Adhesion of Histoplasma capsulatum to pneumocytes and biofilm formation on an abiotic surface

The pathogenic fungus, Histoplasma capsulatum, causes the respiratory and systemic disease 'histoplasmosis'. This disease is primarily acquired via inhalation of aerosolized microconidia or hyphal fragments of H. capsulatum. Evolution of this respiratory disease depends on the ability of H. capsulatum yeasts to survive and replicate within alveolar macrophages. It is known that adhesion to host cells is the first step in colonization and biofilm formation. Some microorganisms become attached to biological and non-biological surfaces due to the formation of biofilms. Based on the importance of biofilms and their persistence on host tissues and cell surfaces, the present study was designed to investigate biofilm formation by H. capsulatum yeasts, as well as their ability to adhere to pneumocyte cells. H. capsulatum biofilm assays were performed in vitro using two different clinical strains of the fungus and biofilms were characterized using scanning electron microscopy. The biofilms were measured using a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium-hydroxide (XTT) reduction assay. The results showed that both the H. capsulatum strains tested were very efficient at adhering to host cells and forming biofilm. Therefore, this is a possible survival strategy adopted by this fungus.     

Adenosine Deaminase Activity in Serum and Lymphocytes of Rats Infected with Sporothrix schenckii

Sporotrichosis is a fungal infection of subcutaneous or chronic evolution, inflammatory lesions characterized by their pyogranulomatous aspect, caused by the dimorphic fungus Sporothrix schenckii. Adenosine deaminase (ADA) is a "key" enzyme in the purine metabolism, promoting the deamination of adenosine, an important anti-inflammatory molecule. The increase in ADA activity has been demonstrated in several inflammatory conditions; however, there are no data in the literature associated with this fungal infection. The objective of this study was to evaluate the activity of serum ADA (S-ADA) and lymphocytes (L-ADA) of rats infected with S. schenckii. We used seventy-eight rats divided into two groups. In the first experiment, rats were infected subcutaneously and in the second experiment, infected intraperitoneally. Blood samples for hematologic evaluation and activities of S-ADA and L-ADA were performed at days 15, 30, and 40 post-infection (PI) to assess disease progression. In the second experiment, it was observed an acute decrease in activity of S-ADA and L-ADA (P?相似文献   

Epicormic ontogeny in Quercus petraea constrains the highly plausible control of epicormic sprouting by water and carbohydrates

Background and Aims

There is increasing evidence that suppressed bud burst and thus epicormic shoot emergence (sprouting) are controlled by water–carbohydrate supplies to entire trees and buds. This direct evidence is still lacking for oak. In other respects, recent studies focused on sessile oak, Quercus petraea, have confirmed the important constraints of sprouting by epicormic ontogeny. The main objective of this paper was thus to provide provisional confirmation of the water–carbohydrate control and direct evidence of the ontogenic constraints by bringing together results already published in separate studies on water status and distribution of carbohydrates, and on accompanying vegetation and epicormics, which also quantify epicormic ontogeny.

Methods

This paper analyses results gained from a sessile oak experiment in which part of the site was free from fairly tall, dense accompanying vegetation. This experiment was initially focused on stand water status and more recently on the carbohydrate distribution of dominant trees. External observations of the epicormic composition and internal observations with X-ray computer tomography were undertaken on 60 and six trees, respectively.

Key Results

Sprouting was more intense in the part of the stand free from accompanying vegetation and on upper trunk segments. A clear effect of epicormic ontogeny was demonstrated as well: the more epicormics a trunk segment bears, the more chances it had to bear sprouts.

Conclusions

These results indirectly infer water–carbohydrate control and show direct evidence of constraints by epicormic ontogeny. These results have far-reaching consequences related to the quantification of all functions fulfilled by any type of epicormic structure in any part of the tree.     

Floristics and environmental factors determining the geographic distribution of epiphytic bromeliads in the Brazilian Atlantic Rain Forest

We investigated how epiphytic species and subfamilies of Bromeliaceae change along the extent of the Atlantic Rain Forest, to answer the questions: (i) How do the epiphytic genera and subfamilies of Bromeliaceae change along the domain? (ii) How similar are the different regions of the Atlantic Rain Forest in relation to the epiphytic species of bromeliads? (iii) Which environmental variables are the most important factors in determining species composition along the domain? We found 114 species of Bromelioideae and 73 of Tillandsioideae. The predominance of Bromelioideae was unexpected, because they are not wind-dispersed as would be expected for most epiphytes. The smaller number of species of Tillandsioideae, and the high frequency of species of Vriesea with limited geographic distributions indicated that epiphytes with rather limited geographic distributions predominate in this domain. Species similarity was divided into one block of south–southeastern localities, and a second block of northeastern–southeastern localities. These results suggest that the distribution of epiphytic bromeliad species resembles that of the phorophyte trees, more than a previous pattern suggested for all epiphytes in the domain. Latitude, temperature and altitude were important factors affecting the species composition along the domain. In general, our results differ from those of other studies in Latin America, and we suggest that historical and evolutionary events generated these differences.     

