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Biogeochemical processes govern the transport and availability of arsenic in sediments. However, little is known about the transition from indigenous communities to cultivable consortia when exposed to high arsenic concentrations. Such cultivable communities could be exploited for arsenic bioremediation of waste streams and polluted sites. Thus, it is crucial to understand the dynamics and selective pressures that shape the communities during the development of customized bacterial consortia. First, from the arsenic partitioning of two sediments with high arsenic concentrations, we found that up to 55% of arsenic was bioavailable because it was associated with the soluble, carbonate, and ionically exchangeable fractions. Next, we prepared sediment enrichment cultures under arsenate- and sulfate-reducing conditions to precipitate arsenic sulfide biominerals and analyze the communities. The produced biominerals were used as the inoculum to develop bacterial consortia via successive transfers. Tracking of the 16S rRNA gene in the fresh sediments, sediment enrichments, biogenic minerals, and bacterial consortia revealed differences in the bacterial communities. Removing the sediment caused a substantial decrease in diversity and shifts toward the dominance of the Firmicutes phylum to the detriment of Proteobacteria. In agreement with the 16S rRNA gene results, the sequencing of the arrA gene confirmed the presence of phylotypes closely related to Desulfosporosinus sp. Y5 (100% similarity), highlighting the pivotal role of this genus in the removal of soluble arsenic. Here, we demonstrated for the first time that besides being important as arsenic sinks, the biogenic arsenic sulfide minerals are reservoirs of arsenic resistant/respiring bacteria and can be used to culture them.

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El Chichón volcano is one of the most active volcanoes in Mexico. Previous studies have described its poly-extreme conditions and its bacterial composition, although the functional features of the complete microbiome have not been characterized yet. By using metabarcoding analysis, metagenomics, metabolomics and enzymology techniques, the microbiome of the crater lake was characterized in this study. New information is provided on the taxonomic and functional diversity of the representative Archaea phyla, Crenarchaeota and Euryarchaeota, as well as those that are representative of Bacteria, Thermotogales and Aquificae. With culture of microbial consortia and with the genetic information collected from the natural environment sampling, metabolic interactions were identified between prokaryotes, which can withstand multiple extreme conditions. The existence of a close relationship between the biogeochemical cycles of carbon and sulfur in an active volcano has been proposed, while the relationship in the energy metabolism of thermoacidophilic bacteria and archaea in this multi-extreme environment was biochemically revealed for the first time. These findings contribute towards understanding microbial metabolism under extreme conditions, and provide potential knowledge pertaining to "microbial dark matter", which can be applied to biotechnological processes and evolutionary studies.

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The present study aimed to clarify the effect of oxygen respiration on biotransformation of alternative electron acceptors (e.g., nitrate and sulfate) underlying the simultaneous removal of ammonium and sulfate in a single aerated sequencing batch reactor. Complete nitrification was achieved in feast condition, while denitrification was carried out in both feast and famine conditions when aeration intensity (AI) was higher than 0.22 L/(L·min). Reactors R1 [0.56 L/(L·min)], R2 [0.22 L/(L·min)], and R3 [0.08 L/(L·min)] achieved 72.39% sulfate removal efficiency in feast condition, but H2S release occurred in R3. Following exogenous substrate depletion, sulfate concentration increased again and exceeded the influent value in R1, indicating that sulfate transformation was affected by oxygen intrusion. Metagenomic analysis showed that a higher AI promoted sulfate reduction by switching from dissimilatory to assimilatory pathway. Lower AI-acclimated microorganisms (R3) produced H2S and ammonium, while higher AI-acclimated microorganisms (R1) accumulated nitrite, which confirmed that biotransformation of N and S was strongly regulated by redox imbalance driven by aeration. This implied that respiration control, a microbial self-regulation mechanism, was linked to the dynamic imbalance between electron donors and electron acceptors. Aerobic nitrate (sulfate) reduction, as one of the effects of respiration control, could be used as an alternative strategy to compensate for dynamic imbalance, when supported by efficient endogenous metabolism. Moderate aeration induced microorganisms to change their energy conservation and survival strategy through respiration control and inter-genus protection of respiratory activity among keystone taxa (including Azoarcus in R1, Thauera in R2, and Thiobacillus, Ottowia, and Geoalkalibacter in R3) to form an optimal niche in response to oxygen intrusion and achieve benign biotransformation of C, N, and S without toxic intermediate accumulation. This study clarified the biotransformation mechanism of ammonium and sulfate driven by aeration and provided theoretical guidance for optimizing existing aeration-based techniques.

