Bidentate Substrate Binding Mode in Oxalate Decarboxylase.

Oxalate decarboxylase is an Mn- and O2-dependent enzyme in the bicupin superfamily that catalyzes the redox-neutral disproportionation of the oxalate monoanion to form carbon dioxide and formate. Its best-studied isozyme is from Bacillus subtilis where it is stress-induced under low pH conditions. Current mechanistic schemes assume a monodentate binding mode of the substrate to the N-terminal active site Mn ion to make space for a presumed O2 molecule, despite the fact that oxalate generally prefers to bind bidentate to Mn. We report on X-band 13C-electron nuclear double resonance (ENDOR) experiments on 13C-labeled oxalate bound to the active-site Mn(II) in wild-type oxalate decarboxylase at high pH, the catalytically impaired W96F mutant enzyme at low pH, and Mn(II) in aqueous solution. The ENDOR spectra of these samples are practically identical, which shows that the substrate binds bidentate (κO, κO') to the active site Mn(II) ion. Domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD) calculations of the expected 13C hyperfine coupling constants for bidentate bound oxalate predict ENDOR spectra in good agreement with the experiment, supporting bidentate bound substrate. Geometry optimization of a substrate-bound minimal active site model by density functional theory shows two possible substrate coordination geometries, bidentate and monodentate. The bidentate structure is energetically preferred by ~4.7 kcal/mol. Our results revise a long-standing hypothesis regarding substrate binding in the enzyme and suggest that dioxygen does not bind to the active site Mn ion after substrate binds. The results are in agreement with our recent mechanistic hypothesis of substrate activation via a long-range electron transfer process involving the C-terminal Mn ion.

Coaxially Conductive Organic Wires Through Self-Assembly.

Here, we describe the synthesis of the hexameric macrocyclic aniline (MA[6]), which spontaneously assembles into coaxially conductive organic wires in its oxidized and acidified emeraldine salt (ES) form. Electrical measurements reveal that ES-MA[6] exhibits high electrical conductivity (7.5 × 10-2 S·cm-1) and that this conductivity is acid-base responsive. Single-crystal X-ray crystallography reveals that ES-MA[6] assembles into well-defined trimeric units that then stack into nanotubes with regular channels, providing a potential route to synthetic nanotubes that are leveraged for ion or small molecule transport. Ultraviolet-visible-near-infrared absorbance spectroscopy and electron paramagnetic spectroscopy showcase the interconversion between acidic (conductive) and basic (insulating) forms of these macrocycles and how charge carriers are formed through protonation, giving rise to the experimentally observed high electrical conductivity.

Oxalate decarboxylase uses electron hole hopping for catalysis.

The hexameric low-pH stress response enzyme oxalate decarboxylase catalyzes the decarboxylation of the oxalate mono-anion in the soil bacterium Bacillus subtilis. A single protein subunit contains two Mn-binding cupin domains, and catalysis depends on Mn(III) at the N-terminal site. The present study suggests a mechanistic function for the C-terminal Mn as an electron hole donor for the N-terminal Mn. The resulting spatial separation of the radical intermediates directs the chemistry toward decarboxylation of the substrate. A π-stacked tryptophan pair (W96/W274) links two neighboring protein subunits together, thus reducing the Mn-to-Mn distance from 25.9 Å (intrasubunit) to 21.5 Å (intersubunit). Here, we used theoretical analysis of electron hole-hopping paths through redox-active sites in the enzyme combined with site-directed mutagenesis and X-ray crystallography to demonstrate that this tryptophan pair supports effective electron hole hopping between the C-terminal Mn of one subunit and the N-terminal Mn of the other subunit through two short hops of ∼8.5 Å. Replacement of W96, W274, or both with phenylalanine led to a large reduction in catalytic efficiency, whereas replacement with tyrosine led to recovery of most of this activity. W96F and W96Y mutants share the wildtype tertiary structure. Two additional hole-hopping networks were identified leading from the Mn ions to the protein surface, potentially protecting the enzyme from high Mn oxidation states during turnover. Our findings strongly suggest that multistep hole-hopping transport between the two Mn ions is required for enzymatic function, adding to the growing examples of proteins that employ aromatic residues as hopping stations.

Epoxyqueuosine Reductase QueH in the Biosynthetic Pathway to tRNA Queuosine Is a Unique Metalloenzyme.

