http://hdl.handle.net/11627/2 Sun, 05 Apr 2026 12:50:18 GMT 2026-04-05T12:50:18Z http://hdl.handle.net/11627/6756 Versatilidad metabólica de una comunidad arseniato reductora bajo condiciones reductoras y oxidantes Treviño Calderón, Katia Karime "El arsénico es un metaloide tóxico para todos los seres vivos, en humanos puede causar daños severos a la salud. Para la biorremediación de sitios contaminados con arsénico se pueden usar bacterias con capacidad de respirar arsénico, que usan arseniato como aceptor final de electrones para transformarlo en arsenito, en combinación con bacterias que reducen sulfato a sulfuro. El arsenito y el sulfuro al alcanzar la saturación precipitan como sulfuros de arsénico (biominerales) y de esta forma separan el arsénico de la corriente acuosa para su confinación, disposición o reúso. Sin embargo, se ha perdido de vista que existe el riesgo de que el arsénico de los sulfuros de arsénico se movilice nuevamente por la acción de bacterias quimiolitótrofas capaces de usar arsenito como donador de electrones para la fijación de CO2 mediante la reducción de oxígeno o nitrato. Actualmente no hay investigación sobre dicho tema. El objetivo de este proyecto fue evaluar la capacidad de un consorcio especializado en arseniato reducción para movilizar arsénico de sulfuros de arsénico biogénicos, al oxidar arsenito en condiciones aerobias o anóxicas. En primer lugar, se evaluaron las cinéticas de reducción de arseniato y la posterior oxidación del arsenito producido en ensayos de microcosmos en lote por triplicado conteniendo 10 mM de arseniato. Los resultados mostraron que tanto la reducción de arseniato como la oxidación de arsenito fueron llevadas a cabo por el mismo consorcio anaerobio que se usó como inóculo en los ensayos. Dicho consorcio había sido previamente enriquecido y usado exclusivamente para llevar a cabo la reducción de arseniato y sulfato con lactato como donador de electrones en condiciones anaerobias. En otro conjunto de ensayos, se usaron precipitados de sulfuros de arsénico para evaluar la capacidad de la comunidad para movilizar nuevamente el arsénico a la fase acuosa. En este caso se encontró que la capacidad de oxidar arsenito fue 7 veces menor que en los ensayos con arsénico soluble. El consorcio microbiano con el que se realizaron los ensayos estaba compuesto por géneros como Desulfomicrobium, Desulfobulbus y Desulfosporosinus. Después de la etapa de oxidación, la diversidad disminuyó entre 38.8 y 68.2% para experimentos inoculados y endógenos, respectivamente; mientras que géneros como Thauera y Pseudomonas se enriquecieron entre 55- 83% y 85-95%, respectivamente. Estos resultados demuestran que los consorcios microbianos arseniato reductores poseen dualidad metabólica y son capaces de realizar el proceso contrario (oxidación de arsenito). Por lo tanto, los bioprecipitados de sulfuros de arsénico obtenidos mediante un proceso de biorremediación anaerobio podrían perder su estabilidad al encontrarse bajo condiciones fluctuantes en el ambiente (óxicas/anóxicas)."; "Arsenic is a toxic metalloid for all living organisms; in humans it can cause severe health damage. For the bioremediation of arsenic-contaminated sites, bacteria with the ability to respire arsenic can be used, which use arsenate as the final electron acceptor to transform it into arsenite, in combination with bacteria that reduce sulfate to sulfide. When arsenite and sulfide reach saturation, they precipitate as arsenic sulfides (biominerals), and in this way arsenic is separated from the aqueous stream for confinement, disposal, or reuse. However, it has been overlooked that there is a risk that arsenic from arsenic sulfides may become mobilized again by the action of chemolithotrophic bacteria capable of using arsenite as an electron donor for CO₂ fixation through oxygen or nitrate reduction. Currently, there is no research on this topic. The objective of this project was to evaluate the capacity of an arsenatereducing specialized consortium to mobilize arsenic from biogenic arsenic sulfides by oxidizing arsenite under aerobic or anoxic conditions. First, the kinetics of arsenate reduction and the subsequent oxidation of the produced arsenite were evaluated in triplicate batch microcosm assays containing 10 mM arsenate. The results showed that both arsenate reduction and arsenite oxidation were carried out by the same anaerobic consortium used as inoculum in the assays. This consortium had been previously enriched and used exclusively to carry out arsenate and sulfate reduction with lactate as electron donor under anaerobic conditions. In another set of assays, arsenic sulfide precipitates were used to evaluate the community’s ability to mobilize arsenic again into the aqueous phase. In this case, it was found that the capacity to oxidize arsenite was 7 times lower than in assays with soluble arsenic. The microbial consortium used in the assays was composed of genera such as Desulfomicrobium, Desulfobulbus, and Desulfosporosinus. After