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Sulfate reducing prokaryotes (SRP) are a phylogenetically and physiologically diverse group of microorganisms that use sulfate as an electron acceptor. SRP have long been recognized as key players of the carbon and sulfur cycles, and more recently, they have been identified to play a relevant role as part of syntrophic and symbiotic relations and the human microbiome. Despite their environmental relevance, there is a poor understanding about the prevalence of prophages and CRISPR arrays and how their distribution and dynamic affect the ecological role of SRP. We addressed this question by analyzing the results of a comprehensive survey of prophages and CRISPR in a total of 91 genomes of SRP with several genotypic, phenotypic, and physiological traits, including genome size, cell volume, minimum doubling time, cell wall, and habitat, among others. Our analysis discovered 81 prophages in 51 strains, representing the 56% of the total evaluated strains. Prophages are non-uniformly distributed across the SRP phylogeny, where prophage-rich lineages belonged to Desulfovibrionaceae and Peptococcaceae. Furthermore, our study found 160 CRISPR arrays in 71 SRP, which is more abundant and widely spread than previously expected. Although there is no correlation between presence and abundance of prophages and CRISPR arrays at the strain level, our analysis showed that there is a directly proportional relation between cellular volumes and number of prophages per cell. This result suggests that there is an additional selective pressure for strains with smaller cells to get rid of foreign DNA, such as prophages, but not CRISPR, due to less availability of cellular resources. Analysis of the prophage genes encoding viral structural proteins reported that 44% of SRP prophages are classified as Myoviridae, and comparative analysis showed high level of homology, but not synteny, among prophages belonging to the Family Desulfovibrionaceae. We further recovered viral-like particles and structures that resemble outer membrane vesicles from D. vulgaris str. Hildenborough. The results of this study improved the current understanding of dynamic interactions between prophages and CRISPR with their hosts in both cultured and hitherto-uncultured SRP strains, and how their distribution affects the microbial community dynamics in several sulfidogenic natural and engineered environments.

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PURPOSE: The aim of the present work was to assess the electrogenic activity of bacteria from hydrothermal vent sediments achieved under sulfate reducing (SR) conditions in a microbial fuel cell design with acetate, propionate and butyrate as electron donors. METHODS: Two different mixtures of volatile fatty acids (VFA) were evaluated as the carbon source at two chemical oxygen demand (COD) proportions. The mixtures of VFA used were: acetate, propionate and butyrate COD: 3:0.5:0.5 (stage 1) and acetate - butyrate COD: 3.5:0.5 (stage 2). Periodical analysis of sulfate (SO4 -2), sulfide (HS-) and COD were conducted to assess sulfate reduction (SR) and COD removal along with measurements of voltage and current to assess the global performance of the consortium in the system. RESULTS: Percentage of SR was of 97.5 ± 0.7 and 74.3 ± 1.5% for stage 1 and 2, respectively. The % COD removal was of 91 ± 2.1 and 75.3 ± 9.6 for stage 1 and 2, respectively. Although SR and COD removal were higher at stage 1, in regards of energy, stage 2 presented higher current and power densities and Coulombic efficiency as follows: 741.7 ± 30.5 µA/m2, 376 ± 34.4 µW/m2 and 5 ± 2.7%, whereas for stage 1 these values were: 419 ± 71 µA/m2, 52.7 ± 18 µW/m2 and 0.02%, respectively. A metagenomic analysis - stage 2 - in the anodic chamber, demonstrated that SR was due to Dethiosulfovibrionaceae (HA73), Desulfobacter and Desulfococcus and the electrogenic microorganisms were Planococcus, SHD-231, Proteiniclasticum, vadinCA02, and families Porphyromonadacea and Pseudomonadaceae. CONCLUSIONS: It was demonstrated that microorganisms prevenient from hydrothermal vent sediments adapted to a microbial fuel cell system are able to generate electricity coupled to 74.3 ± 1.5 and 75.3 ± 9.6% of SR and COD removal respectively, with a mixture of acetate - butyrate.

