2,666 research outputs found
Fungal protoplasts as a genetic tool
For the last three decades, protoplasts have been shown to be an effective tool in
studying the biochemistry and genetics of fungi, as the thick cell wall is no more a
barrier. In this work we describe and discuss this versatile tool in mycology in two
ways, preparation level and utilisation level. At the preparation level we describe the optimal conditions to obtain yeast protoplasts,
including buffers employed, incubation time, regeneration of protoplasts, and compare
the methodology to obtain the protoplasts from yeast and filamentous fungi. At the
utilisation level we analyse the methodology to introduce foreign DNA into host
genomes via protoplast transformation, probably the most universal method of gene
transfer, and via protoplast fusion, a tool to "illegitimaly" transfer nuclear and/or
organellar genetic information beyond phylogenetic boundaries. Finally, we conclude
about the importance and actuality of fungal protoplasts in mycological research
Cosmic voids in modified gravity scenarios
Modified gravity (MG) theories aim to reproduce the observed acceleration of
the Universe by reducing the dark sector while simultaneously recovering
General Relativity (GR) within dense environments. Void studies appear to be a
suitable scenario to search for imprints of alternative gravity models on
cosmological scales. Voids cover an interesting range of density scales where
screening mechanisms fade out, which reaches from a density contrast close to their centers to close to their
boundaries. We present an analysis of the level of distinction between GR and
two modified gravity theories, the Hu-Sawicki and the symmetron theory.
This study relies on the abundance, linear bias, and density profile of voids
detected in n-body cosmological simulations. We define voids as connected
regions made up of the union of spheres with a {\it \textup{mean}} density
given by , but disconnected from any
other voids. We find that the height of void walls is considerably affected by
the gravitational theory, such that it increases for stronger gravity
modifications. Finally, we show that at the level of dark matter n-body
simulations, our constraints allow us to distinguish between GR and MG models
with and . Differences of best-fit values for
MG parameters that are derived independently from multiple void probes may
indicate an incorrect MG model. This serves as an important consistency check.Comment: 15 pages, 12 figure
Extração de nemátodes de quisto de amostras de solo: método de decantação e crivagem de Cobb vs. método de Fenwick
Potato cyst nematodes are a threat to several agricultural crops around the world with some species considered quarantine
pests and subjected to strict regulatory measures in many countries. Usually, cysts nematodes co-exist in the soil
with other species of plant-parasitic nematodes, so, a time and cost-efficient extraction technique becomes of primary
importance. The ideal extraction method should be able to obtain cysts as well as detecting the presence of other motile
plant-parasitic nematodes with a potential impact on potato farming (such as Meloidogyne sp. and Pratylenchus sp.). In
recent years, studies have been carried out to test the efficiency of various methods of nematode extraction but few
results have been published. Therefore, to test if a method that extracts simultaneously cysts and motile nematodes
can be used instead of the reference method that extracts cysts only, the efficiency of Cobb’s decanting and sieving
technique was compared to Fenwick’s technique. As a result, in the 74 samples evaluated, a greater number of cysts
were extracted from 24 samples using Fenwick’s method and from 11 samples employing Cobb’s decanting and sieving
technique. The statistics results showed a significance level of 0,05 using Fenwick’s can allowing to conclude that this
method is much more efficient than Cobb’s decanting and sieving technique, and confirming it should not be replaced
by alternative methods for cysts extractioninfo:eu-repo/semantics/publishedVersio
Name your own change : the success history of Priceline.com
The Dynamic Capabilities View emerged from the work of several researchers, aiming to
provide an explanation for a firm’s success in a fast-changing environment. This Thesis
strives for the analysis of the Dynamic Capabilities literature through the real life business
history of Priceline.com, an online travel agency founded in United States. The case shows
that the company has a high propensity to sense opportunities and threats, to make
market oriented decisions and to change their resources base while having a medium
propensity to make timely decisions. In addition, evidence suggests that dynamic
capabilities were key for the Priceline.com's success within a fast-changing environment,
giving support to the literature that defines Dynamic Capabilities as the “firm’s potential to
systematically solve problems”
Tratamento cirúrgico simultâneo da comunicação oroantral e da sinusite maxilar odontogénica-revisão bibliográfica
Physiological responses of Tetrahymena pyriformis to copper, zinc, cycloheximide and Triton X-100
Protozoa, and particularly ciliates, are essential in aerobic purification processes of wastewaters and have proved to be very
sensitive to environmental changes. The physiological response of the ciliate Tetrahymena pyriformis was assessed in terms of
mortality, growth and grazing capacity after exposure to four toxicants: copper, zinc, cycloheximide and Triton X-100. In the
ranges of concentrations used, mortality, inhibition of growth and inhibition of grazing were observed with all toxicants
employed, but in different ways. Copper and zinc showed lower toxicity than observed in other studies with protozoa, though
some of the present results are in accordance with those reported by other authors. This supports the importance of the
organism tested and the experimental conditions of the bioassays.Instituto de Biotecnologia e Química Fina (IBQF).Fundação para a Ciência e a Tecnologia (FCT) - Praxis XXI - 2/2.1/BIO/1118/95, Praxis XXI - grant BD/5080/95
Mutagenesis and transformation of Aspergillus terreus based on the nitrate reductase pathway
Aspergillus terreus is an efficient producer of different extracellular enzymes
which are used in food industries. Thus, we are interested in developing a
genetic transformation system based on the nitrate structural gene niaD. In
order to develop this system the nitrate assimilation pathway in A. terreus was
studied and spontaneous mutants defective in the genes required for nitrate
assimilation were obtained on the basis of chlorate resistance. Of particular
interest were niaD mutants which failed to grow on nitrate but grew as wild type
on other sole nitrogen sources.
Afterwards the transformation system was developed for mutants defective in
nitrate reductase of A. terreus using pSTA10 vector containing niaD gene from
A. niger. The transformation frequency obtained was c.a. 0.5 per ug DNA. The
vector appeared to be mitotically stable and Southern hybridization analysis of
transformants showed that transformation events occurred by integration into to
the recipient genome. To assess the amount of product made by the
transformants, nitrate reductase assays were carried out under inducing
conditions.
Experiments to improved transformation frequency and to characterize the
integration are now in progress
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