Morphological comparison of axenic amastigogenesis of trypomastigotes and metacyclic forms of Trypanosoma cruzi

Amastigogenesis occurs first when metacyclic trypomastigotes from triatomine urine differentiate into amastigotes inside mammalian host cells and a secondary process when tissue-derived trypomastigotes invade new cells and differentiate newly to amastigotes. Using scanning electron microscopy, we compared the morphological patterns manifested by trypomastigotes and metacyclic forms of Trypanosoma cruzi during their axenic-transformation to amastigotes in acidic medium at 37°C. We show here that in culture MEMTAU medium, secondary and primary axenic amastigogenesis display different morphologies. As already described, we also observed a high differentiation rate of trypomastigotes into amastigotes. Conversely, the transformation rate of in vitro-induced-metacyclic trypomastigotes to amastigotes was significantly slower and displayed distinct patterns of transformation that seem environment-dependent. Morphological comparisons of extracelullar and intracellular amastigotes showed marked similarities, albeit some differences were also detected. SDS-PAGE analyses of protein and glycoprotein from primary and axenic extracelullar amastigotes showed similarities in glycopeptide profiles, but variations between their proteins demonstrated differences in their respective macromolecular constitutions. The data indicate that primary and axenic secondary amastigogenesis of T. cruzi may be the result of different developmental processes and suggest that the respective intracellular mechanisms driving amastigogenesis may not be the same.

Arthropod and filarioid parasites associated with wild rodents in the northeast marshes of Buenos Aires, Argentina

During 1995, 16 species of arthropods and 2 species of filarioids, totaling 1 287 specimens were collected from 64 wild rodents captured in the Hudson Natural Reserve, Buenos Aires, Argentina. Infestation parameters and indexes were analyzed. Host specific richness was S = 6, diversity H = 1.48, and relative density RDI = 40%. High values of parasite species richness and diversity were found on Oligoryzomys delticola (S = 9; H = 1.40), Oxymycterus rufus (S = 9; H = 1.37), and Oligoryzomys flavescens (S = 9; H = 1.28), followed by Scapteromys aquaticus (S = 6; H = 0.17), and Akodon azarae (S = 4; H = 1.20). Deltamys kempi was infested only by Androlaelaps rotundus. O. delticola and O. flavescens showed the highest similarity index (O = 74.19%), followed by O. flavescens with S. aquaticus, as a result of historical processes and shared microhabitats. Considering arthropods-filarioids associations, significant affinity was observed in Litomosoides bonaerensis with Hoplopleura travassosi, Laelaps paulistanensis, and Gigantolaelaps wolffsohni.

Trypanosoma cruzi strains isolated from human, vector, and animal reservoir in the same endemic region in Mexico and typed as T. cruzi I, discrete typing unit 1 exhibit considerable biological diversity

In this study, three strains of Trypanosoma cruzi were isolated at the same time and in the same endemic region in Mexico from a human patient with chronic chagasic cardiomyopathy (RyC-H); vector (Triatoma barberi) (RyC-V); and rodent reservoir (Peromyscus peromyscus) (RyC-R). The three strains were characterized by multilocus enzyme electrophoresis, random amplified polymorphic DNA, and by pathological profiles in experimental animals (biodemes). Based on the analysis of genetic markers the three parasite strains were typed as belonging to T. cruzi I major group, discrete typing unit 1. The pathological profile of RyC-H and RyC-V strains indicated medium virulence and low mortality and, accordingly, the strains should be considered as belonging to biodeme Type III. On the other hand, the parasites from RyC-R strain induced more severe inflammatory processes and high mortality (> 40%) and were considered as belonging to biodeme Type II. The relationship between genotypes and biological characteristics in T. cruzi strains is still debated and not clearly understood. An expert committee recommended in 1999 that Biodeme Type III would correspond to T. cruzi I group, whereas Biodeme Type II, to T. cruzi II group. Our findings suggest that, at least for Mexican isolates, this correlation does not stand and that biological characteristics such as pathogenicity and virulence could be determined by factors different from those identified in the genotypic characterization

Chronofunctions of Heilu soil developed from Loess in Luochuan, on the chinese Loess plateau

Soil chronofunctions are an alternative for the quantification of soil-forming processes and underlie the modeling of soil genesis. To establish soil chronofunctions of a Heilu soil profile on Loess in Luochuan, selected soil properties and the 14C ages in the Holocene were studied. Linear, logarithmic, and third-order polynomial functions were selected to fit the relationships between soil properties and ages. The results indicated that third-order polynomial function fit best for the relationships between clay (< 0.002 mm), silt (0.002-0.02 mm), sand (0.02-2 mm) and soil ages, and a trend of an Ah horizon ocurrence in the profile. The logarithmic function indicated mainly variations of soil organic carbon and pH with time (soil age). The variation in CaCO3 content, Mn/Zr, Fe/Zr, K/Zr, Mg/Zr, Ca/Zr, P/Zr, and Na/Zr ratios with soil age were best described by three-order polynomial functions, in which the trend line showed migration of CaCO3 and some elements.

