Microbial communities in high altitude altiplanic wetlands in northern Chile: phytogeny, diversity and function

The phylogeny, diversity and function of microbial communities from several altiplanic wetlands was examined using an array of different but complimentary techniques. Results highlighted that microbial diversity exhibited a specific pattern in each wetland. Bacteria were dominant over Archaea in both freshwater and saline systems. Bacterial and archaeal diversity were both higher in sediment than in water samples. Lago Chungará, Laguna de Piacota and Bofedal de Parinacota are freshwater wetlands located at high altitude (>4400 m) in the north of Chile. They support microbial communities closely related to psychrophilic bacteria (e.g. Psychrobacter sp., Pseudomonas congelans, Flavobacterium psychrolimnae) in water and Proteobacteria and Actinobacteria in sediment samples. Salar de Huasco and Salar de Ascotán are located further south at an altitude of 3800 m and exhibit a wide range of salinities (varying between freshwater to 120 gL-1 of total dissolved salts). Microbial communities in these sites were characterized by bacteria tolerant to salt (e.g. halophilic Bacteria: Halomonas sp., halophilic Archaea: Halorubrum sp.). Cytophaga-Flavobacteria-Bacteroidetes was the most frequent group reported at the sites. In-depth studies focussing on the Salar de Huasco revealed a particular diversity of Archaea, characterized by a number of sequences related to uncultured groups and ammonia-oxidizing Crenarchaeota. Cyanobacteria from the Salar de Huasco were closely related to Cyanobacteria previously described from Antarctica. Isolates of halophilic bacteria and phototrophic bacteria displayed an elevated tolerance to different salt concentrations. The particular microbial diversity found in high altitude wetlands provides a new and exciting area of research

Bacterial Active Community Cycling in Response to Solar Radiation and Their Influence on Nutrient Changes in a High-Altitude Wetland

Indexación: Web of Science; Scopus.Microbial communities inhabiting high-altitude spring ecosystems are subjected to extreme changes in solar irradiance and temperature throughout the diel cycle. Here, using 16S rRNA gene tag pyrosequencing (cDNA) we determined the composition of actively transcribing bacteria from spring waters experimentally exposed through the day (morning, noon, and afternoon) to variable levels of solar radiation and light quality, and evaluated their influence on nutrient recycling. Solar irradiance, temperature, and changes in nutrient dynamics were associated with changes in the active bacterial community structure, predominantly by Cyanobacteria, Verrucomicrobia, Proteobacteria, and 35 other Phyla, including the recently described Candidate Phyla Radiation (e.g., Parcubacteria, Gracilibacteria, OP3, TM6, SR1). Diversity increased at noon, when the highest irradiances were measured (3.3-3.9 H', 1125 W m(-2)) compared to morning and afternoon (0.6-2.8 H'). This shift was associated with a decrease in the contribution to pyrolibraries by Cyanobacteria and an increase of Proteobacteria and other initially low frequently and rare bacteria phyla (< 0.5%) in the pyrolibraries. A potential increase in the activity of Cyanobacteria and other phototrophic groups, e.g., Rhodobacterales, was observed and associated with UVR, suggesting the presence of photo activated repair mechanisms to resist high levels of solar radiation. In addition, the percentage contribution of cyanobacterial sequences in the afternoon was similar to those recorded in the morning. The shifts in the contribution by Cyanobacteria also influenced the rate of change in nitrate, nitrite, and phosphate, highlighted by a high level of nitrate accumulation during hours of high radiation and temperature associated with nitrifying bacteria activity. We did not detect ammonia or nitrite oxidizing bacteria in situ, but both functional groups (Nitrosomona and Nitrospira) appeared mainly in pyrolibraries generated from dark incubations. In total, our results reveal that both the structure and the diversity of the active bacteria community was extremely dynamic through the day, and showed marked shifts in composition that influenced nutrient recycling, highlighting how abiotic variation affects potential ecosystem functioning.http://journal.frontiersin.org/article/10.3389/fmicb.2016.01823/ful

On the efficacy of stop-loss rules in the presence of overnight gaps

A stop-loss rule is a risk management tool whereby the investor predefines some condition that, upon being triggered by market dynamics, implies the liquidation of her outstanding position. Such a tool is widely used by practitioners in financial markets with the hope of improving their investment performance by cutting losses and consolidating gains. We analyze in this work the performance of four popular implementations of stop-loss rules applied to asset prices whose returns are modeled with consideration of overnight gaps, that is, jumps from the closing price of one day to the opening price of the next trading day. In addition, our models include acute momentary price drops (flash crashes), which are often believed to erode the performance gains that might be derived from stop-loss rules. For this analysis we consider different models of asset returns: random walk, autoregressive and regime-switching models. In addition, we test the performance of the considered stop-loss rules in a non-parametric, data-driven framework based on the stationary bootstrap. As a general conclusion we find that, even when including overnight gaps and flash crashes in our price models, in rising markets stop-loss rules improve the expected risk-adjusted return according to most metrics, while improving absolute expected return in falling markets. Furthermore, we find that in general the simple fixed percentage stop-loss rule may be, in risk-adjusted terms, the most powerful among the popular rules that this work considersPeer ReviewedPostprint (author's final draft

