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Anaerobic methane oxidation driven by microbial reduction of natural organic matter in a tropical wetland
Get PDF"Wetlands constitute the main natural source of methane on Earth due to their high content of natural organic matter (NOM), but key drivers, such as electron acceptors, supporting methanotrophic activities in these habitats are poorly understood. We performed anoxic incubations using freshly collected sediment, along with water samples harvested from a tropical wetland, amended with C-13-methane (0.67 atm) to test the capacity of its microbial community to perform anaerobic oxidation of methane (AOM) linked to the reduction of the humic fraction of its NOM. Collected evidence demonstrates that electron-accepting functional groups (e.g., quinones) present in NOM fueled AOM by serving as a terminal electron acceptor. Indeed, while sulfate reduction was the predominant process, accounting for up to 42.5% of the AOM activities, the microbial reduction of NOM concomitantly occurred. Furthermore, enrichment of wetland sediment with external NOM provided a complementary electron-accepting capacity, of which reduction accounted for similar to 100 nmol (CH4)-C-13 oxidized center dot cm(3)center dot day(1). Spectroscopic evidence showed that quinone moieties were heterogeneously distributed in the wetland sediment, and their reduction occurred during the course of AOM. Moreover, an enrichment derived from wetland sediments performing AOM linked to NOM reduction stoichiometrically oxidized methane coupled to the reduction of the humic analogue anthraquinone-2,6-disulfonate. Microbial populations potentially involved in AOM coupled to microbial reduction of NOM were dominated by divergent biota from putative AOM-associated archaea. We estimate that this microbial process potentially contributes to the suppression of up to 114 teragrams (Tg) of CH(4 center dot)year(-1) in coastal wetlands and more than 1,300 Tg center dot year(-1), considering the global wetland area.
Efecto de factores abióticos y bióticos sobre la estructura de la comunidad microbiana del suelo en un ambiente oligotrófico
Get PDF"En los suelos, las comunidades de microorganismos están sujetas a la variación de factores abióticos e interacciones bióticas que existen entre ellos y otros organismos. Nuestra hipótesis se basa en que debido a las condiciones que presentan las zonas áridas, se espera una mayor influencia de los procesos deterministas en la estructuración de las comunidades, entonces entre mayor sea la similitud en las características ambientales, habrá una mayor similitud en la composición y estructura de las comunidades microbianas. El objetivo de este trabajo fue determinar cómo los factores abióticos (propiedades fisicoquímicas del suelo y estacionalidad, refiriéndose a lluvias y sequías), así como interacciones bióticas (planta-microorganismos y microorganismos-microorganismos), son factores de selección dándole forma a las comunidades microbianas, especialmente en zonas áridas oligotróficas. En este trabajo se llevaron a cabo dos muestreos de las comunidades rizosféricas del Agave lechuguilla y de interespacios libres de vegetación, uno en temporada de secas y otro de lluvias, en cuatro sitios en el valle de Cuatro Ciénegas en Coahuila. Se secuenció el gen 16S rRNA por Illumina para la caracterización de las comunidades microbianas y para el suelo se determinó el carbono y nitrógeno total, pH, conductividad, humedad, materia orgánica, calcio, magnesio, sodio, potasio, amonio, nitrato y fósforo. Nuestros resultados muestran diferencias significativas tanto en las propiedades fisicoquímicas del suelo como en la composición microbiana de la rizósfera e interespacios, las cuales se acentúan en época de secas. También muestran una relación entre el pH, la conductividad, humedad, materia orgánica y relación C/N con la comunidad microbiana. Por último, entre algunos grupos microbianos persistieron interacciones que se presentaron en todas las condiciones (rizósfera, interespacio, secas y lluvias), una correlación negativa entre Actinobacteria contra Bacteroidetes y Proteobacteria y una correlación positiva entre Bacteroidetes con Proteobacteria y Verrucomicrobia. ""In soils, communities of microorganisms are subjected to the variation of abiotic factors and biotic interactions that exist between them and other organisms. Our hypothesis is based on the fact that due to the conditions presented by arid zones, is expected a higher influence of deterministic processes in community assembly, then, higher similarity in the environmental conditions will lead to higher similarity in the composition and structure of microbial communities. The objective of this work was to determine how abiotic factors (soil physicochemical properties and seasonality) as well as biotic interactions (plant-microorganisms and microorganisms-microorganisms), are selection factors shaping microbial communities, especially in oligotrophic arid zones. In this work we carry out two samplings of rhizospheric communities from Agave lechuguilla and from vegetation-free bulk soil, one of these samplings was in dry season and the other one in rainy season, at four sites of Cuatro Ciénegas valley in the state of Coahuila. 