This study investigates the use of multi-element compound-specific isotope analysis (ME-CSIA) to monitor degradation processes of methoxychlor, a persistent organochlorine insecticide. Laboratory experiments examined the kinetics, release of transformation products, and carbon and chlorine isotope effects during methoxychlor degradation through alkaline hydrolysis, oxidation with alkaline-activated persulfate, and biotic reductive dechlorination. Results showed that hydrolysis and oxidation did not cause significant carbon and chlorine isotope fractionation, indicating that C-H rather than C-Cl bond cleavage was the rate-determining step. Conversely, biotic reductive dechlorination by a field-derived microcosm under strictly anoxic conditions displayed significant carbon (epsilon C C =-0.9 f 0.3 %o ) and chlorine (epsilon Cl Cl =-1.9 f 1.0 %o ) isotope fractionation. Its corresponding calculated dual isotope slope ( Lambda C/Cl = 0.4 f 0.1) and apparent kinetic isotope effects (AKIEC C = 1.014 f 0.005 and AKIECl Cl = 1.006 f 0.003) indicate a C-Cl bond cleavage as the rate-determining step, highlighting the difference with respect to the other studied degradation mechanisms. Changes in the microbial community diversity revealed that families such as Dojkabacteria, Anaerolineaceae, , Dysgonomonadaceae, , Bacteroidetes vadinHA17, , Pseudomonadaceae, , and Spirochaetaceae, , may be potential agents of methoxychlor reductive dechlorination under anoxic conditions. This study advances the understanding of degradation mechanisms of methoxychlor and improves the ability to track its transformation in contaminated environments, including for the first time an isotopic perspective.

Lake Alboraj, located in southeast Spain, was declared natural Microreserve and included into European Natura-2000 Network due to its contribution to environmental heritage. Unfortunately, the ecological status of the lake has changed dramatically, mainly due to the lowering of water table caused by groundwater abstractions for irrigation. It is a permanent small karstic lake whose surface has reduced in the last decades to nearly the third part of its historical water level. The water column shows a marked seasonal oxycline, that splits an aerobic upper layer (epilimnion) from an anaerobic layer below (hypolimnion). Sequencing 16S rRNA gene amplicons and applying chemical tools at epilimnion, hypolimnion and sediment, showed a clear gradient in the bacterial community structure, which support the co-existence of assimilatory and dissimilatory microbial mediated reactions. Results allows to infer that microbial stratification could provide various physical and chemical environments at different depths in the water column related to biogeochemical reactions providing N-S-C- recycling processes.

Saline lakes are subject to numerous environmental impacts related to human activities, changing the chemical and biological natural conditions of the ecosystem. Sustainable development depends on the conservation of such delicate saline ecosystems, which may hold distinctive biodiversity. Pollution is one of the major threats to surface water bodies, for example by increasing nutrient contents and organic pollutants, including endocrine disrupting chemicals. Microbially mediated redox processes exert a fundamental control on nutrient turnover and contaminant removal. This study examines the influence of land use on the distribution of endocrine disrupting chemicals as well as on the microbial community composition in lacustrine sediments from Pétrola saline Lake (SE Spain). The lake is impacted by anthropogenic activities (agriculture, farming, mining and urban wastewater spills). Applying chemical and molecular tools (sequencing of 16S rRNA gene) showed a clear influence of land use on the chemistry and bacterial abundance of the lake sediments. The sampling points closer to wastewater outflows and mining ponds (2635, 2643 and 2650) showed fewer numbers and types of endocrine disrupting chemicals as well as a smaller number of families in the microbial community. These findings improve our understanding of how land use affects both water chemistry and the abundance of organisms responsible for biogeochemical cycles.

The chemical composition of groundwater and related surface water ecosystems can be modified by intensive agricultural activities. This is the case of the Natural Reserve of Pétrola saline lake (Albacete, SE Spain), which constitutes the discharge area of an unconfined aquifer. The extended use of fertilizers and pesticides poses a threat to ecosystem sustainability. One of the most applied herbicides worldwide has been atrazine. Despite being prohibited in Spain since 2007 by European regulations, atrazine can still be detected due to its high persistence in the environment. Atrazine degradation pathways are mediated by biological processes performed by microorganisms with adapted metabolic mechanisms that make in situ bioremediation possible. To evaluate the presence of such microorganisms in the unconfined aquifer, groundwater was collected from a flowing 37.9 m deep piezometer. DNA was extracted, and the bacterial 16S rRNA gene was amplified and cloned. Later, 93 clones were sequenced, providing the first molecular assessment of bacterial community structure in the deep zones of the aquifer. Some of these bacteria have been previously described to be involved in atrazine degradation. In addition, 14 bacteria were isolated from the groundwater samples and identified by 16S rRNA gene sequencing. DNA from these bacteria was subjected to PCR assays with primers designed for the genes involved in the atrazine degradation pathway. Positive results in the amplification were found in at least three of these bacteria (Arthrobacter sp., Nocardioides sp. and Pseudomonas sp.). The atrazine-degrading genetic potential was shown to be dependent on the trzN and atzA,B,C gene combination. These results suggest for the first time the adaptation of the bacterial population present in deep aquifer zones to atrazine exposure, even after more than 15 years of its ban in Spain. In addition, this study provides the baseline data about the bacterial communities found in deep aquifer zones from the hypersaline lake-aquifer system.