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RESUMEN El Drenaje ácido de mina (DAM) es actualmente el principal contaminante de las regiones mineras. Los reactores bioquímicos pasivos son una tecnología sostenible fácil de instalar que utiliza desechos agroindustriales de la región y puede operar en áreas remotas con poco mantenimiento. Además, son una tecnología limpia que involucra bioprocesos, reacciones químicas y precipitación de metales, minimizando el impacto de los vertimientos ácidos sobre suelos y cuerpos de aguas. Los reactores bioquímicos pasivos son columnas empacadas con una "mezcla reactiva" conformada por materiales orgánicos, inorgánicos y un inóculo microbiano. En esta mezcla se remedia el DAM por medio de procesos fisicoquímicos como la adsorción, precipitación, coprecipitación de los metales y de la reducción del sulfato a sulfuro, mientras se incrementa el pH y la alcalinidad. Con el fin de brindar información reciente, así como las necesidades de investigación en el tema, este documento presenta una revisión de literatura sobre la generación química y biológica de los DAM, así como su remedición utilizando reactores bioquímicos pasivos. El conocimiento de los conceptos básicos de estos procesos es extremadamente útil para evaluar las posibles aplicaciones, beneficios y limitaciones de estos sistemas de tratamiento utilizados por la biotecnología durante la biorremediación de efluentes mineros.

ABSTRACT Acid Mine Drainage (AMD) is currently the main pollutant in mining areas. Passive biochemical reactors are a sustainable technology easy to install using agro-industry waste from the mining region and operating in remote locations. Besides, bioreactors are clean technology that involves bioprocesses, chemical reactions, and metal precipitation, minimizing the impact of AMD on soils and fresh water sources. The passive biochemical reactors are columns packed with a "reactive mixture" consisting of organic, inorganic materials and a microbial inoculum. In this reactive mixture, AMD is remediated through physicochemical processes such as metals adsorption, precipitation, and co-precipitation, as well as, the reduction of sulfate to sulfur, while pH and alkalinity are in-creased. To provide recent information and research needs in the subject, this document presents a review of the literature about the chemical and biological generation of AMD and its remediation using passive biochemical reactors. The knowledge of the basic concepts of these processes is extremely useful to evaluate the possible applications, benefits and limitations of these treatment systems used by biotechnology during the bioremediation of mining effluents.

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Metals are key materials extensively employed in several industries to produce technological and daily-life products. The mining industry that produces such commodities generates Tons of waste that if not remediated can be transferred to the surrounding environment, thus representing a water, air, and soil pollution threat. In this work, we evaluated the feasibility of microbial sulfate reduction (SR) as a management strategy for this waste. Mine tailings were sampled from two abandoned mining sites located in Sonora (northwestern Mexico) and treated in anaerobic microcosms under SR conditions using anaerobic sludge as the inoculum at two different tailing:inoculum ratios (TIR). Major TIR's were found to be the triggering factor for the highest SR activities observed (73.6 ± 8.8 mg SO42- L-1 day-1). This stimulation was linked to the dissolution of sulfate bearing minerals (anglesite, jarosite, and gypsum) which provided additional sulfate for microbial activity. However, under this condition, longer lag phases for SR were observed, which was potentially due to pH inhibition at early incubation stages (pH ~3.7). Despite this, all biologically SR performing treatments presented important sulfide precipitation which was associated to changes in the mineralogy of the mine tailings. Metals of environmental concern such as As, Cd, Co, Cr and, Pb were detected to have shifted from the aqueous extractable phase to the bound to Fe and Mn oxides and residual phases. This finding was in accordance with the non-detectable concentrations of these metals in the aqueous phase by the end of the biological treatment which proved the effectiveness of this approach. This study provides insights into the promising potential of anaerobic microbes for the environmental management of mine tailings.