16S rRNA gene was amplified and sequenced by Illumina to characterize microbial community, for soil samples was determined total carbon and nitrogen, pH, conductivity, moisture, organic matter, calcium, magnesium, sodium, potassium, ammonium, nitrate and phosphorus. Our results show significant differences between rhizosphere and bulk soil community composition and soil physicochemical properties, such differences were accentuated in dry season. Furthermore, our results also show that pH, conductivity, moisture, organic matter and C/N ratio are related to the bacterial community. Finally, between some microbial groups there were some interactions that persisted in all conditions (rhizosphere, bulk soil, dry and rainy season), a negative correlation between Actinobacteria against Bacteroidetes and Proteobacteria and a positive correlation between Bacteroidetes with Proteobacteria and Verrucomicrobia
Índice de pobreza del agua en los acuíferos de Cerritos-Vila Juárez y Rioverde de la zona media de San Luis Potosí
Get PDF"En la actualidad la deficiente gestión de los recursos hídricos, el crecimiento de la población y una falta cultura en aprovechamiento de los recursos naturales, ha incrementado la sobreexplotación de los acuíferos en nuestro país y como consecuencia en los últimos 55 años, la disponibilidad anual de agua ha disminuido un 62%. El Índice de Pobreza del Agua (IPA) es una herramienta multidisciplinaria que nos ayuda a cuantificar la pobreza de hídrica e identificar los componentes que requieren una mayor atención. Esta metodología se basa en la sumatoria ponderada de seis componentes (recurso, acceso, capacidad, uso, calidad del agua y ambiente), incluyendo en su evaluación parámetros fisicoquímicos y socioeconómicos. Su escala de valores esta entre 0 y 1. La metodología fue aplicada en los municipios que comprenden los acuíferos de Cerritos-Villa Juárez y Rioverde, en donde el 84% del agua que se extrae es para uso agrícola, esta actividad tienen un impacto económico muy significativo ya que la mayor parte de los ingresos de la región dependen de la misma. En la aplicación de este índice, se desarrolló una nueva metodología para el cálculo del componente ambiente, con base en el uso de Percepción Remota utilizando imágenes satelitales Landsat 7, para generar un arreglo de datos que integran un mapa espaciotemporal de la cobertura vegetal en el área de estudio, con lo cual podemos evaluar el impacto que se tiene en el recurso y el medio ambiente. El valor promedio obtenido del IPA es de 0.66, de los seis componentes evaluados, el valor más alto (0.77) pertenece al componente ambiente, mientras el más bajo corresponde al componente Uso (0.43). Aunque hay una gran disponibilidad del recurso hídrico, la calidad del agua para consumo humano es un problema grave en la región.
A review of definitions of the Himalayan Main Central Thrust
Get PDF"Most workers regard the Main Central Thrust (MCT) as one of the key high strain zones in the Himalaya because it accommodated at least 90 km of shortening, because that shortening exhumed and buried hanging wall and footwall rocks, and due to geometric and kinematic connections between the Main Central Thrust and the structurally overlying South Tibet Detachment. Geologists currently employ three unrelated definitions of the MCT: metamorphic-rheological, age of motion-structural, or protolith boundary-structural. These disparate definitions generate map and cross-section MCT positions that vary by up to 5 km of structural distance. The lack of consensus and consequent shifting locations impede advances in our understanding of the tectonic development of the orogen. Here, I review pros and cons of the three MCT definitions in current use. None of these definitions is flawless. The metamorphic-rheological and age of motion-structural definitions routinely fail throughout the orogen, whereas the protolith boundary-structural definition may fail only in rare cases, all limited to sectors of the eastern Himalaya. Accordingly, a definition based on high strain zone geometry and kinematics combined with identification of a protolith boundary is the best working definition of the MCT.