Queuosine is a structurally unique and functionally important tRNA modification, widely distributed in eukaryotes and bacteria. The final step of queuosine biosynthesis is the reduction/deoxygenation of epoxyqueuosine to form the cyclopentene motif of the nucleobase. The chemistry is performed by the structurally and functionally characterized cobalamin-dependent QueG. However, the queG gene is absent from several bacteria that otherwise retain queuosine biosynthesis machinery. Members of the IPR003828 family (previously known as DUF208) have been recently identified as nonorthologous replacements of QueG, and this family was renamed QueH. Here, we present the structural characterization of QueH from Thermotoga maritima. The structure reveals an unusual active site architecture with a [4Fe-4S] metallocluster along with an adjacent coordinated iron metal. The juxtaposition of the cofactor and coordinated metal ion predicts a unique mechanism for a two-electron reduction/deoxygenation of epoxyqueuosine. To support the structural characterization, in vitro biochemical and genomic analyses are presented. Overall, this work reveals new diversity in the chemistry of iron/sulfur-dependent enzymes and novel insight into the last step of this widely conserved tRNA modification.

[Distribution patterns of canopy and understory tree species at local scale in a Tierra Firme forest, the Colombian Amazonia]. / Patrones de distribución de especies arbóreas de dosel y sotobosque a escala local en bosques de tierra firme, Amazonia colombiana.

The effect of environmental variation on the structure of tree communities in tropical forests is still under debate. There is evidence that in landscapes like Tierra Firme forest, where the environmental gradient decreases at a local level, the effect of soil on the distribution patterns of plant species is minimal, happens to be random or is due to biological processes. In contrast, in studies with different kinds of plants from tropical forests, a greater effect on floristic composition of varying soil and topography has been reported. To assess this, the current study was carried out in a permanent plot of ten hectares in the Amacayacu National Park, Colombian Amazonia. To run the analysis, floristic and environmental variations were obtained according to tree species abundance categories and growth forms. In order to quantify the role played by both environmental filtering and dispersal limitation, the variation of the spatial configuration was included. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the species distribution patterns. The spatial template was evaluated using the Principal Coordinates of Neighbor Matrix method. We recorded 14 074 individuals from 1 053 species and 80 families. The most abundant families were Myristicaceae, Moraceae, Meliaceae, Arecaceae and Lecythidaceae, coinciding with other studies from Northwest Amazonia. Beta diversity was relatively low within the plot. Soils were very poor, had high aluminum concentration and were predominantly clayey. The floristic differences explained along the ten hectares plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on Tierra Firme forests of Amacayacu National Park, and suggest reserve's size as a key element to ensure the conservation of plant diversity at both regional and local levels.

Selective incorporation of 5-hydroxytryptophan blocks long range electron transfer in oxalate decarboxylase.

Oxalate decarboxylase from Bacillus subtilis is a binuclear Mn-dependent acid stress response enzyme that converts the mono-anion of oxalic acid into formate and carbon dioxide in a redox neutral unimolecular disproportionation reaction. A π-stacked tryptophan dimer, W96 and W274, at the interface between two monomer subunits facilitates long-range electron transfer between the two Mn ions and plays an important role in the catalytic mechanism. Substitution of W96 with the unnatural amino acid 5-hydroxytryptophan leads to a persistent EPR signal which can be traced back to the neutral radical of 5-hydroxytryptophan with its hydroxyl proton removed. 5-Hydroxytryptophan acts as a hole sink preventing the formation of Mn(III) at the N-terminal active site and strongly suppresses enzymatic activity. The lower boundary of the standard reduction potential for the active site Mn(II)/Mn(III) couple can therefore be estimated as 740 mV against the normal hydrogen electrode at pH 4, the pH of maximum catalytic efficiency. Our results support the catalytic importance of long-range electron transfer in oxalate decarboxylase while at the same time highlighting the utility of unnatural amino acid incorporation and specifically the use of 5-hydroxytryptophan as an energetic sink for hole hopping to probe electron transfer in redox proteins.

Elucidating the Origin of Plasmon-Generated Hot Holes in Water Oxidation.

Plasmon-generated hot electrons in metal/oxide heterostructures have been used extensively for driving photochemistry. However, little is known about the origin of plasmon-generated hot holes in promoting photochemical reactions. Herein, we discover that, during the nonradiative plasmon decay, the interband excitation rather than the intraband excitation generates energetic hot holes that enable to drive the water oxidation at the Au/TiO2 interface. Distinct from lukewarm holes via the intraband excitation that only remain on Au, hot holes from the interband excitation are found to be transferred from Au into TiO2 and stabilized by surface oxygen atoms on TiO2, making them available to oxidize adsorbed water molecules. Taken together, our studies provide spectroscopic evidence to clarify the photophysical process for exciting plasmon-generated hot holes, unravel their atomic-level accumulation sites to maintain the strong oxidizing power in metal/oxide heterostructures, and affirm their crucial functions in governing photocatalytic oxidation reactions.