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A novel Gram-negative, non-spore-forming, vibrio-shaped, anaerobic, alkaliphilic, sulfate-reducing bacterium, designated strain PAR22NT, was isolated from sediment samples collected at an alkaline crater lake in Guanajuato (Mexico). Strain PAR22NT grew at temperatures between 15 and 37 °C (optimum, 32 °C), at pH between pH 8.3 and 10.1 (optimum, pH 9.0-9.6), and in the presence of NaCl up to 10 %. Pyruvate, 2-methylbutyrate and fatty acids (4-18 carbon atoms) were used as electron donors in the presence of sulfate as a terminal electron acceptor and were incompletely oxidized to acetate and CO2. Besides sulfate, both sulfite and elemental sulfur were also used as terminal electron acceptors and were reduced to sulfide. The predominant fatty acids were summed feature 10 (C18 : 1 ω7c and/or C18 : 1 ω9t and/or C18 : 1 ω12t), C18 : 1 ω9c and C16 : 0. The genome size of strain PAR22NT was 3.8 Mb including 3391 predicted genes. The genomic DNA G+C content was 49.0 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that it belongs to the genus Desulfobotulus within the class Deltaproteobacteria. Its closest phylogenetic relatives are Desulfobotulus alkaliphilus (98.4 % similarity) and Desulfobotulus sapovorans (97.9 % similarity). Based on phylogenetic, phenotypic and chemotaxonomic characteristics, we propose that the isolate represents a novel species of the genus Desulfobotulus with the name Desulfobotulus mexicanus sp. nov. The type strain is PAR22NT (=DSM 105758T=JCM 32146T).

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At a "clean air" trade winds site in northeastern Puerto Rico, we found an apparent paradox: atmospheric total mercury (THg) deposition was highest of any site in the USA Mercury Deposition Network, but assimilation into the local food web was quite low. Avian blood THg concentrations (n = 31, from eight species in five foraging guilds) ranged widely from 0.2 to 32 ng g-1 (median of 4.3 ng g-1). Within this population, THg was significantly greater at a low-elevation site near a wetland compared to an upland montane site, even when the comparison was limited to a single species. Overall, however, THg concentrations were approximately an order of magnitude lower than comparable populations in the continental U.S. In surface soil and sediment, potential rates of demethylation were 3 to 9-fold greater than those for Hg(II)-methylation (based on six radiotracer amendment incubations), but rates of change of ambient MeHg pools showed a slight net positive Hg(II)-methylation. Thus, the resolution of the paradox is that MeHg degradation approximately keeps pace with MeHg production in this landscape. Further, any net production of MeHg is subject to frequent flushing by high rainfall on chronically wet soils. The interplay of these microbial processes and hydrology appears to shield the local food web from adverse effects of high atmospheric mercury loading. This scenario may play out in other humid tropical ecosystems as well, but it is difficult to evaluate because coordinated studies of Hg deposition, methylation, and trophic uptake have not been conducted at other tropical sites.

