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 $\delta \approx -1$ close to their centers to $\delta \approx 0$ close to their boundaries. We present an analysis of the level of distinction between GR and two modified gravity theories, the Hu-Sawicki $f(R)$ 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 $\overline\rho_v=0.2\,\overline\rho_m$, 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 $|f_{R0}| > 10^{-6}$ and $z_{SSB} > 1$. 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”

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