sac carcinoma were also observed. Transplantation of the whole 6 1/2 day old egg cylinder, including the ectoplacental cone, and the isolated embryonic area produced a lower incidence of teratomas with a reduced variety of differentiated tissues. No yolk sac carcinoma was found in these grafts. The ectoplacental cone of 6 1/2 day embryos produced no tumors. Grafts of genital ridges from 12 1/2 day embryos gave rise to teratomas with well differentiated tissues of embryonic and extraembryonic origin. Areas ressembling yolk sac carcinoma were also observed. The life span of trophoblastic giant cells within the glass cylinder was significantly longer than in other experimental systems.     

Between‐year variations in Little Bustard Tetrax tetrax population densities are influenced by agricultural intensification and rainfall

The Little Bustard is suffering a widespread population decline mainly due to agricultural intensification. This study evaluates the effects of intensification level, habitat availability and rainfall on the population dynamics of this species. The population density of males was monitored for 7 years (2002–2008) at 184 points located within three sites with contrasting levels of agricultural intensification in southern Portugal. Densities decreased along the intensification gradient from 8.2 to 2.3 males / km². Overall, there was an approximately 50% population decline during the period 2002–2008, driven by a decline observed in one of the less intensive sites, whereas in the other two sites densities remained fairly constant. Yearly variations in male densities were influenced by intensification level, amount of grassland habitat and rainfall patterns. Thus, agricultural intensification is having a negative effect on population densities of this threatened species, particularly through the loss of grasslands (fallow fields and pastures) suitable for displaying males. The results also suggest a positive impact of rainfall on male densities, although this is more likely in grasslands within less intensive agricultural regions of poorer soil quality, where higher breeding male densities occur. Grassland habitat quality, driven by both climate and human management, probably plays a major role in the population dynamics of this threatened steppe bird in its strongholds.     

Ecological factors influencing disease risk in Eagle Owls Bubo bubo

In this study we assessed whether local habitat features and host population density influenced disease risk in Eagle Owl Bubo bubo fledglings. Measures of immune defence (concentrations of circulating white blood cells), prevalence of three parasite types (a blood parasite Leucocytozoon ziemanni , an insect Carnus haemapterus , and a tick Rhipicephalus sp.) and total number of parasite species were used to quantify disease risk. We tested the hypotheses that disease risk in fledglings was higher in nests located in areas with higher length of and proximity to watercourses (as a higher abundance and viability of parasites and vectors occur in wetter areas), higher cover of forest (as forest moistness and humidity can favour higher vector and parasite proliferation), higher habitat diversity (as environmental heterogeneity increases the pool of potential vectors and parasites) and higher local owl population density (as disease transmission might be density-dependent). The clearest relationship was with the proximity of freshwater, although the other hypotheses were also partially supported. Concentrations of white blood cells, the number of parasite species and, weakly, the prevalence of Carnus haemapterus were all higher in nests closer to watercourses. The prevalence of blood parasites increased with the cover of forested areas. Fledglings from nests located in more diverse habitats had higher white blood cell concentrations and showed higher prevalence of blood parasites. Finally, local host population density was positively correlated with the prevalence of blood parasites. The results suggest the existence of complex and interrelated links between ecological parameters and three different measures of disease risk, and highlight the importance of immunological approaches to assess disease risk at an intraspecific level.     

Effects of omnivorous filter‐feeding fish and nutrient enrichment on the plankton community and water transparency of a tropical reservoir

1. The major aim of this study was to test the hypothesis that nutrient enrichment and the introduction of the Nile tilapia (Oreochromis niloticus), an exotic omnivorous filter‐feeding fish, operate interdependently to regulate plankton communities and water transparency of a tropical reservoir in the semi‐arid northeastern Brazil. 2. A field experiment was performed for 5 weeks in 20 enclosures (9.8 m³) to which four treatments were randomly allocated: tilapia addition (F), nutrient addition (N), tilapia and nutrient addition (F + N) and a control treatment with no tilapia or nutrient addition (C). A two‐way repeated measures anova was undertaken to test for time, tilapia and nutrient effects and their interactions on water transparency, total phosphorus and total nitrogen concentrations, phytoplankton biovolume and zooplankton biomass. 3. Nutrient addition had no effect except on rotifer biomass, but there were significant fish effects on the biomass of total zooplankton, copepod nauplii, rotifers, cladocerans and calanoid copepods and on the biovolume of total phytoplankton, large algae (GALD ≥ 50 μm), Bacillariophyta and Zygnemaphyceae and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased water transparency, while nutrient enrichment increased the biomass of rotifers, but only in the absence of tilapia. 4. In conclusion, the influence of fish on the reservoir plankton community and water transparency was significant and even greater than that of nutrient loading. This suggests that biomanipulation of filter‐feeding tilapias may be of importance for water quality management of eutrophic reservoirs in tropical semi‐arid regions.