Xylem cavitation vulnerability influences tree species’ habitat preferences in miombo woodlands

Although precipitation plays a central role in structuring Africa’s miombo woodlands, remarkably little is known about plant-water relations in this seasonally dry tropical forest. Therefore, in this study, we investigated xylem vulnerability to cavitation for nine principal tree species of miombo woodlands, which differ in habitat preference and leaf phenology. We measured cavitation vulnerability (Ψ₅₀), stem-area specific hydraulic conductivity (K _S), leaf specific conductivity (K _L), seasonal variation in predawn water potential (Ψ_PD) and xylem anatomical properties [mean vessel diameter, mean hydraulic diameter, mean hydraulic diameter accounting for 95 % flow, and maximum vessel length (V _L)]. Results show that tree species with a narrow habitat range (mesic specialists) were more vulnerable to cavitation than species with a wide habitat range (generalists). Ψ₅₀ for mesic specialists ranged between ?1.5 and ?2.2 MPa and that for generalists between ?2.5 and ?3.6 MPa. While mesic specialists exhibited the lowest seasonal variation in Ψ_PD, generalists displayed significant seasonal variations in Ψ_PD suggesting that the two miombo habitat groups differ in their rooting depth. We observed a strong trade-off between K _S and Ψ₅₀ suggesting that tree hydraulic architecture is one of the decisive factors setting ecological boundaries for principal miombo species. While vessel diameters correlated weakly (P > 0.05) with Ψ₅₀, V _L was positively and significantly correlated with Ψ₅₀. Ψ_PD was significantly correlated with Ψ₅₀ further reinforcing the conclusion that tree hydraulic architecture plays a significant role in species’ habitat preference in miombo woodlands.     

Selective antibacterial activity of the cationic peptide PaDBS1R6 against Gram-negative bacteria

Infections caused by Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa foremost among them, constitute a major worldwide health problem. Bioinformatics methodologies are being used to rationally design new antimicrobial peptides, a potential alternative for treating these infections. One of the algorithms used to develop antimicrobial peptides is the Joker, which was used to design the peptide PaDBS1R6. This study evaluates the antibacterial activities of PaDBS1R6 in vitro and in vivo, characterizes the peptide interaction to target membranes, and investigates the PaDBS1R6 structure in contact with mimetic vesicles. Moreover, we demonstrate that PaDBS1R6 exhibits selective antimicrobial activity against Gram-negative bacteria. In the presence of negatively charged and zwitterionic lipids the structural arrangement of PaDBS1R6 transits from random coil to α-helix, as characterized by circular dichroism. The tertiary structure of PaDBS1R6 was determined by NMR in zwitterionic dodecylphosphocholine (DPC) micelles. In conclusion, PaDBS1R6 is a candidate for the treatment of nosocomial infections caused by Gram-negative bacteria, as template for producing other antimicrobial agents.     

The sample processing time interval as an influential factor in flow cytometry analysis of lymphocyte subsets

The objective of this paper is to propose a protocol to analyze blood samples in yellow fever 17DD vaccinated which developed serious adverse events. We investigated whether or not the time between sample collection and sample processing could interfere in lymphocyte subset percentage, for it is often impossible to analyze blood samples immediately after collection due to transport delay from collection places to the flow cytometry facility. CD4+CD38+ T, CD8+CD38+ T, CD3+ T, CD19+ B lymphocyte subsets were analyzed by flow cytometry in nine healthy volunteers immediately after blood collection and after intervals of 24 and 48 h. The whole blood lysis method and gradient sedimentation by Histopaque were applied to isolate peripheral blood mononuclear cells for flow cytometry analyses. With the lysis method, there was no significant change in lymphocyte subset percentage between the two time intervals (24 and 48 h). In contrast, when blood samples were processed by Histopaque gradient sedimentation, time intervals for sample processing influenced the percentage in T lymphocyte subsets but not in B cells. From the results obtained, we could conclude that the whole blood lysis method is more appropriate than gradient sedimentation by Histopaque for immunophenotyping of blood samples collected after serious adverse events, due to less variation in the lymphocyte subset levels with respect to the time factor.     

Trypanosoma cruzi: desferrioxamine decreases mortality and parasitemia in infected mice through a trypanostatic effect

Desferrioxamine (DFO) is a potent iron chelator that is also known to modulate inflammation and act as an efficient antioxidant under normal conditions and under oxidative stress. Many in vitro and in vivo studies have shown the efficacy of DFO in the treatment of viral, bacterial and protozoan infections. DFO is known to reduce the intensity of Trypanosoma cruzi infections in mice even during a course of therapy that is not effective in maintaining anaemia or low iron levels. To further clarify these findings, we investigated the action of DFO on mouse T. cruzi infection outcomes and the direct impact of DFO on parasites.Infected animals treated with DFO (5 mg/animal/day) for 35 days, beginning 14 days prior to infection, presented lower parasitemia and lower cumulative mortality rate. No significant effect was observed on iron metabolism markers, erythrograms, leukograms or lymphocyte subsets.In the rapid method for testing in vivo T. cruzi susceptibility, DFO also induced lower parasitemia.In regard to its direct impact on parasites, DFO slightly inhibited the growth of amastigotes and trypomastigotes in fibroblast culture. Trypan blue staining showed no effects of DFO on parasite viability, and only minor apoptosis in trypomastigotes was observed. Nevertheless, a clear decrease in parasite mobility was detected.In conclusion, the beneficial actions of DFO on mice T. cruzi infection seem to be independent of host iron metabolism and free of significant haematological side effects. Through direct action on the parasite, DFO has more effective trypanostatic than trypanocidal properties.     