El humedal salino de Pétrola, situado en un ambiente semiárido en el sureste de la provincia de Albacete (España), constituye la zona de descarga de una cuenca endorreica de alrededor de 42 km2. La laguna está sometida a múltiples entradas de contaminación derivadas de actuaciones antrópicas, originando que las condiciones biológicas y físico-químicas de partida de la masa de agua hayan sido gravemente modificadas. La elevada salinidad del sistema (123.000 μS/cm, noviembre 2010) da lugar a un ambiente extremo que propicia condiciones exclusivas capaces de albergar ciertos procesos redox mediados por extremófilos adaptados. Estos microorganismos pueden ejercer un papel fundamental en la atenuación de la contaminación de origen urbano y agrícola existente. Entre las entradas de contaminantes destacan el nitrato, y la atrazina, un herbicida usado ampliamente en las prácticas agrícolas, y sus metabolitos desetilatrazina y deisopropilatrazina. Las concentraciones de atrazina y sus productos de transformación pueden superan los 100 ng/L. Por ello, el objetivo de este trabajo es la búsqueda de microrganismos extremófilos implicados en la atenuación de contaminantes en la laguna de Pétrola, con especial atención en aquellos que puedan estar biodegradar la atrazina. El primer enfoque para la detección de microorganismos extremófilos, que puedan participar en procesos de biorremediación, ha consistido en un análisis metagenómico. Para ello, se recogieron sedimentos de la laguna en 7 puntos cuyas aguas presentan diferentes características físico-químicas. Se extrajo el ADN genómico bacteriano del sedimento y se sometió al análisis metagenómico mediante secuenciación del gen 16S rRNA, lo que permitió caracterizar las poblaciones bacterianas presentes en la laguna. Como resultado, se ha detectado una gran diversidad de microorganismos extremófilos. Entre ellos, destaca el grupo relacionado con procesos de desnitrificación fototrófica y nitrato-sulfato-reducción. Dentro de este grupo, se ha buscado la presencia de microorganismos relacionados con procesos de degradación de contaminantes, aunque, debido al gran número de datos generados, los resultados todavía se encuentran en proceso de análisis. El segundo enfoque ha consistido en la búsqueda de bacterias degradadoras de atrazina, mediante la amplificación por PCR con cebadores diseñados para la amplificación de los genes involucrados en la ruta de degradación de este contaminante organoclorado (Figura). En este punto, se ha conseguido la amplificación de fragmentos, con un patrón diferente en los distintos sedimentos evaluados, lo cual da idea de los diferentes procesos que se están produciendo en puntos de la laguna sometidos a distintas condiciones ambientales. Los resultados ofrecen información acerca de la presencia de microorganismos extremófilos que pueden participar en procesos de atenuación de contaminantes. Se vislumbra la formación de un complejo sistema simbiótico de degradación en cadena que debe seguir estudiándose en mayor profundidad en futuros trabajos orientados a la biorremediación. Espín, Yolanda; Sanz, Guillermo; Valiente, Nicolás; Menchén, Alfonso; Álvarez-Ortí, Manuel; Gómez-Alday, Juan José

Saline lakes are subject to numerous environmental impacts related to human activities. Pollution is one of the major threats to water bodies, since it produces the increase of nitrogen and sulfur contents, changing the chemical and biological conditions of the ecosystem. Microbially mediated redox processes exert a fundamental control on nutrient and contaminant turnover. Therefore, the aim of this study was to determine the influence of land use on the microbial communities responsible for N and S turnover in the lacustrine sediments from Pétrola Lake (SE Spain) disturbed by anthropogenic activities (agriculture, farming, mining, and wastewaters). To reach this goal, chemical and molecular tools (sequencing of 16S rDNA gene) were applied. The results showed the influence of land use on the chemistry and microbial community structure of the sediments from the saline lake. Compared to natural conditions, wastewater and mining showed the largest differences in terms of microbial structure as a result of salinity. These findings provide better understanding of how land use affects the water chemistry and the abundance of organisms responsible for nutrient turnover.