Vaccinia virus encodes a type I DNA topoisomerase that is highly conserved in all known poxviruses. Although the structure and catalytic activity of the enzyme were well studied, little was known about its biological function. The viral topoisomerase was thought to be essential, and roles in DNA replication, recombination, concatemer resolution, and transcription were suggested. Here, we demonstrated that the topoisomerase is not essential for replication of vaccinia virus in cultured cells, although deletion mutants formed fewer and smaller plaques on cell monolayers than wild-type virus. Purified mutant virus particles were able to bind and enter cells but exhibited reduced viral early transcription and a delay in DNA replication. Infecting with a high number of virus particles increased early mRNA and accelerated viral DNA synthesis. Processing of viral DNA concatemers into unit-length genomes was unimpaired at either a low or high multiplicity of infection. The data suggest that the primary, perhaps only, role of the poxvirus topoisomerase is to increase early transcription, which takes place within virus cores in the cytoplasm of infected cells. Because the topoisomerase functions early in infection, drugs capable of penetrating the virus core and irreversibly damaging DNA by trapping nicked DNA-topoisomerase intermediates could make potent antiviral agents.
BackgroundThe complex network of direct and indirect relationships determines not only the species abundances but also the community characteristics such as diversity and stability. In this context, seed predation is a direct interaction that affects the reproductive success of the plant. For Acrocomia aculeata, the seed predation by Pachymerus cardo and Speciomerus revoili in post-dispersal may destroy more than 70% of the propagules and is influenced by the herbivory of the fruits during pre-dispersal. Fruits of plants with a higher level of herbivory during pre-dispersal are less attacked by predators in post-dispersal. We proposed a hypothesis that describes this interaction as an indirect defense mediated by fungi in a multitrophic interaction. As explanations, we proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator.Methodology/Principal FindingsFor prediction (i), differences in the fungal colonization in fruits with an intact or damaged epicarp were evaluated in fruits exposed in the field. For prediction (ii), we performed fruit observations in the field to determine the number of eggs of P. cardo and/or S. revoili per fruit and the amount of fungal colonization in the fruits. In another experiment, in the laboratory, we use P. cardo females in a triple-choice protocol. Each insect to choose one of the three options: healthy fruits, fruits with fungus, or an empty pot. The proposed hypothesis was corroborated. Fruits with injuries in the epicarp had a higher fungal colonization, and fruits colonized by fungi were less attractive for egg-laying by seed predators.Conclusion/SignificanceThis study emphasizes the importance of exploring the networks of interactions between multitrophic systems to understand the dynamics and maintenance of natural populations.
RESUMO.-[Atividade antimicrobiana, toxicidade aguda e crônica do óleo essencial de Lippia origanoides.]Atualmente nota-se um aumento do interesse pelas plantas medicinais, fruto da grande procura por terapias alternativas. Neste trabalho foi avaliada a atividade antimicrobiana e a toxicidade do óleo essencial da Lippia origanoides (alecrim-pimenta). O óleo essencial de alecrim-pimenta foi obtido por arraste com vapor d'água e seus constituintes foram identificados por cromatografia acoplada a espectrofotômetro de massa (GC/MS). Entre os 15 compostos identificados os mais abundantes foram o carvacrol (29%), o-cimeno (25,57%) e metil timol éter (11,50%). Os óleos foram submetidos a ensaios antimicrobianos para determinação da CIM e da CBM. Os resultados mostraram que a dose de 120μl/mL de qualquer um dos óleos testados foi eficiente em inibir o crescimento dos micro-organismos Escherichia coli (ATCC 25922) Currently, there is a growing interest in medicinal plants, because of an increased demand for alternate therapies. In this study, the antimicrobial activity and toxicity of the essential oil of Lippia origanoides (L. origanoides) were investigated. The essential oil of L. origanoides was extracted by steam-dragging distillation and its constituents were identified by chromatography coupled with mass spectrometry. Among the 15 compounds identified, the most abundant were carvacrol (29.00%), o-cymene (25.57%), and thymol methyl ether (11.50%). The essential oil was studied in antimicrobial assays to determine the MIC and MBC. The results indicated that a concentration of 120μL/mL of oil was sufficient to inhibit the growth of the following microorganisms: Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923) and Salmonella cholerasuis (ATCC 10708). Acute and chronic toxic effects of orally administered oil were investigated in Wistar rats by using standard methods. Doses of 30, 60 and 120mg/kg of the essential oil did not induce significant changes in weight, behavior or hematological and biochemical parameters in the animals. There were no signs of any histopathological changes to the liver, kidneys or heart of the treated rats, suggesting that Lippia origanoides oil is non--toxic after oral administration in acute or chronic toxicity studies. The results obtained in this study show that the essential oil of L. origanoides has a high safety margin, with no detectable toxic effects in rats treated with doses to 120mg/kg. In addition, L. origanoides oil demonstrated potent antimicrobial activity against S. aureus, E. coli and S. cholerasuis. Based on these findings, this essential oil may have practical application as a veterinary antimicrobial.INDEX TERMS: Lippia origanoides, essential oil, antimicrobial, acute toxicity, chronic toxicity.
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