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The extent of fractionation of sulfur isotopes by sulfate-reducing microbes is dictated by genomic and environmental factors. A greater understanding of species-specific fractionations may better inform interpretation of sulfur isotopes preserved in the rock record. To examine whether gene diversity influences net isotopic fractionation in situ, we assessed environmental chemistry, sulfate reduction rates, diversity of putative sulfur-metabolizing organisms by 16S rRNA and dissimilatory sulfite reductase (dsrB) gene amplicon sequencing, and net fractionation of sulfur isotopes along a sediment transect of a hypersaline Arctic spring. In situ sulfate reduction rates yielded minimum cell-specific sulfate reduction rates < 0.3 × 10-15 moles cell-1  day-1 . Neither 16S rRNA nor dsrB diversity indices correlated with relatively constant (38‰-45‰) net isotope fractionation (ε34 Ssulfide-sulfate ). Measured ε34 S values could be reproduced in a mechanistic fractionation model if 1%-2% of the microbial community (10%-60% of Deltaproteobacteria) were engaged in sulfate respiration, indicating heterogeneous respiratory activity within sulfate-reducing populations. This model indicated enzymatic kinetic diversity of Apr was more likely to correlate with sulfur fractionation than DsrB. We propose that, above a threshold Shannon diversity value of 0.8 for dsrB, the influence of the specific composition of the microbial community responsible for generating an isotope signal is overprinted by the control exerted by environmental variables on microbial physiology.

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Trichloroethylene (TCE) is known as a toxic organic compound found as a pollutant in water streams around the world. The ultimate goal of the present work was to determine the TCE concentration that would be feasible to biodegrade on a long-term basis by a sulfidogenic sludge while maintaining sulfate reducing activity (SRA). Microcosms were prepared with sulfidogenic sludge obtained from a stabilized sulfidogenic UASB and amended with different TCE concentrations (100-300 µM) and two different proportions of volatile fatty acids (VFA) acetate, propionate and butyrate at COD of 2.5:1:1 and 1:1:1, respectively to evaluate the tolerance of the sludge. The overall results suggested that the continuous exposure of the microorganisms to TCE leads to inhibition of SRA; nonetheless, the SRA can be recovered after adequate supplementation of carbon sources and sulfate. The most suitable TCE concentration to operate on a long-term basis while preserving SRA was 26-35 mg L-1 (200-260 µM). A low level of expression of the mRNA of the sulfite reductase subunit alpha (dsrA) gene was obtained in the presence of the TCE and its intermediate products. This gene was associated to SRB belonging to the genera Desulfovibrio, Desulfosalsimonas, Desulfotomaculum, Desulfococcus, Desulfatiglans and Desulfomonas.

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Hydrological and hydrochemical processes occurring within riparian zones in temperate mid-latitudes flatland areas have significant implications for water management by controlling nutrient transfer between the watershed and the stream system. The riparian zone in a high-order flatland stream located within a 7063-km2 agricultural watershed in Argentina was investigated to study its hydrological connectivity to upland zones, interactions with the stream, and their implications for groundwater hydrochemistry. The analysis was based on 9-year-long time series of groundwater/stream water levels collected along a 220-m-long transect comprising six piezometers, a river stage sensor, and hydrochemical information from 37 groundwater/stream water sampling campaigns. Samples were analyzed for electrical conductivity (EC), Cl-, SO4+2, (Ca+2 + Mg+2), pH, and redox potential (ORP). Data were interpreted using descriptive statistics, statistical tests, groundwater flux calculations, and identification of hydrological patterns and associated hydrochemical responses. The system was hydrologically controlled by shallow groundwater. Three representative landscape hydrological patterns were identified: disconnected, incipient-weakly connected, and fully connected. Groundwater hydrochemistry was closely linked to hydrological connectivity, which played an important role in the mobilization and fluxes of solutes. Overall, groundwater EC, Cl-, SO4+2, and (Ca+2 + Mg+2) concentrations decreased from upland to lowland. For full connectivity, Cl- concentrations reduced 33%, while SO4+2 reduced 42%, demonstrating the system's buffering capacity. This investigation constitutes the first attempt to formulate the riparian zone functioning in this agricultural region and has contributed to the understanding on the complex interactions between hydrologic regimes of large flatland-high-order streams and shallow groundwater systems in fine-texture sediments.