The absence of the queuosine tRNA modification leads to pleiotropic phenotypes revealing perturbations of metal and oxidative stress homeostasis in Escherichia coli K12.

Queuosine (Q) is a conserved hypermodification of the wobble base of tRNA containing GUN anticodons but the physiological consequences of Q deficiency are poorly understood in bacteria. This work combines transcriptomic, proteomic and physiological studies to characterize a Q-deficient Escherichia coli K12 MG1655 mutant. The absence of Q led to an increased resistance to nickel and cobalt, and to an increased sensitivity to cadmium, compared to the wild-type (WT) strain. Transcriptomic analysis of the WT and Q-deficient strains, grown in the presence and absence of nickel, revealed that the nickel transporter genes (nikABCDE) are downregulated in the Q- mutant, even when nickel is not added. This mutant is therefore primed to resist to high nickel levels. Downstream analysis of the transcriptomic data suggested that the absence of Q triggers an atypical oxidative stress response, confirmed by the detection of slightly elevated reactive oxygen species (ROS) levels in the mutant, increased sensitivity to hydrogen peroxide and paraquat, and a subtle growth phenotype in a strain prone to accumulation of ROS.

Prospective US investigational device exemption trial of a sutureless aortic bioprosthesis: One-year outcomes.

OBJECTIVES: We performed a prospective, single-arm clinical trial approved under a Food and Drug Administration Investigational Device Exemption to assess safety and efficacy of Perceval, a sutureless bovine pericardial aortic valve representing the initial US experience. METHODS: From June 2013 to January 2015, 300 patients (mean age 76.7 ± 7.7 years, 54.3% men, 37.3% ≥80 years, median Society of Thoracic Surgeons Predicted Risk of Mortality 2.8%), underwent Perceval valve implantation at 18 centers across the United States. Twenty patients (6.7%) had a bicuspid aortic valve and 5 (1.7%) patients had previous aortic valve replacement. A minimally invasive approach was used in 80 (26.7%) and concomitant procedures were performed in 113 (37.8%) patients. RESULTS: Two hundred eighty-nine patients (96.3%) were successfully implanted. Operative mortality (≤30 days) was 1.3% (n = 4) (observed to expected ratio of 0.40). One-year results included all-cause mortality in 5.2% (n = 15), stroke in 1% (n = 3), and endocarditis in 1.7% (n = 5). New permanent periprocedural pacemaker rate was 10.7% (n = 30/281); 2.5% (n = 7/281) resulted from third-degree atrioventricular block. One-year valve-related reoperation was 2.1% (n = 6). At 1-year follow-up, 98% of patients were in New York Heart Association class I/II, left ventricular mass index decreased from 103.5 ± 30.1 g/m2 at discharge to 95.8 ± 27.1 g/m2 (P = .001), and 3 (1.3%) moderate paravalvular leaks were identified. Health-related quality of life score increased from 62.7 ± 21.8 before surgery to 85.5 ± 17.8 at 1 year (P < .001). CONCLUSIONS: These results confirm the safety and effectiveness of the Perceval sutureless aortic valve replacement in study patients with lower mortality than expected from a risk prediction model. Persistent hemodynamic benefit and improvement in quality of life at 1 year support the importance of this device in the management of aortic valve disease.

Estimating the global conservation status of more than 15,000 Amazonian tree species.

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict that most of the world's >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century.

Hyperdominance in the Amazonian tree flora.

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.

Valoración previa a la inmunosupresión farmacológica en Reumatología / (Pre-assessment of pharmacological immunosuppression in Rheumatology)

ResumenEn los últimos 15 años se han desarrollado terapias y esquemas terapéuticos para inducir la remisión a la gran mayoría de enfermedades reumatológicas. La mejoría clínica lograda se consigue a expensas de una inmunosupresión más agresiva y específica, lo que conlleva un aumento en el riesgo de infecciones. La principal causa de muerte de las enfermedades autoinmunes, en los primeros 5 años de evolución, es la infección secundaria a la inmunosupresión. El objetivo del presente trabajo fue elaborar un documento de consenso con el afán de reducir este riesgo, basado en la mejor evidencia médica disponible, utilizando los recursos disponibles en el hospital para disminuir la morbimortalidad de los pacientes que reciben estas terapias. Contar con un documento de consenso permitirá minimizar los efectos secundarios y mejorar la acción terapéutica, con mayores oportunidades de remisión y una más adecuada utilización del recurso institucional.