Comparison of Penicillium echinulatum and Trichoderma reesei cellulases in relation to their activity against various cellulosic substrates

Penicillium echinulatum has been identified as a potential cellulase producer for bioconversion processes but its cellulase system has never been investigated in detail. In this work, the volumetric activities of P. echinulatum cellulases were determined against filter paper (0.27 U/mL), carboxymethylcellulose (1.53 U/mL), hydroxyethylcellulose (4.68 U/mL), birchwood xylan (3.16 U/mL), oat spelt xylan (3.29 U/mL), Sigmacell type 50 (0.10 U/mL), cellobiose (0.19 U/mL), and p-nitrophenyl-glucopiranoside (0.31 U/mL). These values were then expressed in relation to the amount of protein and compared those of Trichoderma reesei cellulases (Celluclast 1.5L FG, Novozymes). Both enzyme complexes were shown to have similar total cellulase and xylanase activities. Analysis of substrate hydrolysates demonstrated that P. echinulatum enzymes have higher beta-glucosidase activity than Celluclast 1.5L FG, while the latter appears to have greater cellobiohydrolase activity. Unlike Celluclast 1.5L FG, P. echinulatum cellulases had enough beta-glucosidase activity to remove most of the cellobiose produced in hydrolysis experiments. However, Celluclast 1.5L FG became more powerful than P. echinulatum cellulases when supplemented with exogenous beta-glucosidase activity (Novozym 188). Both cellulase complexes displayed the same influence over the degree of polymerization of cellulose, revealing that hydrolyzes were carried out under the typical endo-exo synergism of fungal enzymes.     

Function inferences from a molecular structural model of bacterial ParE toxin

Toxin-antitoxin (TA) systems contribute to plasmid stability by a mechanism that relies on the differential stabilities of the toxin and antitoxin proteins and leads to the killing of daughter bacteria that did not receive a plasmid copy at the cell division. ParE is the toxic component of a TA system that constitutes along with RelE an important class of bacterial toxin called RelE/ParE superfamily. For ParE toxin, no crystallographic structure is available so far and rare in vitro studies demonstrated that the target of toxin activity is E. coli DNA gyrase. Here, a 3D Model for E. coli ParE toxin by molecular homology modeling was built using MODELLER, a program for comparative modeling. The Model was energy minimized by CHARMM and validated using PROCHECK and VERIFY3D programs. Resulting Ramachandran plot analysis it was found that the portion residues failing into the most favored and allowed regions was 96.8%. Structural similarity search employing DALI server showed as the best matches RelE and YoeB families. The Model also showed similarities with other microbial ribonucleases but in a small score. A possible homologous deep cleft active site was identified in the Model using CASTp program. Additional studies to investigate the nuclease activity in members of ParE family as well as to confirm the inhibitory replication activity are needed. The predicted Model allows initial inferences about the unexplored 3D structure of the ParE toxin and may be further used in rational design of molecules for structure-function studies.     

Tet1 and Tet2 regulate 5-hydroxymethylcytosine production and cell lineage specification in mouse embryonic stem cells

TET family enzymes convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. Here, we show that Tet1 and Tet2 are Oct4-regulated enzymes that together sustain 5hmC in mouse embryonic stem cells (ESCs) and are induced concomitantly with 5hmC during reprogramming of fibroblasts to induced pluripotent stem cells. ESCs depleted of Tet1 by RNAi show diminished expression of the Nodal antagonist Lefty1 and display hyperactive Nodal signaling and skewed differentiation into the endoderm-mesoderm lineage in embryoid bodies in?vitro. In Fgf4- and heparin-supplemented culture conditions, Tet1-depleted ESCs activate the trophoblast stem cell lineage determinant Elf5 and can colonize the placenta in midgestation embryo chimeras. Consistent with these findings, Tet1-depleted ESCs?form aggressive hemorrhagic teratomas with increased endoderm, reduced neuroectoderm, and ectopic appearance of trophoblastic giant cells. Thus, 5hmC is an epigenetic modification associated with the pluripotent state, and Tet1 functions to regulate the lineage differentiation potential of ESCs.     