the oxidation stage, diversity decreased between 38.8 and 68.2% for inoculated and endogenous experiments, respectively; while genera such as Thauera and Pseudomonas were enriched between 55–83% and 85–95%, respectively. These results demonstrate that arsenate-reducing microbial consortia possess metabolic duality and can perform the opposite process (arsenite oxidation). Therefore, arsenic sulfide bioprecipitates obtained through an anaerobic bioremediation process could lose their stability when found under fluctuating environmental conditions (oxic/anoxic)." Thu, 19 Mar 2026 00:00:00 GMT http://hdl.handle.net/11627/6756 2026-03-19T00:00:00Z http://hdl.handle.net/11627/6677 Social-ecological participatory observatory sites in arid northern Mexico: co-definition of shared space and future challenges of drought under climate change ESQUIVEL-ARRIAGA, GERARDO Drylands social-ecological systems are one of the most extensive, diverse, yet highly vulnerable social–ecological systems of our planet Earth. Aridity and drought patterns cause increasing pressure on land and water resources and are some of the largest global and local environmental and social change problems and thus are a challenge for science and society. Drylands cover approximately 65% of the Mexican territory; over 60% of the total population inhabit these areas. Recent scientific consensus suggests that to potential solutions to land degradation need to be identified and implemented within the context of local environmental, social, economic and political conditions. At the same time, the complexity of drought risk demands cross-sectoral policies accounting for regional diversity, leveraging local knowledge and promoting communities' engagement. In this research, our study sites, the Social-ecological participatory observatories (OPSEs) lie along a west–east transect in northern Mexico drylands. The OPSEs are a social-ecological innovation and provide a space for the consolidation of formal and informal alliances for sustainability through learning communities that share diverse knowledge, technologies, and innovations. As a result of a survey applied to actors of various sectors linked to the OPSEs, priority issues were defined, including climate change, drought, and water scarcity. In this research, the general objective was to analyze the social-environmental value linked to shared land by multiple stakeholders as a basis to co-define the spatial boundaries of social-ecological systems and analyze potential future changes in precipitation and the potential occurrence of droughts under climate change conditions in the context of the OPSE network divided in three chapters. Chapter one showed that the valuation of land by multiple stakeholders by identifying and mapping different meaningful places in the OPSE Mapimí can be integrated to generate socio-economic variables that are not available in vectorial format and combined with biophysical variables allowed the spatial delineation of a Social-ecological system and the estimation of social-ecological units within the OPSE Mapimí. This delineation is dynamic and flexible and subject to updates and re-evaluations, as it is based on the perception, intuition, experience, interest, knowledge and judgment of different stakeholder groups, which are highly experienced and knowledgeable about the local and current social-environmental conditions. Chapter 2 highlights that for an adequate characterization of drought conditions, good quality precipitation data are indispensable. This chapter examined how the rainfall gauge network in Mexico’s drylands that is highly heterogeneously distributed and frequently with incomplete datasets, can be compensated by information derived from global precipitation datasets. Based on the performance of five global precipitation datasets, we suggest using CHIRPS and AgERA5 climatic data to fill gaps of observational rain gauge information. Chapter 3 examined the occurrence (frequency, severity and duration) of historical (1981-2010) and future (2041-2100) meteorological droughts at time scale of 12 months for the OPSEs network using the Standardized Precipitation Index (SPI). Likewise, the perception of the concept of drought and adaptation measures were analyzed in the OPSE Mapimí. Results suggest that in the near (2041-2070) and far (2071-2100) future, an increase in the average annual precipitation is projected for the OPSE network. In general, drought conditions at the 12-months time scale for the near future, presented less frequent events with a decrease in its duration. In the OPSE Mapimí, the drought concept mostly found to be linked with issues related to rainfall (no rain) and vegetation (no forage). The years 1951, 1953, 1970, 1972, 1977, 1978, 1984, 1986, 1988, 1989, 1990, 1995, 1997, 1998, 2001, 2002, 2008, 2011, 2012 and 2019 were identified as the most important drought events since they affected their living conditions. The years 1958, 1987, 1990 and 2010 were identified as the wettest