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Data presented here are related to the original paper "Simultaneous removal of sulfate and arsenic using immobilized non-traditional sulfate reducing bacteria (SRB) mixed culture and alternative low-cost carbon sources" published by same authors (Matos et al., 2018) [1]. The data set here presented aims to facilitate this paper comprehension by giving readers some additional information. Data set includes a brief description of experimental conditions and the results obtained during both batch and semi-continuous reactors experiments. Data confirmed arsenic and sulfate were simultaneously removed under acidic pH by using a biological treatment based on the activity of a non-traditional sulfur reducing bacteria consortium. This microbial consortium was able to utilize glycerol, powdered chicken feathers as carbon donors, and proved to be resistant to arsenite up to 8.0 mg L-1. Data related to sulfate and arsenic removal efficiencies, residual arsenite and sulfate contents, pH and Eh measurements obtained under different experimental conditions were depicted in graphical format. Refers to https://doi.org/10.1016/j.cej.2017.11.035.

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Acid-volatile sulfides (AVS) formation and its role on trace metals bioavailability were studied in semi-arid mangroves. The semi-arid climatic conditions at the studied sites, marked by low rainfall and high evapotranspiration rates, clearly limited the AVS formation (AVS contents varied from 0.10 to 2.34µmolg-1) by favoring oxic conditions (Eh>+350mV). The AVS contents were strongly correlated with reactive iron and organic carbon (r=0.84; r=0.83 respectively), evidencing their dominant role for AVS formation under semi-arid conditions. On the other hand, the recorded ΣSEM/AVS values remained >1 evidencing a little control of AVS over the bioavailability of trace metals and, thus, its minor role as a sink for toxic metals.

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Methanogenesis and sulfate reduction are important microbial processes in hypersaline environments. However, key aspects determining substrate competition between these microbial processes have not been well documented. We evaluated competitive and non-competitive substrates for stimulation of both processes through microcosm experiments of hypersaline microbial mat samples from Guerrero Negro, Baja California Sur, Mexico, and we assessed the effect of these substrates on the microbial community composition. Methylotrophic methanogenesis evidenced by sequences belonging to methanogens of the family Methanosarcinaceae was found as the dominant methanogenic pathway in the studied hypersaline microbial mat. Nevertheless, our results showed that incubations supplemented with acetate and lactate, performed in absence of sulfate, also produced methane after 40 days of incubation, apparently driven by hydrogenotrophic methanogens affiliated to the family Methanomicrobiaceae. Sulfate reduction was mainly stimulated by addition of acetate and lactate; however, after 40 days of incubation, an increase of the H2S concentrations in microcosms amended with trimethylamine and methanol was also observed, suggesting that these substrates are putatively used for sulfate reduction. Moreover, 16S rRNA gene sequencing analysis showed remarkable differences in the microbial community composition among experimental treatments. In the analyzed sample amended with acetate, sulfate-reducing bacteria (SRB) belonging to the family Desulfobacteraceae were dominant, while members of Desulfohalobiaceae, Desulfomicrobiaceae, and Desulfovibrionaceae were found in the incubation with lactate. Additionally, we detected an unexpected high abundance of unclassified Hydrogenedentes (near 25%) in almost all the experimental treatments. This study contributes to better understand methanogenic and sulfate-reducing activities, which play an important role in the functioning of hypersaline environments.