Diversification of transcriptional regulation determines subfunctionalization of paralogous branched chain aminotransferases in the yeast Saccharomyces cerevisiae
Get PDF"Saccharomyces cerevisiae harbors BAT1 and BAT2 paralogous genes that encode branched chain aminotransferases and have opposed expression profiles and physiological roles . Accordingly, in primary nitrogen sources such as glutamine, BAT1 expression is induced, supporting Bat1-dependent valine–isoleucine–leucine (VIL) biosynthesis, while BAT2 expression is repressed. Conversely, in the presence of VIL as the sole nitrogen source, BAT1 expression is hindered while that of BAT2 is activated, resulting in Bat2-dependent VIL catabolism. The presented results confirm that BAT1 expression is determined by transcriptional activation through the action of the Leu3–?-isopropylmalate (?-IPM) active isoform, and uncovers the existence of a novel ?-IPM biosynthetic pathway operating in a put3? mutant grown on VIL, through Bat2-Leu2-Leu1 consecutive action. The classic ?-IPM biosynthetic route operates in glutamine through the action of the leucine-sensitive ?-IPM synthases. The presented results also show that BAT2 repression in glutamine can be alleviated in a ure2? mutant or through Gcn4-dependent transcriptional activation. Thus, when S. cerevisiae is grown on glutamine, VIL biosynthesis is predominant and is preferentially achieved through BAT1; while on VIL as the sole nitrogen source, catabolism prevails and is mainly afforded by BAT2.
Hetero- and homodimerization of Arabidopsis thaliana arginine decarboxylase AtADC1 and AtADC2
Get PDF"The arginine decarboxylase enzyme (ADC) carries out the production of agmatine from arginine, which is the precursor of the first polyamine (PA) known as putrescine; subsequently, putrescine is turned into the higher PAs, spermidine and spermine. In Arabidopsis thaliana PA production occurs only from arginine and this step is initiated by two ADC paralogues, AtADC1 and AtADC2. PA production is essential for A. thaliana life cycle. Here, we analyzed the sub-cellular localization of AtADC1 and AtADC2 enzymes through GFP translational fusions. Our data revealed that the A. thaliana arginine decarboxylase enzymes exhibit a dual sub-cellular localization both in the cytosol and chloroplast. Moreover, we examined the protein dimer assembly using a Bimolecular Fluorescence Complementation (BiFC) approach, which showed that AtADC1 and AtADC2 proteins were able to form homodimers in the cytosol and chloroplast. Interestingly, we found the formation of AtADC1/AtADC2 heterodimers with similar sub-cellular localization than homodimers. This study reveals that both ADC proteins are located in the same cell compartments, and they are able to form protein interaction complexes with each other.
A review of Himalayan stratigraphy, magmatism, and structure
Get PDF"The Himalayan Orogen consists of two rock packages that parallel the topographic trend of the mountain belt between the eastern and western syntaxes. To avoid confusion with appellations previously used to identify elevation, Cenozoic metamorphic grade, or Cenozoic structural position, in this paper I introduce new names for these rock packages: Himalayan Assemblage A and Himalayan Assemblage B. Inclusion in an assemblage signifies that there was physical contiguity between adjacent members of the assemblage at the time of deposition or intrusion. Assemblage A and Assemblage B may not have shared depositional or intrusive relationships prior to Early Cretaceous time.