Heterogeneity of the digestible insoluble fiber of selected forages in situ

Long-term in situ incubations were performed to verify the likelihood of the heterogeneity concept of the potentially digestible fraction of the insoluble fiber (NDFom) by fitting both heterogeneous and homogeneous potentially digestible NDFom versions of a generalized compartmental model of digestion (GCMD). Corn silage and eleven tropical grasses and alfalfa hay were studied. Data were gathered from a study in which forage samples in nylon bags were incubated in rumen cannulated steers so that three profiles per forage were generated. The incubation endpoint was used to form sets of time profiles. The original set consisted of profiles ending at 1440 h, and the other two were formed by using 96 and 240 h as the incubation endpoints, respectively. The indigestible residue was estimated using nonlinear least squares or by assuming it to be 2.4 times lignin determined by the sulphuric acid method (Lignin (sa)). Therefore, eight different models were evaluated by combining end points of digestion, and the homogeneous and heterogeneous versions of GCMD with the two ways of estimating the indigestible residue. The likelihood of the models was assessed by computing Akaike information criteria. The effects of forage, model, and their interaction were analyzed by taking model as a repeated measurement. Heterogeneity of the potentially degradable fraction for NDFom was detected with long-term incubation trials (up to 1440 h) for some forages, and the introduction of the 2.4×Lignin (sa) as a direct measure of the indigestible residue improved the likelihood of the heterogeneous version of GCMD. The forage by model interaction was significant for many comparable parameter estimates, which means that specific and inconsistent results for models within forages were produced depending on the definition of the incubation end-point. The indigestible residue was overestimated with short-term incubation profiles, but the overestimation was lower for the profiles ending at 240 h whether compared to profiles ending at 96 h. Given the likelihood of the heterogeneous version of GCMD fitted to profiles ending at 1440 h and at 240 h for some forages, the heterogeneity concept should be investigated whenever the research interest relies on estimating the kinetic attributes of the degradation profiles of the NDFom in situ.     

Chromatin-mediated Candida albicans virulence

Candida albicans is the most prevalent human fungal pathogen. To successfully propagate an infection, this organism relies on the ability to change morphology, express virulence-associated genes and resist DNA damage caused by the host immune system. Many of these events involve chromatin alterations that are crucial for virulence. This review will focus on the studies that have been conducted on how chromatin function affects pathogenicity of C. albicans and other fungi. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.     

Chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence study revealing effects of flooding in canola hybrids

By generating stress conditions soil flooding can induce alterations in the cell metabolism and thus is detrimental to plant growth. This study was done under the greenhouse conditions to determine the effect of soil flooding on the chlorophyll fluorescence of some hybrids of canola (Brassica napus L.). Fifty five days old plants were subjected to flooding for six days. There was no difference in the parameters modulate chlorophyll fluorescence, in contrast, some the parameters related to the energy flux in photosystem II varied due to flooding stress. At the end of the six days, the performance indexes (PI_total and PI_ABS) decreased, in all hybrids except in ‘Hyola 420’. The difference kinetics of the chlorophyll a fluorescence transient showed different effects on different sites of the photosynthetic machinery. It could be concluded that compared to the other hybrids, ‘Hyola 420’ was less sensitive to flooding.     

Selective inhibition of biotin protein ligase from Staphylococcus aureus

There is a well documented need to replenish the antibiotic pipeline with new agents to combat the rise of drug resistant bacteria. One strategy to combat resistance is to discover new chemical classes immune to current resistance mechanisms that inhibit essential metabolic enzymes. Many of the obvious drug targets that have no homologous isozyme in the human host have now been investigated. Bacterial drug targets that have a closely related human homologue represent a new frontier in antibiotic discovery. However, to avoid potential toxicity to the host, these inhibitors must have very high selectivity for the bacterial enzyme over the human homolog. We have demonstrated that the essential enzyme biotin protein ligase (BPL) from the clinically important pathogen Staphylococcus aureus could be selectively inhibited. Linking biotin to adenosine via a 1,2,3 triazole yielded the first BPL inhibitor selective for S. aureus BPL over the human equivalent. The synthesis of new biotin 1,2,3-triazole analogues using click chemistry yielded our most potent structure (K(i) 90 nM) with a >1100-fold selectivity for the S. aureus BPL over the human homologue. X-ray crystallography confirmed the mechanism of inhibitor binding. Importantly, the inhibitor showed cytotoxicity against S. aureus but not cultured mammalian cells. The biotin 1,2,3-triazole provides a novel pharmacophore for future medicinal chemistry programs to develop this new antibiotic class.     

Role of the Actin Ala-108–Pro-112 Loop in Actin Polymerization and ATPase Activities

Actin plays fundamental roles in a variety of cell functions in eukaryotic cells. The polymerization-depolymerization cycle, between monomeric G-actin and fibrous F-actin, drives essential cell processes. Recently, we proposed the atomic model for the F-actin structure and found that actin was in the twisted form in the monomer and in the untwisted form in the filament. To understand how the polymerization process is regulated (Caspar, D. L. (1991) Curr. Biol. 1, 30–32), we need to know further details about the transition from the twisted to the untwisted form. For this purpose, we focused our attention on the Ala-108–Pro-112 loop, which must play crucial roles in the transition, and analyzed the consequences of the amino acid replacements on the polymerization process. As compared with the wild type, the polymerization of P109A was accelerated in both the nucleation and the elongation steps, and this was attributed to an increase in the frequency factor of the Arrhenius equation. The multiple conformations allowed by the substitution presumably resulted in the effective formation of the collision complex, thus accelerating polymerization. On the other hand, the A108G mutation reduced the rates of both nucleation and elongation due to an increase in the activation energy. In the cases of polymerization acceleration and deceleration, each functional aberration is attributed to a distinct elementary process. The rigidity of the loop, which mediates neither too strong nor too weak interactions between subdomains 1 and 3, might play crucial roles in actin polymerization.