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Novel Gram-stain-negative, non-spore-forming, vibrio-shaped, anaerobic, alkaliphilic, sulfate-reducing bacteria, designated strains PAR180T and PAR190, were isolated from sediments collected at an alkaline crater lake in Guanajuato (Mexico). Strain PAR180T grew at temperatures between 15 and 40 °C (optimum 35 °C), and at pH between 8.3 and 10.4 (optimum 9). It was halotolerant, growing with up to 8 % (w/v) NaCl. Lactate, formate, pyruvate and ethanol were used as electron donors in the presence of sulfate and were incompletely oxidized to acetate and CO2. The isolate was able to grow with hydrogen and with CO2 as a carbon source. Beside sulfate, sulfite and thiosulfate were used as terminal electron acceptors. The isolate was able to grow by disproportionation of sulfite and thiosulfate, but not elemental sulfur, using acetate as a carbon source. The predominant fatty acids were C16 : 0, C16 : 1ω7c and summed feature 10 (C18 : 1ω7c and/or C18 : 1ω9t and/or C18 : 1ω12t). The DNA G+C content was 56.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that it belongs to the genus Desulfonatronum, class Deltaproteobacteria. Its closest relative is Desulfonatronum thiosulfatophilum (98.7 % 16S rRNA gene sequence similarity). The DNA-DNA relatedness value between strain PAR180T and the type strain of D. thiosulfatophilum was 37.1±2.5 %. On the basis of phylogenetic, phenotypic and chemotaxonomic characteristics, the isolates is considered to represent a novel species of the genus Desulfonatronum, for which the name Desulfonatronum parangueonense sp. nov. is proposed. The type strain is PAR180T (=DSM 103602T=JCM 31598T).

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Resumen Los drenajes ácidos de mina (DAM) son vertimientos con bajo pH, alta concentración de metales y sulfato. Son considerados el mayor problema ambiental de la industria minera y prevenir su formación es la mejor alternativa ambiental y económica. En este estudio, se evaluó el compost de champiñón como enmienda de carbono orgánico para prevenir la formación de DAM. Se construyeron tres celdas en tubos de PVC (2,4 L), llenas con 300 g de mezcla de compost de champiñón y estéril de carbón en diferentes proporciones (40:60, 25:70, 60:40) y 400 mL de agua (18,5Ω). Los cambios químicos en el lixiviado, así como la actividad microbiana en las mezclas fueron monitoreados durante 6 semanas. En los lixiviados el oxígeno disuelto (< 2,0 mg L-1) y potencial de óxido reducción (< (100 mV) disminuyeron, mientras el pH (> 6,5) y la alcalinidad (> 1.500 mg CaCO3 L-1) incrementaron. Además, todas las mezclas fueron eficientes en precipitar los metales (Fe2+ > 95%; Mn2+ > 96%; Zn2+ > 52%) y remover sulfato (> 50%). Sin embargo, en la celda que contenía una proporción de compost y estéril de 25:75 se observó una producción significativa de sulfuro y una mayor actividad microbiana, indicando la presencia de bacterias sulfato-reductoras. Los resultados muestran que el compost de champiñón puede ser utilizado como enmienda orgánica de carbón para contrarrestar la formación de DAM y que la mezcla 25:75 puede ser una opción promisoria para usar en campo en el Distrito minero de Zipaquirá (Colombia).

Abstract The Acid mine drainage (AMD) are discharges characterized by low pH and high concentrations of sulfate and metals. AMD is considered as a serious problem of the mining industry and preventing its formation is the best environmental and economical option. Mushroom compost was evaluated as organic carbon amendment to promote sulfate reduction and metal sulfide precipitation during AMD formation. Three PVC cells (2.4 L) were filled with 300 g of the mixture of mushroom compost and coal mining waste in different proportions (40:60, 25:70, 60:40 %) and 400 mL of water (18,5 Ω). The chemical change in the leachates and the microbial activity in the mixtures were evaluated for 6 weeks. In leachates, dissolved oxygen (< 2,0 mg L-1) and redox potential (< (100 mV) decreased while pH (> 6,5) and alkalinity (> 1500 mg CaCO3 L-1) increased. Besides, all mixtures were efficient for metals precipitation (Fe2+ > 95%; Mn2+ > 96%; Zn2+ > 52%) and sulfate reduction (> 50%). However, a significant production of sulfide and a greater microbial activity was observed in the mixture of mushroom compost and coal mining waste 25:75, indicating the presence of sulfate-reducing bacteria. The results showed that mushroom compost could be used as organic carbon amendment to prevent AMD generation and that the mixture 25:75 could be a promising option to be used in Zipaquirá Mining District (Colombia).