The Expression of Connexins and SOX2 Reflects the Plasticity of Glioma Stem-Like Cells

Glioblastoma (GBM) is the most malignant primary brain tumor, with an average survival rate of 15 months. GBM is highly refractory to therapy, and such unresponsiveness is due, primarily, but not exclusively, to the glioma stem-like cells (GSCs). This subpopulation express stem-like cell markers and is responsible for the heterogeneity of GBM, generating multiple differentiated cell phenotypes. However, how GBMs maintain the balance between stem and non-stem populations is still poorly understood. We investigated the GBM ability to interconvert between stem and non-stem states through the evaluation of the expression of specific stem cell markers as well as cell communication proteins. We evaluated the molecular and phenotypic characteristics of GSCs derived from differentiated GBM cell lines by comparing their stem-like cell properties and expression of connexins. We showed that non-GSCs as well as GSCs can undergo successive cycles of gain and loss of stem properties, demonstrating a bidirectional cellular plasticity model that is accompanied by changes on connexins expression. Our findings indicate that the interconversion between non-GSCs and GSCs can be modulated by extracellular factors culminating on differential expression of stem-like cell markers and cell-cell communication proteins. Ultimately, we observed that stem markers are mostly expressed on GBMs rather than on low-grade astrocytomas, suggesting that the presence of GSCs is a feature of high-grade gliomas. Together, our data demonstrate the utmost importance of the understanding of stem cell plasticity properties in a way to a step closer to new strategic approaches to potentially eliminate GSCs and, hopefully, prevent tumor recurrence.     

Impact of Epstein-Barr virus co-infection on natural acquired Plasmodium vivax antibody response

BackgroundThe simultaneous infection of Plasmodium falciparum and Epstein-Barr virus (EBV) could promote the development of the aggressive endemic Burkitt’s Lymphoma (eBL) in children living in P. falciparum holoendemic areas. While it is well-established that eBL is not related to other human malaria parasites, the impact of EBV infection on the generation of human malaria immunity remains largely unexplored. Considering that this highly prevalent herpesvirus establishes a lifelong persistent infection on B-cells with possible influence on malaria immunity, we hypothesized that EBV co-infection could have impact on the naturally acquired antibody responses to P. vivax, the most widespread human malaria parasite.Methodology/Principal findingsThe study design involved three cross-sectional surveys at six-month intervals (baseline, 6 and 12 months) among long-term P. vivax exposed individuals living in the Amazon rainforest. The approach focused on a group of malaria-exposed individuals whose EBV-DNA (amplification of balf-5 gene) was persistently detected in the peripheral blood (PersV_DNA, n = 27), and an age-matched malaria-exposed group whose EBV-DNA could never be detected during the follow-up (NegV_DNA, n = 29). During the follow-up period, the serological detection of EBV antibodies to lytic/ latent viral antigens showed that IgG antibodies to viral capsid antigen (VCA-p18) were significantly different between groups (PersV_DNA > NegV_DNA). A panel of blood-stage P. vivax antigens covering a wide range of immunogenicity confirmed that in general PersV_DNA group showed low levels of antibodies as compared with NegV_DNA. Interestingly, more significant differences were observed to a novel DBPII immunogen, named DEKnull-2, which has been associated with long-term neutralizing antibody response. Differences between groups were less pronounced with blood-stage antigens (such as MSP1-19) whose levels can fluctuate according to malaria transmission.Conclusions/SignificanceIn a proof-of-concept study we provide evidence that a persistent detection of EBV-DNA in peripheral blood of adults in a P. vivax semi-immune population may impact the long-term immune response to major malaria vaccine candidates.     

Leishmania braziliensis causing human disease in Northeast Brazil presents loci with genotypes in long-term equilibrium

BackgroundLeishmaniases are neglected tropical diseases that inflict great burden to poor areas of the globe. Intense research has aimed to identify parasite genetic signatures predictive of infection outcomes. Consistency of diagnostic tools based on these markers would greatly benefit from accurate understanding of Leishmania spp. population genetics. We explored two chromosomal loci to characterize a population of L. braziliensis causing human disease in Northeast Brazil.Methodology/Principal findingsTwo temporally distinct samples of L. braziliensis were obtained from patients attending the leishmaniasis clinic at the village of Corte de Pedra: (2008–2011) primary sample, N = 120; (1999–2001) validation sample, N = 35. Parasites were genotyped by Sanger’s sequencing of two 600 base pairs loci starting at nucleotide positions 3,074 and 425,451 of chromosomes 24 and 28, respectively. Genotypes based on haplotypes of biallelic positions in each locus were tested for several population genetic parameters as well as for geographic clustering within the region. Ample geographic overlap of genotypes at the two loci was observed as indicated by non-significant Cusick and Edward’s comparisons. No linkage disequilibrium was detected among combinations of haplotypes for both parasite samples. Homozygous and heterozygous genotypes displayed Hardy-Weinberg equilibrium (HWE) at both loci in the two samples when straight observed and expected counts were compared by Chi-square (p>0.5). However, Bayesian statistics using one million Monte-Carlo randomizations disclosed a less robust HWE for chromosome 24 genotypes, particularly in the primary sample (p = 0.04). Fixation indices (Fst) were consistently lower than 0.05 among individuals of the two samples at both tested loci, and no intra-populational structuralization could be detected using STRUCTURE software.Conclusions/SignificanceThese findings suggest that L. braziliensis can maintain stable populations in foci of human leishmaniasis and are capable of robust genetic recombination possibly due to events of sexual reproduction during the parasite’s lifecycle.