AbstractIn the last 15 years therapies and therapeutic schemes have been developed to induce remission to the vast majority of rheumatologic diseases. The clinical improvement achieved is at the cost of a more aggressive and specific immunosuppression, which leads to an increase in the risk of infections. The main cause of death of autoimmune diseases in the first 5 years of evolution is infection secondary to immunosuppression. The objective of the present study was to develop a consensus document with the aim of reducing this risk of infection, based on the best available medical evidence, using the resources available in our hospital to reduce the morbidity and mortality of patients receiving these therapies. Having a consensus document will allow us to minimize side effects and improve therapeutic action with greater opportunities for referral and better utilization of institutional resources.

Potential contribution of open-cell stent design to balloon entrapment and review of techniques to recover.

Balloon entrapment during coronary angioplasty is a rare but potentially disastrous complication of percutaneous coronary intervention (PCI), described during both angioplasty alone, as well as with stents. This report describes the case of an entrapped stent-balloon within an extremely calcified proximal left anterior descending artery (LAD) lesion, and reviews techniques and strategies that can be applied in similar situations. In this case, we suspect the open-cell design of the specific stent used, combined with the high radial force of the calcified lesion, led to a "pincer effect," and entanglement of the balloon material within the stent scaffolding. After exhaustion of all percutaneous options to retrieve the balloon, the patient was ultimately taken for urgent cardiac surgery for extraction of the balloon and vein patch of the LAD.

Household arrangements of elderly persons in Brazil: analyses based on the national household survey sample (2009) / Arranjo domiciliar de idosos no Brasil: análises a partir da Pesquisa Nacional por Amostra de Domicílios (2009)

Introduction Increased longevity and, consequently, a rise in the number of elderly persons in Brazil, has an effect on different sectors, especially family living arrangements. Objective To analyze the socioeconomic profile of the family living arrangements of the elderly using PNAD micro-data (2009). Method A quantitative, descriptive, cross-sectional study using PNAD micro-data (2009) was performed. The elderly family living arrangements that constituted households in Brazil were analyzed. Results: The results indicated that the most representative arrangement was a couple who lived with their children and other relatives, followed by single parent units and couples with children. The head of household in most of the arrangements featuring a couple with children and other relatives was a man, while in one-person, single parent and mixed arrangements the head of household was more likely to be a woman. Conclusion Decisions regarding the type of family arrangement are attributed not only to the elderly individual and his or her family, but are the result of historical, sociocultural, political, economic and demographic factors, which may positive or negatively interfere with the quality of life of elderly persons.

Introdução O aumento da longevidade e, consequentemente, do número de idosos no Brasil, exerce influência em diversos setores, sendo um deles os arranjos domiciliares. Objetivo Analisar o perfil socioeconômico dos diferentes arranjos domiciliares de idosos no Brasil com base nos microdados da Pesquisa Nacional por Amostra de Domicílios (PNAD) de 2009. Método Estudo quantitativo, descritivo, com corte transversal, que utilizou os microdados da PNAD (2009), realizada pelo IBGE. O universo de análise foram os arranjos domiciliares de idosos que constituíam unidades domésticas e que viviam em todas as regiões brasileiras. Resultados Os resultados indicaram que o arranjo mais representativo foi o casal que mora com filhos e outros parentes, seguido pelo monoparental e pelo casal com filhos. A maioria dos arranjos casal com filhos e outros parentes é chefiada por homens, já nos arranjos unipessoal, monoparental e composto a chefia é feminina. Conclusão A decisão quanto ao tipo de arranjo domiciliar formado pelo idoso é uma decisão não só do idoso e de sua família, mas reflexo de uma série de fatores histórico, sociocultural, político, econômico e demográfico, podendo interferir positiva ou negativamente em sua qualidade de vida.