years, causing flooding in the ejido Laguna de Palomas. Changes in the weather were generally recognized by the respondents (more heat and less rain), if not expressed as “climate change”. Adaptation measures to face drought in case of cattle raising include selling some animals to maintain the remaining animals or cutting and burning prickly pear as an alternative food source for livestock. The salt producers and ecotourism people were temporarily employed or received economic support from relatives. One of the innovations of this research is that the process promotes an exchange of information (scientific and non-scientific) and is approached from two different perspectives: one based on observation and measurement (e.g., relief morphometry, land use/cover, etc.) and a phenomenological one, based mainly on people's experiences (mapping of significant places from valuations of space by multiple sectors and the deep understanding of the concept drought. Hence, this research represents a transferable and replicable approach. The OPSE model, in a time frame of 4-5 years (to be defined), is observed to have important implications for future transdisciplinary research that could focus on collaborative social-environmental governance with the important focus on water governance, climate modeling, community resilience and novel questions that could lead to the development of more sustainable approaches for the adaptive and integral management of Mexico’s drylands. Tue, 22 Apr 2025 00:00:00 GMT http://hdl.handle.net/11627/6677 2025-04-22T00:00:00Z http://hdl.handle.net/11627/6663 Precipitación de sulfuros de arsénico en un sistema biológico-fisicoquímico Brito García, Consuelo "La contaminación por arsénico en el agua representa un alto riesgo para la salud humana y el medio ambiente. La OMS establece un límite máximo permisible de 10 ?g/L en agua para consumo humano. En México, altas concentraciones de arsénico son comunes en acuíferos y zonas mineras como por ejemplo Matehuala, S.L.P., con niveles de hasta 158 mg/L en agua. Los métodos de tratamiento existentes como la filtración y la precipitación química son costosos y generan subproductos tóxicos. La remediación biológica, la cual aprovecha la capacidad metabólica de las bacterias arseniato- y sulfato-reductoras, ofrece una alternativa prometedora para la remoción del arsénico mediante su biomineralización o formación de fases minerales de sulfuros de arsénico. El objetivo del presente estudio fue evaluar la precipitación de sulfuros de arsénico en un sistema biológico-fisicoquímico para la remoción de arsénico del agua. Se caracterizaron las actividades biológicas (arseniato- y sulfato-reductora) de un consorcio recuperado de sitios contaminados. Posteriormente se operó un reactor de lecho fijo en lote (volumen de trabajo 250 mL) con las dos actividades acopladas y se eliminó con éxito hasta 99% del arseniato (2.5 mM) y 100% del sulfato (hasta 5 mM) utilizando lactato como donador de electrones. Los precipitados biogénicos contenían principalmente sulfuros de arsénico (AsS) en estructuras similares a fibras. A partir del soporte del primer reactor, se pusieron en marcha dos reactores en continuo (500 mL c/u) con actividades por separado. En el reactor arseniato-reductor se logró una eficiencia de reducción superior a 85%, mientras que en el reactor sulfato-reductor se logró remover hasta 80% del sulfato alimentado. A partir de los efluentes de ambos reactores se evaluó el efecto de las relaciones molares y el pH en la precipitación de sulfuros de arsénico, mediante experimentos en lote con diferentes relaciones molares de S:As (1.4, 2.7, 5.4) y pH (2, 5 y 6). Los resultados mostraron un mayor porcentaje de remoción del arsénico (93%) a pH 2 en el plazo de una hora y menor eficiencia de eliminación (19-64%) a pH 6. Finalmente se operó un reactor de precipitación a relación molar S:As 1.5 a pH 2 y 5. Se encontró que a pH 2, los precipitados de arsénico se solubilizan después de 48 horas, mientras que a pH 5, los precipitados fueron más estables, logrando una remoción de hasta 92% en cinco días. Finalmente, los análisis de MEB-EDS indicaron que el precipitado obtenido a pH 2 estaba compuesto por S y As, en una relación molar 1.6 (S:As). El precipitado presentó morfología esférica con partículas entre 118 a 280 nm. El patrón de difracción de rayos X (XRD) confirmó la presencia de fases cristalinas de oropimente (As2S3) y rejalgar (As4S4). Con respecto al precipitado que se obtuvo con pH 5, la micrografía de MEB mostró una morfología de partículas prismáticas con tamaño entre 1.7 a 3 µm. Los resultados de EDS indicaron que el precipitado estaba conformado por As y S, en una relación entre 0.55 y 0.90 (S:As). El análisis XRD confirmó la presencia de oropimente y rejalgar. Se demostró que, al separar el proceso biológico del proceso de precipitación, afecta la morfología, tamaño de partícula y cristalinidad de los sulfuros de arsénico formados, por lo tanto, se espera que este estudio sea el punto de