The social amoeba Dictyostelium discoideum has proven to be a useful model for studying relevant aspects of the host-pathogen interaction. In this work, D. discoideum was used as a model to study the ability of Salmonella Typhimurium to survive in amoebae and to evaluate the contribution of selected genes in this process. To do this, we performed infection assays using axenic cultures of D. discoideum co-cultured with wild-type S. Typhimurium and/or defined mutant strains. Our results confirmed that wild-type S. Typhimurium is able to survive intracellularly in D. discoideum. In contrast, mutants AaroA and A waaL are defective in intracellular survival in this amoeba. Next, we included in our study a group of mutants in genes directly linked to Salmonella virulence. Of note, mutants Delta invA, Delta ssaD, Delta cIpV, and Delta phoPQ also showed an impaired ability to survive intracellularly in D, discoideum. This indicates that S. Typhimurium requires a functional biosynthetic pathway of aromatic compounds, a lipopolysaccharide containing a complete O-antigen, the type III secretion systems (T3SS) encoded in SPI-1 and SPI-2, the type VI secretion system (T6SS) encoded in SPI-6 and PhoP/PhoQ two-component system to survive in D. discoideurn. To our knowledge, this is the first report on the requirement of O-antigen and T6SS in the survival of Salmonella within amoebae. In addition, mutants AinvA and AssaD were internalized in higher numbers than the wild -type strain during competitive infections, suggesting that S. Typhimurium requires the T3SS encoded in SPI-1 and SPI-2 to evade phagocytosis by D. discoideum. Altogether, these results indicate that S. Typhimurium exploits a common set of genes and molecular mechanisms to survive within amoeba and animal host cells. The use of D. discoideum as a model for host pathogen interactions will allow us to discover the gene repertoire used by Salmonella to survive inside the amoeba and to study the cellular processes that are affected during infection.FONDECYT 1140754 1120209 1130225 CONICYT 221320275 21120431 21140615 2214075

Microcin E492 (MccE492) is a pore-forming bacteriocin produced and exported by Klebsiella pneumoniae RYC492. Besides its antibacterial activity, excreted MccE492 can form amyloid fibrils in vivo as well as in vitro. It has been proposed that bacterial amyloids can be functional playing a biological role, and in the particular case of MccE492 it would control the antibacterial activity. MccE492 amyloid fibril’s morphology and formation kinetics in vitro have been well-characterized, however, it is not known which amino acid residues determine its amyloidogenic propensity, nor if it forms intracellular amyloid inclusions as has been reported for other bacterial amyloids. In this work we found the conditions in which MccE492 forms intracellular amyloids in Escherichia coli cells, that were visualized as round-shaped inclusion bodies recognized by two amyloidophilic probes, 2-4′-methylaminophenyl benzothiazole and thioflavin-S. We used this property to perform a flow cytometry-based assay to evaluate the aggregation propensity of MccE492 mutants, that were designed using an in silico prediction of putative aggregation hotspots. We established that the predicted amino acid residues 54–63, effectively act as a pro-amyloidogenic stretch. As in the case of other amyloidogenic proteins, this region presented two gatekeeper residues (P57 and P59), which disfavor both intracellular and in vitro MccE492 amyloid formation, preventing an uncontrolled aggregation. Mutants in each of these gatekeeper residues showed faster in vitro aggregation and bactericidal inactivation kinetics, and the two mutants were accumulated as dense amyloid inclusions in more than 80% of E. coli cells expressing these variants. In contrast, the MccE492 mutant lacking residues 54–63 showed a significantly lower intracellular aggregation propensity and slower in vitro polymerization kinetics. Electron microscopy analysis of the amyloids formed in vitro by these mutants revealed that, although with different efficiency, all formed fibrils morphologically similar to wild-type MccE492. The physiological implication of MccE492 intracellular amyloid formation is probably similar to the inactivation process observed for extracellular amyloids, and could be used as a mean of sequestering potentially toxic species inside the cell when this bacteriocin is produced in large amounts.

Translation initiation of the human immunodeficiency virus type-1 (HIV-1) unspliced mRNA has been shown to occur through cap-dependent and IRES-driven mechanisms. Previous studies suggested that the nuclear cap-binding complex (CBC) rather than eIF4E drives cap-dependent translation of the unspliced mRNA and we have recently reported that the CBC subunit CBP80 supports the function of the viral protein Rev during nuclear export and translation of this viral transcript. Ribosome recruitment during CBC-dependent translation of cellular mRNAs relies on the activity CBP80/20 translation initiation factor (CTIF), which bridges CBP80 and the 40S ribosomal subunit through interactions with eIF3g. Here, we report that CTIF restricts HIV-1 replication by interfering with Gag synthesis from the unspliced mRNA. Our results indicate that CTIF associates with Rev through its N-terminal domain and is recruited onto the unspliced mRNA ribonucleoprotein complex in order to block translation. We also demonstrate that CTIF induces the cytoplasmic accumulation of Rev impeding the association of the viral protein with CBP80. We finally show that CTIF restricts HIV-2 but not MLV Gag synthesis indicating an inhibitory mechanism conserved in Rev-expressing human lentiviruses..

Artículo de publicación ISI.In the alpine life-zone, increasingly slower and unpredictable pollination at the higher altitudes predict an increase in floral investment in strongly outcrossing, pollenlimited biotically pollinated plant species, but not in autonomously self-pollinating species. Plant size, floral and above-ground vegetative biomass and individual capitulum biomass were studied in highly autogamous Chaetanthera euphrasioides (DC.) F. Meigen (Asteraceae) at 2,400 m a.s.l. and 3,300–3,400 m a.s.l. in the high Andes of central Chile. Contrary to prediction, altitude had a small positive effect on floral biomass investment and the anisometric relationship between floral investment, and plant size differed at the two altitudes. Individual capitulum size, however, was not affected by altitude. Plastic floral allocation and selection to increase seed production and ameliorate stronger inbreeding at the higher elevations are discussed as possible explanations for the small but unexpected altitudinal increase in floral allocation.Fondecyt-Chil

Actualmente se encuentra en desarrollo una cuarta generación de derechos humanos, entre cuyos contenidos se agrupa lo relativo al despliegue humano a la luz de las tecnologías de la comunicación e información en el ciberespacio. El presente artículo es una reflexión sobre dicho tema, específicamente desde dos perspectivas de lectura. Por una parte, en cuanto a las posibilidades de configuración de tales prerrogativas con base en el concepto de «derechos discursivos», a partir de los planteamientos de Jürgen Habermas, pero revisitados ahora en este nuevo escenario. Por otra, desde la mirada del ciberhumanismo, que permite enriquecer y complementar el prisma habermasiano, habida cuenta de sus limitaciones en el entorno virtual. La pregunta por los Derechos Humanos en el contexto ciberespacial demanda tanto una relectura de los derechos ya existentes, como una dilucidación de nuevas prerrogativas en el marco de la sociedad tecnológica de hoy.