Epidemiología de la candidemia en el Hospital México / Candidemia and it's Epidemiology at Hospital México

Justificación y objetivos:las infecciones invasivas por Candida son frecuentes y de alta mortalidad en la práctica clínica. Existe poca información publicada al respecto en el país. Estudio retrospectivo y observacional que pretende aportar conocimiento novedoso sobre la epidemiología local de la candidemia.Métodos:se incluyó 136 pacientes mayores de 17 años en su primer episodio de candidemia, internados en el Hospital México, entre 2007 y 2010. Se realizó un análisis descriptivo y temporal, se evaluaron los factores asociados con C. parapsilosis y con la sobrevida a 30 días.Resultados:se detectó en promedio 34 episodios por año (rango 27 a 51), la incidencia acumulada fue de 1,1 casos/1000 admisiones. Las especies de Candida no albicans constituyeron el 62% de las levaduras aisladas. Exceptuando 2009, C. parapsilosis fue la especie predominante en 3 de 4 años estudiados (41%), seguida por C. albicans (38%). Se demostró una fuerte asociación entre la candidemia por C. parapsilosis, la presencia de catéter venoso central (OR=19,6, IC95%: 2,6 a 403,8, p<0,001) y el uso de nutrición parenteral (p=0,014). La mortalidad a 30 días fue del 46%. C. albicans mostró la mortalidad más alta y C. parapsilosis, la más baja. Los pacientes que no recibieron tratamiento antifúngico presentaron una probabilidad significativamente mayor de morir.Conclusiones:la elevada incidencia de candidemia por C. parapsilosisestá directamente relacionada con los catéteres venosos centrales y el uso de nutrición parenteral; su marcada reducción en la frecuencia durante 2009, merece ser investigada para dilucidar los factores que provocaron este cambio.

Background:Invasive Candida infections are frequent and exhibit high mortality in clinical practice. There are few published data in our country. This retrospective observational study intends to provide new knowledge about the local epidemiology of candidemia.Methods:136 patients older than 17 years were included when they had their first episode of candidemia during hospitalization at the Hospital Mexico, in the time period between 2007 and 2010. Descriptive and temporal analysis was performed and the risk factors associated with C. parapsilosis and survival were evaluated.Results:An average of 34 episodes of candidemia were recorded per year (range 27-51) and the cumulative incidence was 1.1 cases/1,000 admissions. The non-albicans Candida species accounted for 62% of the isolated yeasts, C. parapsilosis (41%) was the predominant yeast isolated in 3 out of the 4 years analized, except for 2009, followed by C. albicans (38%). Strong association between C. parapsilosis bloodstream infection, the presence of a central venous catheter (2.6 to 403.8, p <0.001 OR = 19.6, 95% CI) and use of parenteral nutrition (p=0.014) was established. The 30-day mortality was 46%, with C. albicans displaying the highest and C. parapsilosis the lowest. Patients who did not receive antifungal treatment had significantly higher mortality.Conclusions:the unusually high incidence of candidemia due to C. parapsilosis is directly related to the use of central venous catheters and parenteral nutrition; the marked reduction observed in 2009 needs further investigation to find out the causes of this change.

Patrones de distribución de especies arbóreas de dosel y sotobosque a escala local en bosques de tierra firme, Amazonia colombiana / Distribution patterns of canopy and understory tree species at local scale in a Tierra Firme forest, the Colombian Amazonia

The effect of environmental variation on the structure of tree communities in tropical forests is still under debate. There is evidence that in landscapes like Tierra Firme forest, where the environmental gradient decreases at a local level, the effect of soil on the distribution patterns of plant species is minimal, happens to be random or is due to biological processes. In contrast, in studies with different kinds of plants from tropical forests, a greater effect on floristic composition of varying soil and topography has been reported. To assess this, the current study was carried out in a permanent plot of ten hectares in the Amacayacu National Park, Colombian Amazonia. To run the analysis, floristic and environmental variations were obtained according to tree species abundance categories and growth forms. In order to quantify the role played by both environmental filtering and dispersal limitation, the variation of the spatial configuration was included. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the species distribution patterns. The spatial template was evaluated using the Principal Coordinates of Neighbor Matrix method. We recorded 14 074 individuals from 1 053 species and 80 families. The most abundant families were Myristicaceae, Moraceae, Meliaceae, Arecaceae and Lecythidaceae, coinciding with other studies from Northwest Amazonia. Beta diversity was relatively low within the plot. Soils were very poor, had high aluminum concentration and were predominantly clayey. The floristic differences explained along the ten hectares plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on Tierra Firme forests of Amacayacu National Park, and suggest reserve´s size as a key element to ensure the conservation of plant diversity at both regional and local levels.