partida para indagar sobre las condiciones en la precipitación de sulfuros de arsénico, y cómo esto afecta sus propiedades físicas y químicas."; "Arsenic contamination in water represents a high risk to human health and the environment. The WHO establishes 10 ?g/L of arsenic as the maximum permissible limit in water for human use. In Mexico, high concentrations of arsenic are common in aquifers and mining areas such as Matehuala, S.L.P., with levels up to 158 mg/L in water. Existing treatment methods such as filtration and chemical precipitation are expensive and generate toxic by products. Biological remediation, which takes advantage of the metabolic features of arsenic- and sulfate-reducing bacteria, offers a promising alternative for arsenic removal through its biomineralization or formation of arsenic sulfides mineral phases. The objective of the present study was to evaluate the precipitation of arsenic sulfides in a biological physicochemical system for arsenic removal from water. The biological activities (arsenate and sulfate-reducing) of a consortium recovered from contaminated sites were characterized. Afterwards, a fixed bed batch reactor (250 mL working volume) with the two coupled activities was operated at laboratory scale and successfully removed up to 99% of arsenate (2.5 mM) and 100% of sulfate (up to 5 mM) using lactate as electron donor. The biogenic precipitates contained mainly arsenic sulfides (AsS) in fiber-like structures. From the support of the first reactor, two continuous reactors (500 mL each) with separate activities were set up and operated. The arsenate-reducing reactor reached more than 80% of arsenic reduction efficiency, while the sulfate-reducing reactor showed up to 80% sulfate removal efficiency. From the effluents of both reactors, the effect of molar ratios and pH was evaluated in batch experiments at different S:As molar ratios (1.4, 2.7, 5.4) and pH (2, 5 and 6). The results showed a higher arsenic removal efficiency (93%) at pH 2 within one hour and lower removal efficiency (19-64%) at pH 6. Finally, a precipitation reactor was operated at molar ratio S:As 1.5 at pH 2 or 5. At pH 2, arsenic precipitates solubilized after 48 hours, while at pH 5, the precipitates were more stable, achieving up to 92% removal in five days. Finally, SEM-EDS analyses indicated that the precipitate at pH 2 was composed of S and As, in a 1.6 molar ratio (S:As). The precipitate showed spherical morphology with particles between 118 to 280 nm. The X-ray diffraction pattern (XRD) confirmed the presence of crystalline phases of orpiment (As2S3) and realgar (As4S4). Regarding the precipitate at pH 5, SEM micrographs of the precipitate showed a prismatic particle morphology with particle sizes between 1.7 to 3 µm. The EDS results indicated that the precipitate was composed of As and S, in a ratio between 0.55 and 0.90 (S:As). The X-ray diffraction pattern (XRD) confirmed the presence of orpiment and realgar. It was shown that the separation of the biological process from the precipitation process affects the morphology, particle size, and crystallinity of the formed arsenic sulfides. It is therefore expected that this study will be the starting point for investigating the conditions governing the precipitation of arsenic sulfides, which affect their physical and chemical properties." Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/11627/6663 2025-01-01T00:00:00Z http://hdl.handle.net/11627/6657 Ecological relationships between birds and haemosporidian parasites in present and future climate change scenarios Ortega Guzmán, Larissa "Avian haemosporidian parasites, including Plasmodium, Haemoproteus, and Leucocytozoon, are among the most common parasitic infections in wild birds in the Americas. Parasites within each genus exhibit a wide array of environmental tolerance and host specificity, and their distributions are influenced by various environmental factors, the most important being temperature and humidity. Transmitted by dipteran vectors (such as mosquitoes and biting midges), haemosporidian infections can cause significant health issues in wild bird populations, including reduced reproductive success and increased mortality rates. Despite extensive studies on the environmental drivers of distribution and prevalence of these parasites, the potential impacts of climate change on parasite-host dynamics remain difficult to assess due to the complex interactions between the haemosporidians, their hosts, and the environment. In this study, we examined the bioclimatic variables influencing haemosporidian prevalence in avian communities across central to eastern Mexico and continental North America, with a focus on how climate change might affect the distribution trends of haemosporidians in the future. Using spatial modeling, we assessed how the bioclimatic variables, such as temperature and humidity, shape the distribution of haemosporidians across an altitudinal gradient, and in relation to their host specificity. We