Himalayan Assemblage A mostly consists of sedimentary rocks deposited on the northern margin of India; the depositional substrate for these strata is not exposed anywhere in the orogen. Assemblage A comprises three main groups of rocks divided based on age of deposition or intrusion: Paleoproterozoic to Early Mesoproterozoic, Late Carboniferous to Permian, and terminal Cretaceous to Pleistocene. The oldest rocks exposed in the Himalaya, ca. 1900-1800 Ma clastic deposits and the ca. 1880-1830 Ma granite and gabbro that intruded them, may have formed in a continental rift setting. This rift system established depositional strike toward the northeast, at a high angle to the strike of Cenozoic thrusts in the western Himalaya, with obliquity decreasing eastward. The succeeding Upper Paleoproterozoic to Lower Mesoproterozoic strata were deposited in a passive margin setting or, alternatively, in an epi-cratonic basin. Upper Carboniferous to Permian strata are called the Gondwana Group; these deposits are present only in the eastern half of the orogen. This package is dominantly clastic and probably was deposited in extensional basins related to the breakup of Pangea. Depositional strike of the Gondwana Group was likely between 25 degrees and 50 degrees west of north. Upper Paleocene to Pleistocene, dominantly clastic, strata were deposited in the Himalayan foreland basin. Along the central two-thirds of the orogen, depositional age uncertainties extend the possible depositional ages of the lowermost of these strata into the latest Cretaceous Period.
Carbon sponge-type nanostructures based on coaxial nitrogen-doped multiwalled carbon nanotubes grown by CVD using benzylamine as precursor
Get PDF"Carbon sponges-type nanostructures (CSTN) based on coaxial nitrogen-doped multiwalled carbon nanotubes (CA-MWCNTs) were synthesized using the aerosol assisted chemical vapor deposition method involving the decomposition of a mixture of ferrocene, benzylamine, thiophene, and ethanol at 1020 °C under a flow of H2/Ar. Sample morphology and composition profiles were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). SEM and TEM characterizations demonstrated that the CA-MWCNTs consisted of a core MWCNT surrounded by graphite materials with low crystallinity which was confirmed by XRD and Raman spectroscopy. Depending where the CSTN were collected along the reactor, three types of core MWCNTs morphologies were found: (1) N-doped MWCNTs with a bamboo shape and zigzagged growth, (2) straight MWCNTs, and (3) wavy MWCNTs. The carbon CSTN showed to be highly hydrophobic with outstanding oil absorption properties. XPS characterizations suggest the presence of water-fearing chemical groups such as ester- and ethoxy-groups anchored on the surface of the CA-MWCNTs. The mechanism in which the three types of MWCNTs are formed, the nature of the shell disordered graphite materials, and the hydrophobicity of the carbon sponges-type are thoroughly discussed.
Obtención de membranas poliméricas para celdas de poder
Get PDFTesis (Maestría en Nanociencias y Materiales)"Las crecientes preocupaciones sobre el agotamiento de recursos energéticos derivados de los combustibles fósiles, y el problema de cambio climático asociados a éstos, han impulsado la búsqueda de diferentes alternativas de producción energética. Como consecuencia de ello, las celdas de combustible con membrana intercambiadora de protones (PEMFC, por sus siglas en inglés) han causado un gran impacto, debido a su eficiencia energética y la nula emisión de contaminantes al medio ambiente durante su funcionamiento.
Los polímeros sulfonados han sido considerados como una adecuada alternativa a los polímeros perfluorados para la obtención de membranas de intercambio protónico en celdas de combustible. Actualmente, el Nafion es el polímero perfluorado comercial más utilizado para dicha aplicación; sin embargo, el elevado costo, el límite en la temperatura de funcionamiento y la baja estabilidad química son problemas serios que ha presentado este tipo de polímero.
En este contexto, la investigación realizada en este trabajo fue acerca de la sulfonación, obtención y caracterización de membranas de polisulfona, así como la incorporación de óxido de grafeno a éstas, con la posible aplicación en celdas de poder.
En términos de la sulfonación, se evaluó el efecto de la relación molar entre el polímero y el agente sulfonante (ácido clorosulfónico) sobre el porcentaje de sulfonación logrado. La relación molar que brindó el mayor grado de sulfonación (63%) fue de 1:1. Por encima de dicha relación no fue posible generar membranas, ya que la solubilidad del polímero sulfonado se incrementó drásticamente, aunado al rompimiento de cadena generado por la reacción de sulfonación.
