Plasmodium falciparum: stage specific effects of a selective inhibitor of lactate dehydrogenase

Plasmodium falciparum lactate dehydrogenase (PfLDH) is essential for ATP generation. Based on structural differences within the active site between P. falciparum and human LDH, we have identified a series of heterocyclic azole-based inhibitors that selectively bind within the PfLDH but not the human LDH (hLDH) active site and showed anti-malarial activity in vitro and in vivo. Here we expand on an azole, OXD1, from this series and found that the anti-P. falciparum activity was retained against a panel of strains independently of their anti-malarial drug sensitivity profile. Trophozoites had relatively higher PfLDH enzyme activity and PfLDH-RNA expression levels than rings and were the most susceptible stages to OXD1 exposure. This is probably linked to their increased energy requirements and consistent with glycolysis being an essential metabolic pathway for parasite survival within the erythrocyte. Further structural elaboration of these azoles could lead to the identification of compounds that target P. falciparum through such a novel mechanism and with more potent anti-malarial activity.     

Production of ethanol by immobilized Saccharomyces bayanus in an extractive fermentation system

An extractive fermentation system using immobilized yeast cells was developed to study the ethanol production at high sugar concentrations. Organic acids were used as extracting solvents of ethanol and their toxicity was tested in free and k-carrageenan entrapped cell preparations. Immobilization seems to protect cells against solvent toxicity, when long-chain organic acids, e.g., oleic acid, were used, probably due to steric and diffusional limitations, the free cells not being viable at high oleic acid concentrations. The entrapped cells also present a higher metabolic activity than their free counterparts at high glucose concentrations. A solution of 300 g/L of glucose was totally fermented by the immobilized yeast cells, which when free cannot normally convert more than 200 g/L. In situ recovery of ethanol by oleic acid in a batch immobilized cell system led to higher ethanol productivities and to the fermentation of 400 g/L, when an oleic acid/medium ratio of 5 was used.     

Aotus from the southwestern Amazon region is geographically and chromosomally intermediate betweenA. azarae boliviensis andA. infulatus

We described the karyotypes detected in 23Aotus specimens captured on Southwestern Amazon region (63°30'W, 9°00'S). This region should be occupied byA. nigriceps. However, the animals described here have a fur pattern and a karyotypes similar to those ofA. azarae boliviensis andA. infulatus. The females presented 50 chromosomes and the males 49 as a consequence of fusion between the chromosome Y and an autosome. This sample presented polymorphisms of G- and C-banding and NOR-staining. These animals are karyotypically intermediate betweenA. a. boliviensis andA. infulatus. The taxonomy and karyotypic evolution of these taxa are discussed.     

Oviposition, development, and reproduction of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) fed on different hosts of economic importance

The host selection for oviposition by Spodoptera frugiperda (J.E. Smith) among corn, millet, cotton and soybean, and its relationship with the biological characteristics were investigated. Free and non-choice tests for oviposition using plots containing five plants each, from each host in plastic greenhouse, resulted in similar oviposition preference among the host plants. In addition, selected biological characteristics of S. frugiperda were determined in the laboratory with larvae feeding on host leaves, and the combination of leaf and cotton boll. Neonate larvae exhibited low success of colonization on cotton boll compared to the leaves of all other hosts. Spodoptera frugiperda fed only on cotton bolls exhibited longer larval and pupal development, and longer adult life span; however with similar egg production. Larvae fed cotton leaves during six days and then transferred to cotton bolls, however, exhibited development and reproduction similar to those reared on corn or only on cotton leaves. Therefore, the variations on immature stages of S. frugiperda were not related with host selection for oviposition which was similar among the studied hosts. Based on our data, the millet as a winter, rotational, and cover crop is a potential host for S. frugiperda, while leaves and cotton bolls were diets of intermediate suitability as compared to corn and soybean leaves.     

Interaction of Bacillus thuringiensis svar. israelensis Cry toxins with binding sites from Aedes aegypti (Diptera: Culicidae) larvae midgut

This work shows in vitro processing of Bacillus thuringiensis svar. isralensis Cry toxins and the capacity of the active fragments to bind the midgut microvilli of Aedes aegypti larvae. Processing of Cry11Aa, Cry4Aa and Cry4Ba yielded double fragments of 38-30, 45-20 and 45-18 kDa, respectively. Competition assays showed that all active (125)I-Cry toxins are able to specifically bind to brush border membrane fractions and they might share a common class of binding sites. The values of IC(50) suggested that toxins do not display high affinity for the receptors from brush border membrane fractions, while dissociation assays showed that binding was irreversible, indicating the insertion of toxins in the cell membrane.     

Presence of non-suppressive, M2-related dsRNAs molecules in Saccharomyces cerevisiae strains isolated from spontaneous fermentations

Total dsRNA extractions in five killer K2 strains of Saccharomyces cerevisiae isolated from spontaneous fermentations revealed the presence of a novel dsRNA fragment (which we named NS dsRNA) of approximately 1.30 kb, together with L and M2 dsRNAs. NS dsRNA appeared to be encapsidated in the same kind of viral particles as L and M2 dsRNA. Northern blot hybridization experiments indicated that NS dsRNA was derived from M2 dsRNA, likely by deletion of the internal A+U-rich region. However, unlike S dsRNAs (suppressive forms derived from M1 dsRNA in K1 killers), NS dsRNA did not induce exclusion of the parental M2 dsRNA when the host strain was maintained for up to 180 generations of growth.     

Storage proteins in sugarcane: An interesting exception in monocots

Storage proteins were extracted from sugarcane seeds, globular embryos (formed on embryogenic calluses and collected in early developmental stages) and embryogenic cells. In all cases, the major percentage of storage proteins were albumins and globulins and the lower percentage were prolamins and glutelins. Sugarcane is an interesting exception in monocots which usually have high levels of prolamins and glutelins. This revised version was published online in June 2006 with corrections to the Cover Date.