El efecto de la variación ambiental en la estructura de las comunidades arbóreas en bosques tropicales, aún se debate. En paisajes como los bosques de tierra firme, donde el gradiente ambiental disminuye, el efecto de los suelos sobre los patrones de distribución de especies es mínimo. En contraste, un mayor efecto de la variación edáfica y topográfica sobre la composición florística, se ha reportado en estudios con diferentes tipos de plantas en bosques tropicales. Este estudio se realizó en diez hectáreas de una parcela permanente. Se evaluó el efecto de la variación ambiental y la configuración espacial sobre los patrones florísticos de las especies arbóreas a escala local, según el estado de desarrollo y categorías de abundancia relativa. Se registraron 14 074 individuos de 1 053 especies y 80 familias. Los suelos son ácidos, presentan altas concentraciones de Aluminio y son predominantemente arcillosos. La diversidad beta fue baja. Las diferencias florísticas explicadas fueron asociadas con procesos biológicos espacialmente estructurados, particularmente, con la limitación en dispersión. Aunque, la mayor parte de la variación no fue explicada por las variables consideradas. Estos resultados sugieren que procesos aleatorios son determinantes esenciales de la variación florística en bosques de tierra firme de la amazonia.

Variación florística de especies arbóreas a escala local en un bosque de tierra firme en la Amazonia colombiana / Floristic variation of canopy tree species at a local scale on tierra firme forests in Colombian Amazonia

El presente estudio se llevó a cabo en cinco hectáreas de una parcela permanente establecida en el Parque Nacional Amacayacu, Amazonia colombiana. En éste, se evaluó el efecto de la variación ambiental y la configuración espacial sobre los patrones florísticos de las especies arbóreas (DAP>10 cm) a escala local en un bosque de tierra firme. Se estudió la variación florística y ambiental en cuadrantes de 20x20 m. Adicionalmente, se consideraron diferentes categorías de abundancia (total, alta, media y baja). Se utilizó el Análisis de Correspondencia Linealizado y el Análisis de Correspondencia Canónica, seguido de una partición de la variación, para cuantificar la magnitud a la cual el ambiente y la limitación en dispersión determinan la variación florística. La fracción espacial, representando procesos de autocorrelación como la limitación en dispersión, se analizó mediante dos métodos: Asumiendo un polinomio de tercer grado y por el método de Coordenadas Principales de Matrices Vecinas (PCNM). La diversidad beta de la parcela fue baja. El PCNM aparece como el método de análisis más apropiado para estudios a esta escala. Las diferencias florísticas explicadas a lo largo de la parcela de 5-ha fueron principalmente asociadas con procesos biológicos como la limitación en dispersión. La mayor parte de la variación florística, no obstante, no fue explicada por las variables ambientales o espaciales consideradas. En conclusión, estos resultados sugieren que procesos aleatorios son determinantes esenciales de la variación espacial de las especies arbóreas a escala local en tierra firme en los bosques en el Parque Nacional Amacayacu.

This study was carried out in a 5-ha permanent plot established in the Amacayacu National Park, Colombian Amazonia. We assessed the extent at which floristic patterns of tree species were determined by either the environmental variation or the spatial configuration in tierra firme forests. Floristic and environmental variation was assessed on quadrants of 20x20 m. To run the analysis, four different categories of abundance (all, high, medium and low) were considered. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the patterns of species distribution in order to quantify the role played by both environmental filtering and dispersal limitation. The spatial template, which represents dispersal limitation, was evaluated in two different ways: using a third degree polynomial and using the Principal Coordinates of Neighbour Matrix (PCNM) method. Beta diversity was relatively low within the plot. PCNM appears as the most appropriate method to analyze the spatial template at this scale. The floristic differences explained along the 5-ha plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on tierra firme forests in the Amacayacu National Park.

Meningitis por Kluyvera sp. en una paciente con una derivación lumbo-peritoneal: reporte de un caso / Meningitis Kluyvera sp. in a patient with a lumboperitoneal derivation: report of a case

Describimos el caso de una paciente portadora de una derivación lumbo-peritoneal, que desarrolló una meningitis bacteriana en la cual Kluyvera sp. se aisló del líquido cefalorraquídeo. En nuestro conocimiento este es el primer caso reportado de infección del SNC por este microorganismo. Esta bacteria era sensible a cefalosporinas de tercera generación y se logró la resolución con Cefotaxime. El Género Kluyvera comprende tres especies infrecuentemente aisladas de muestras clínicas. Se puede asociar a infecciones desde leves a severas y posiblemente se favorece en un huésped inmunocomprometido.