Chemical dispersants and pre-treatments to determine clay in soils with different mineralogy

Knowledge of the soil physical properties, including the clay content, is of utmost importance for agriculture. The behavior of apparently similar soils can differ in intrinsic characteristics determined by different formation processes and nature of the parent material. The purpose of this study was to assess the efficacy of separate or combined pre-treatments, dispersion methods and chemical dispersant agents to determine clay in some soil classes, selected according to their mineralogy. Two Brazilian Oxisols, two Alfisols and one Mollisol with contrasting mineralogy were selected. Different treatments were applied: chemical substances as dispersants (lithium hydroxide, sodium hydroxide, and hexametaphosphate); pre-treatment with dithionite, ammonium oxalate, and hydrogen peroxide to eliminate organic matter; and coarse sand as abrasive and ultrasound, to test their mechanical action. The conclusion was drawn that different treatments must be applied to determine clay, in view of the soil mineralogy. Lithium hydroxide was not efficient to disperse low-CEC electropositive soils and very efficient in dispersing high-CEC electronegative soils. The use of coarse sand as an abrasive increased the clay content of all soils and in all treatments in which dispersion occurred, with or without the use of chemical dispersants. The efficiency of coarse sand is not the same for all soil classes.

Soil infiltration based on bp neural network and grey relational analysis

Soil infiltration is a key link of the natural water cycle process. Studies on soil permeability are conducive for water resources assessment and estimation, runoff regulation and management, soil erosion modeling, nonpoint and point source pollution of farmland, among other aspects. The unequal influence of rainfall duration, rainfall intensity, antecedent soil moisture, vegetation cover, vegetation type, and slope gradient on soil cumulative infiltration was studied under simulated rainfall and different underlying surfaces. We established a six factor-model of soil cumulative infiltration by the improved back propagation (BP)-based artificial neural network algorithm with a momentum term and self-adjusting learning rate. Compared to the multiple nonlinear regression method, the stability and accuracy of the improved BP algorithm was better. Based on the improved BP model, the sensitive index of these six factors on soil cumulative infiltration was investigated. Secondly, the grey relational analysis method was used to individually study grey correlations among these six factors and soil cumulative infiltration. The results of the two methods were very similar. Rainfall duration was the most influential factor, followed by vegetation cover, vegetation type, rainfall intensity and antecedent soil moisture. The effect of slope gradient on soil cumulative infiltration was not significant.

Knowledge management: uncovering risky gaps underlying the criticisms and moving to another perspective

The comments related to the sustainability of knowledge management (KM) have shown signs that it possibly can be a discourse which determines a quick style, but otherwise have also allowed the building of a better understanding about the limits and weaknesses of the knowlege management. In addition to the criticisms, the conceptual bases of knowledge management have been undermined by a contradictory combination of paradigms; there are also contradictions between the theoretical perspective jubjacent to the knwoledge management and its operationality. As a way of minimizing the possibility that the knowledge management may be turned into an umbrella concept and fail, it is suggested that its approaches embody a more interpretative perspective, taking up the role of an instrument which enables and facilitates the processes and practices in building up knowledge and information, enhancing their focus on the support to the establishment of human competences in order to deal intelligently with the present overcharge of information resources and need for building up information in the organizations.

Sustainability, certification, and regulation of biochar

Biochar has a relatively long half-life in soil and can fundamentally alter soil properties, processes, and ecosystem services. The prospect of global-scale biochar application to soils highlights the importance of a sophisticated and rigorous certification procedure. The objective of this work was to discuss the concept of integrating biochar properties with environmental and socioeconomic factors, in a sustainable biochar certification procedure that optimizes complementarity and compatibility between these factors over relevant time periods. Biochar effects and behavior should also be modelled at temporal scales similar to its expected functional lifetime in soils. Finally, when existing soil data are insufficient, soil sampling and analysis procedures need to be described as part of a biochar certification procedure.