forecast that in contrasting climate change scenarios, the temperature increases, and precipitation declines might lead to shifts in prevalence trends following the altitudinal gradient, with a potential rise of haemosporidian prevalence at higher elevations, particularly in temperate climates. However, the bioclimatic space associated with haemosporidian prevalence located in arid and semi-arid habitats might become heavily compromised as climate change becomes more severe. In relation to their host specificity, climate change projections suggest a northward latitudinal migration of the bioclimatic variables related to the presence of certain haemosporidian lineages. For specialist lineages, this shift may be more pronounced, given their geographic and host specificity limitations. Under both approaches (altitudinal and latitudinal analysis), our projections suggest that anthropogenic climate change may disrupt the life cycles of both haemosporidians and their vectors, altering infection dynamics and potentially introducing new risks for avian populations. These findings highlight the importance of incorporating climate change projections and analysis into the study of wildlife diseases and underscore the need for further research in relation to the environmental tolerances and host specificity of haemosporidian parasites."; "Los parásitos hemosporidios como Plasmodium, Haemoproteus y Leucocytozoon constituyen algunos de los principales agentes infecciosos en aves silvestres en el continente americano. Los parásitos dentro de cada uno de estos géneros exhiben una amplia gama de tolerancia ambiental y especificidad de hospedero, por lo que sus distribuciones se ven influenciadas por diversos factores medioambientales, de los cuales los más importantes son la temperatura y humedad. Estas infecciones son transmitidas por vectores del orden Diptera (mosquitos y moscas hematófagas) y pueden ocasionar trastornos de salud significativos en las poblaciones de aves silvestres, tales como reducciones en su éxito reproductivo e incrementos en las tasas de mortalidad. No obstante, a pesar de la existencia de diversos estudios acerca de los factores que influyen en la distribución y prevalencia de estos parásitos, aun es difícil evaluar los efectos del cambio climático a largo plazo sobre las dinámicas parásito-hospedero debido a la complejidad de las interacciones entre los hemosporidios, sus hospederos y el medioambiente. En el presente estudio, examinamos las variables bioclimáticas detrás de la prevalencia y presencia de los parásitos hemosporidios en comunidades aviares en el centro-este de México y sobre linajes hemosporidios registrados en América del Norte, con un enfoque especial sobre la manera en que el cambio climático podría afectar las tendencias de distribución de estos parásitos en el futuro. Mediante el uso de modelaje espacial, evaluamos las tendencias de distribución de los hemosporidios a lo largo de un gradiente altitudinal en México y con relación a su especificidad de hospedero bajo una escala continental. Nuestras proyecciones sugieren que, bajo escenarios contrastantes de cambio climático, los incrementos de temperatura y reducción en las tasas de precipitación en el país podrían ocasionar cambios en la expresión de las tasas de prevalencia de los hemosporidios a lo largo de un gradiente altitudinal, con incrementos potenciales de prevalencia en las regiones altas (especialmente en áreas de clima templado). Sin embargo, el espacio bioclimático asociado con la prevalencia de hemosporidios que se encuentra en regiones áridas y semiáridas podría encontrarse fuertemente comprometido conforme el cambio climático se vuelve más severo. Al tomar en consideración los grados de especificidad de hospedero que presentan estos parásitos, las proyecciones de cambio climático sugieren la existencia de una migración latitudinal de las condiciones bioclimáticas relacionadas con la presencia de ciertos linajes hemosporidios hacia el norte del continente, además de una pérdida de espacio bioclimático. Bajo ambos enfoques (análisis altitudinal y latitudinal), nuestras proyecciones sugieren que el cambio climático antropogénico podría alterar las dinámicas de infección y distribución de estos organismos y podría introducir riesgos imprevistos a las poblaciones aviares. Los resultados obtenidos sólo recalcan la importancia de incorporar las proyecciones de cambio climático en el estudio de las enfermedades de vida silvestre y enfatizan la necesidad de realizar mayores investigaciones en relación con la tolerancia ambiental de los parásitos hemosporidios bajo distintos enfoques." This research was funded by the Mexican National Council for Science and Technology (CONACYT) through its “National Problems” research grant program (grant number 2015-01-1628). CONACYT also provided a scholarship for the doctoral studies of Larissa Ortega Guzmán (scholarship number 509157/286185). Tue, 04 Feb 2025 00:00:00 GMT http://hdl.handle.net/11627/6657 2025-02-04T00:00:00Z