Dispersão de argilas em solos afetados por sais

Para estimar a dispersão de argilas determina-se, em laboratório, a argila dispersa em água. Esta análise pode não corresponder à realidade em solos salinos e salino-sódicos com concentrações elevadas de sais na sua solução. Neste contexto determinou-se a argila dispersa utilizando soluções de diferentes condutividades elétricas (0; 0,3; 0,6, 0,9 e 1,2 dS m-1) em sete solos representativos do Estado de Pernambuco com percentagem de saturação de sódio ajustada no intervalo de 5-30%. Os resultados evidenciaram que houve incremento nos valores da argila dispersa diretamente relacionado com o aumento da percentagem de saturação de sódio e com a diminuição da condutividade elétrica na solução de trabalho. A resposta aos tratamentos foi mais acentuada nos solos com maiores proporções de argilas mais ativas frente àqueles com mais óxidos de ferro. As determinações da argila dispersa em água são realizadas com água deionizada ou destilada; no entanto concluiu-se, para solos afetados por sais, que as análises deveriam ser realizadas com soluções de condutividade elétrica diferente de 0 dS m-1, utilizando-se valores próximos aos do extrato da pasta de saturação

Phylogenetic analysis reveals a high level of speciation in the Paracoccidioides genus

Paracoccidioidomycosis (PCM) is a systemic disease endemic to most of Latin America, with greatest impact in rural areas. The taxonomic status of one of the best studied Paracoccidioides isolates (Pb01) as A brasiliensis remains unresolved due to its genomic differences from the other three previously described phylogenetic species (S1, PS2 and PS3; Carrero et al., 2008. Fungal Genet. Biol. 45, 605). Using the genealogic concordance method of phylogenetic species recognition (GCPSR) via maximum parsimony and Bayesian analysis, we identified a clade of 17 genotypically similar isolates, including Pb01, which are distinct from the S1/PS2/P3 clade. Consistent with GCPSR, this "Pb01-like" group can be considered a new phylogenetic species, since it is strongly supported by all independent and concatenated genealogies. "Pb01-like" species exhibit great sequence and morphological divergence from the S1/PS2/PS3 species clade, and we estimate that these groups last shared a common ancestor approximately 32 million years ago. In addition, recombination analysis revealed independent events inside both main groups suggesting reproductive isolation. Consequently, we recommend the formal description of the "Pb01-like" cluster as the new species Paracoccidioides lutzii, a tribute to Adolpho Lutz, discoverer of P. brasiliensis in 1908. (C) 2009 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

<i>C</i>. <i>neoformans</i> autophagy-related genes respond to lack of nitrogen at the permissive temperature (30°C).

<p>Fifteen of twenty-one genes tested had an increase in their expression pattern above two-fold when the yeast cells were subjected to nitrogen starvation. All fold values were calculated from triplicate assays and were statistically validated by ANOVA (p< 0.05).</p

The role of Aspartyl aminopeptidase (Ape4) in <i>Cryptococcus neoformans</i> virulence and authophagy

<div><p>In order to survive and cause disease, microbial pathogens must be able to proliferate at the temperature of their infected host. We identified novel microbial features associated with thermotolerance in the opportunistic fungal pathogen <i>Cryptococcus neoformans</i> using a random insertional mutagenesis strategy, screening for mutants with defective growth at 37^°C. Among several thermosensitive mutants, we identified one bearing a disruption in a gene predicted to encode the Ape4 aspartyl aminopeptidase protein. Ape4 metalloproteases in other fungi, including <i>Saccharomyces cerevisiae</i>, are activated by nitrogen starvation, and they are required for autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway. However, none have been previously associated with altered growth at elevated temperatures. We demonstrated that the <i>C</i>. <i>neoformans ape4</i> mutant does not grow at 37°C, and it also has defects in the expression of important virulence factors such as phospholipase production and capsule formation. <i>C</i>. <i>neoformans</i> Ape4 activity was required for this facultative intracellular pathogen to survive within macrophages, as well as for virulence in an animal model of cryptococcal infection. Similar to <i>S</i>. <i>cerevisiae</i> Ape4, the <i>C</i>. <i>neoformans</i> GFP-Ape4 fusion protein co-localized with intracytoplasmic vesicles during nitrogen depletion. <i>APE4</i> expression was also induced by the combination of nutrient and thermal stress. Together these results suggest that autophagy is an important cellular process for this microbial pathogen to survive within the environment of the infected host.</p></div