Determinacion de factores que se correlacionan con la especificidad de aloanticuerpos anti-eritrocitarios en donantes de sangre y pacientes del Hospital Regional de Talca. Período 2003-2005

42 p.Introducción: La aloinmunización después de la exposición a glóbulos rojos alogénicos depende de factores genéticos y adquiridos de la persona que ha sido expuesta, la dosis, la ruta de administración y la inmunogenicidad del antígeno, pero la cinética exacta sigue siendo desconocida. Materiales Y Métodos: Se revisaron los registros de los pacientes y donantes del Hospital Regional de Talca (HRT) a quienes se les había detectado anticuerpos irregulares. En el estudio fueron incluídas 12.275 donaciones efectivas, junto con los pacientes del HRT que fueron estudiados en el banco de sangre durante el período 2003-2005. La información requerida incluyó características demográficas (edad y sexo), procedencia para toda la población en estudio, para los donantes específicamente, incluyó tipo de donación (voluntario o de reposición), donante nuevo o con donaciones previas, mientras que para los pacientes incluyó servicio de procedencia y antecedentes de transfusión. Resultados: Tanto en donantes como en pacientes la aloinmunización predominó en el sexo femenino (80% y 84% respectivamente). Ocho pacientes, presentaron más de un aloanticuerpo a diferencia de los donantes aloinmunizados a quienes se les detectó sólo uno. El 77% de los pacientes que presentaron anticuerpos irregulares, no tenían antecedentes transfusionales asociados. La especificidad de los aloanticuerpos de mayor frecuencia entre los donantes fueron: anti-Lea (28%), anti D (20%), anti E (20%), anti K (16%) y entre los pacientes anti D (25%), anti E (18.8%), anti K (11.9%), anti Lea (11.3%). Mediante el análisis de Regresión Logística Binaria se determinó que anti-D se correlaciona con el sexo (p=0.043), al igual que anti-e (p=0.026), mientras que anti-E se relaciona con la edad (p=0.023). Conclusión: Tanto en donantes como en pacientes, la aloinmunización predominó en el sexo femenino. Los aloanticuerpos con mayor frecuencia fueron anti-Lea , anti D, anti E, anti K. Se ha determinado que la edad y el sexo son factores significativos en la especificidad de los anticuerpos. La condición de las personas estudiadas: donantes y pacientes, las transfusiones previas no fueron significativos para la especificidad de los aloanticuerpos encontrados

Microbial Activity Response to Solar Radiation across Contrasting Environmental Conditions in Salar de Huasco, Northern Chilean Altiplano

Indexación: Web of Science; Scopus.In high altitude environments, extreme levels of solar radiation and important differences of ionic concentrations over narrow spatial scales may modulate microbial activity. In Salar de Huasco, a high-altitude wetland in the Andean mountains, the high diversity of microbial communities has been characterized and associated with strong environmental variability. Communities that differed in light history and environmental conditions, such as nutrient concentrations and salinity from different spatial locations, were assessed for bacterial secondary production (BSP, H-3-leucine incorporation) response from short-term exposures to solar radiation. We sampled during austral spring seven stations categorized as: (a) source stations, with recently emerged groundwater (no-previous solar exposure); (b) stream running water stations; (c) stations connected to source waters but far downstream from source points; and (d) isolated ponds disconnected from ground sources or streams with a longer isolation and solar exposure history. Very high values of 0.25 mu E m(-2) s(-1), 72 W m(-2) and 12 W m(-2) were measured for PAR, UVA, and UVB incident solar radiation, respectively. The environmental factors measured formed two groups of stations reflected by principal component analyses (near to groundwater sources and isolated systems) where isolated ponds had the highest BSP and microbial abundance (35 microalgae taxa, picoeukaryotes, nanoflagellates, and bacteria) plus higher salinities and PO43- concentrations. BSP short-term response (4 h) to solar radiation was measured by H-3-leucine incorporation under four different solar conditions: full sun, no UVB, PAR, and dark. Microbial communities established in waters with the longest surface exposure (e.g., isolated ponds) had the lowest BSP response to solar radiation treatments, and thus were likely best adapted to solar radiation exposure contrary to ground source waters. These results support our light history (solar exposure) hypothesis where the more isolated the community is from ground water sources, the better adapted it is to solar radiation. We suggest that factors other than solar radiation (e.g., salinity, PO43-, NO3-) are also important in determining microbial productivity in heterogeneous environments such as the Salar de Huasco.http://journal.frontiersin.org/article/10.3389/fmicb.2016.01857/ful