Se evaluaron diferentes propiedades de los materiales obtenidos, tales como las mecánicas (módulo de Young, esfuerzo máximo a la tensión y deformación al rompimiento); térmicas (resistencia térmica y transiciones térmicas) y la capacidad de intercambio iónico; siendo el parámetro de mayor interés la capacidad de intercambio iónico, IEC (Ion Exchange Capacity, por sus siglas en inglés) de las membranas poliméricas generadas, ya que es una especificación importante de los polímeros comerciales para dicha aplicación. En este sentido, se logró obtener una membrana de polisulfona sulfonada con un valor de IEC (1.31 meq/g) ligeramente mayor al del polímero comercial Nafion® 117 (1.02 meq/g).
Por otro lado, la adición de óxido de grafeno a la matriz polimérica sulfonada, incrementó sus propiedades mecánicas, tales como el módulo de Young, la deformación al rompimiento y el esfuerzo máximo a la tensión; las cuales habían sido reducidas por el proceso de sulfonación debido a la alta oxidación que posee el agente sulfonante sobre la polisulfona. Sin embargo, la presencia de los grupos epoxi, hidroxilo y carboxilo, que se encuentran en la superficie del óxido de grafeno interactúan con los grupos ácido sulfónico, lo que provoca que disminuya la hidrofilicidad de las membranas, propiedad importante para la conducción protónica en una celda de poder.
En cuanto a la resistencia térmica de los materiales generados, la sulfonación y la presencia del óxido de grafeno, modificaron ésta de forma antagónica. A mayor grado de sulfonación menor resistencia térmica, y a mayor contenido de óxido de grafeno, mayor resistencia térmica. Por lo que es posible contrarrestar el efecto negativo de la sulfonación sobre dicha propiedad.""The growing concerns about the depletion of energy resources derived from fossil fuels, and the associated climate change problem, have driven the search for alternative energy production alternatives. As a result, proton exchange membrane fuel cells (PEMFC) have made a big impact, due to their energy efficiency and the emission of no pollutants to the environment during their operation.
Sulfonated polymers have been considered as an adequate alternative to perfluorinated polymers for the production of proton exchange membranes in fuel cells. Currently, Nafion is the most widely used commercial perfluorinated polymer for such application. However, the high cost, the limit in the operating temperature and the low chemical stability are serious problems that this type of polymer has presented.
In this context, the research carried out in this work was about the sulfonation, generation and characterization of polysulfone membranes, as well as the incorporation of graphene oxide to these, with the possible application in fuel cells.
In terms of sulfonation, the effect of the molar ratio between the polymer and the sulfonating agent (chlorosulfonic acid) on the achieved percentage of sulfonation was evaluated. The molar ratio that provided the highest degree of sulfonation (63%) was 1: 1. Above this relationship it was not possible to generate membranes, since the solubility of the sulfonated polymer increased drastically, coupled with the chain breakage generated by the sulfonation reaction.
Different properties of the obtained materials, such as mechanical behavior (Young's modulus, tensile strength and deformation at break), and thermal (thermal resistance and thermal transitions) were evaluated; along with the ion exchange capacity. The most interesting parameter being the ion exchange capacity (IEC) of the polymer membranes generated, since it is a specification for commercial polymers for such application. In this sense, a sulfonated polysulfone membrane with a slightly higher IEC value (1.31 meq/g) than the commercial Nafion® 117 polymer (1.02 meq/g) was obtained.
On the other hand, the addition of graphene oxide to the sulfonated polymer matrix increased its mechanical properties, such as the Young's modulus, the deformation at break and the tensile strenght; wich had been reduced by the sulfonation process due to the high oxidation of the sulfonating agent on the polysulfone. However, the presence of the epoxy, hydroxyl and carboxyl groups found on the surface of the graphene oxide interact with the sulfonic acid groups, which causes a decrease in the hydrophilicity of the membranes, an important property for proton conduction in a fuel cell.
As for the thermal resistance of the materials generated, the sulfonation and the presence of the graphene oxide modified the latter in an antagonistic way. The higher the degree of sulfonation the lower the thermal resistance, and the higher the content of graphene oxide, the higher the thermal resistance. Therefore, it is possible to counteract the negative effect of sulfonation on said property.
Infinite families of hyperbolic prime knots with alternation number 1 and dealternating number n
Get PDF"For each positive integer n we will construct a family of infinitely many hyperbolic prime knots with alternation number 1, dealternating number equal to n, braid index equal to n+3 and Turaev genus equal to n.