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Marine microorganisms that are obtained from hydrothermal vent sediments present a great metabolic potential for applications in environmental biotechnology. However, the work done regarding their applications in engineered systems is still scarce. Hence, in this work, the sulfate reduction process carried out by a marine microbial community in an upflow anaerobic sludge blanket (UASB) reactor was investigated for 190 days under sequential batch mode. The effects of 1000 to 5500 mg L-1 of SO4-2 and the chemical oxygen demand (COD)/SO4-2 ratio were studied along with a kinetic characterization with lactate as the electron donor. Also, the feasibility of using the sulfide produced in the UASB for copper precipitation in a second column was studied under continuous mode. The system presented here is an alternative to sulfidogenesis, particularly when it is necessary to avoid toxicity to sulfide and competition with methanogens. The bioreactor performed better with relatively low concentrations of sulfate (up to 1100 mg L-1) and COD/SO4-2 ratios between 1.4 and 3.6. Under the continuous regime, the biogenic sulfide was sufficient to precipitate copper at a removal rate of 234 mg L-1 day-1. Finally, the identification of the microorganisms in the sludge was carried out; some genera of microorganisms identified were Desulfitobacterium and Clostridium.

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The aim of the present study was to assess the bioremediation of estuarine sediments contaminated with diesel oil. The following two experiments were performed: natural attenuation (NA) and stimulated natural attenuation (SNA), using rhamnolipid as biosurfactant. Sediment samples were accommodated into glass columns and then contaminated with diesel oil on the top. The column profiles were separated into surface, middle, and bottom for the analyses. The 16 polycyclic aromatic hydrocarbons (PAHs) prioritized by US Environmental Protection Agency (EPA) were monitored for 349 days. Those with three and four rings showed increasing concentrations through the operation period in the middle and bottom samples, particularly between days 111 and 338, and in the SNA experiment. Those with five and six rings were also detected in the deeper portions of the columns, suggesting the percolation of PAHs with a high molecular weight. Total organic carbon was reduced by 91 and 89 % in the NA and SNA samples, respectively, although no statistically significant differences (p > 0.05) were found between the two treatments. The analyses by denaturing gradient gel electrophoresis indicated a slight shift in the microbial community structure over the experiments. Microorganisms belonging to the γ-Proteobacteria phylum were the main bacteria involved. The archaeal community exhibited dominance of hydrogenotrophic methanogens, indicating the obligate anaerobic biodegradation of intermediate compounds from hydrocarbon degradation.

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Graphene oxide (GO) is reported for the first time as electron shuttle to increase the redox conversion of the azo compound, reactive red 2 (RR2, 0.5mM), and the nitroaromatic, 3-chloronitrobenzene (3CNB, 0.5mM). GO (5mgL(-1)) increased 10-fold and 7.6-fold the reduction rate of RR2 and 3CNB, respectively, in abiotic incubations with sulfide (2.6mM) as electron donor. GO also increased by 2-fold and 3.6-fold, the microbial reduction rate of RR2 by anaerobic sludge under methanogenic and sulfate-reducing conditions, respectively. Deep characterization of GO showed that it has a proper size distribution (predominantly between 450 and 700nm) and redox potential (+50.8mV) to promote the reduction of RR2 and 3CNB. Further analysis revealed that biogenic sulfide plays a major role on the GO-mediated reduction of RR2. GO is proposed as an electron shuttle to accelerate the redox conversion of recalcitrant pollutants, such as nitro-benzenes and azo dyes.

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