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Minerals have been important throughout history, but nowadays, their use has increased, as well as their extraction needs. Therefore, due to the growing demand for metals, and both the depletion of high-grade ores and their related environmental concerns, the mining industry has been forced to leave behind the past traditional techniques of metal recovery (use of inorganic acids), and adopt eco-friendlier alternatives, such as the utilization of weaker leaching agents, such as organic acids. Thus, the present review is focused on the use of microbially-produced organic acids as a promising alternative to conventional techniques in the mining industry, with emphasis on the following topics: a) the advantages and disadvantages of the use of organic acids for leaching purposes, b) the main microorganisms studied for the production of these organic acids, c) a summary of the latest reports on bioleaching as well as a comparison of the existent techniques; d) the explanation of leaching mechanisms where organic acids may be involved, to fulfill metal recovery; and, e) interactions between metallic ions and organic acids. The review of the current knowledge regarding the use of organic acids for leaching purposes seeks the visualization of relevant strategies that may be improved for metal-recovery processes, intending to develop circular economy practices that may have the potential to be implemented at an industrial scale.

Acidithiobacillus thiooxidans has been used in bioleaching processes, being recognized for its high metal leaching ability from industrial wastes. In the present work, the sulfur-oxidizing activity of A. thiooxidans DSM 26636, adapted to increasing concentrations of ore was assessed, finding that at 28 days with 3% (w/v) of ore sample, the culture produces high amounts of the sulfate ion (SO4−2) and sulfuric acid (H2SO4) and causes a decrease in the pH value, compared to the negative control. Also, there was observed a net removal of As, Zn, Fe, Al, Cu, and Au in concentrations of 48.23 ± 3.11, 264.02 ± 26.27, 9055.81 ± 210.39, 605.29 ± 30.26, 2158 ± 359.04, and 0.99 ± 0.37 mg/kg, respectively. Thus, the present work shows the potential of A. thiooxidans DSM 26636 to be used for the extraction of metals contained in ores, especially for those containing Cu, Zn, As, Fe, and Al.

There is currently controversy over the use of quantum dots (QDs) in biological applications due to their toxic effects. Therefore, the purpose of the present study was to evaluate the toxic effect of chemical and biogenic (synthesized by

The present study evaluates the ability of Acidithioobacillus thiooxidans DSM 26636 to grow and leach metals from industrial wastes (IW) containing different metal compositions, coded as IW-steel and IW-scrap. For this purpose, biolixiviation processes were assessed during 21 days at 30°C and 150 rpm, with 1% (w/v) of IW pulp density. Microbial growth was evaluated periodically by measuring sulfates´ production; pH and sulfuric acid concentration were also monitored, and metal bioleaching was evaluated by ICP-OES. Results showed that A. thiooxidans sulfur-oxidizing activity was higher in the presence of IW-steel. Specifically, sulfates and sulfuric acid production in IW-steel corresponded to 21,524 mg/L and 0.096 M, respectively, with a pH diminution to 1.54. In the case of IW-scrap, sulfates´ production only increased to up to 4392 mg/L at day 21, and not so significant changes were observed in pH and sulfuric acid concentration. Besides, metal removal was higher in IW-steel, being Fe > Mn > Mg ≥ Zn ≥ Cu > Cr ≥ Ni. The results obtained reinforce the fact that A. thiooxidans DSM 26636 presents an elevated potential to be employed in biotreatment processes, and that its biolixiviation efficiency strongly depends on the metal content present in the residues.

Plastics are widely used for various applications. Once discarded, it is commonly known that they represent a high environmental threat due to their slow degradation; for this reason, there is an imminent need to replace these products with eco-friendlier ones. In the present work, four bacterial polyhydroxybutyrate (PHB) producers, two consortia, and two isolated strains were successfully recovered from the facilities of a paper-manufacturing industry. Spectroscopic studies of the biopolymers obtained from these bacteria corroborated their PHB production capabilities, ranging from 4.04 ± 0.16 to 23.82 ± 3.39 g/L. The characterization of the isolate that presented the highest production yield initially coded as E22 led to the identification of a Klebsiella pneumoniae strain, which, compared with other PHA bacterial producers reported to date, could be considered with high production potential. The strain E22 was grown in 5 different media prepared from fruit peel residues of banana, orange, papaya, watermelon, and melon, to determine its growth and PHA production capabilities in these low-cost media. The results obtained show different bacterial growth yields among the media tested, although PHB production yields and productivities were similar in all these low-cost media. Cellular accumulation of the biopolymer was higher in watermelon peel medium (8.4 × 10−10 g/CFU). These results reveal the potential of K. pneumoniae E22 for PHB production applications and establish encouraging alternatives to be broader explored regarding low-cost media that could enhance the scale-up of bacterial PHA production processes.

The potential of Acidithiobacillus (Thiobacillus) genus members, namely Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, for bioleaching purposes is known. Specifically, previous studies have shown the potential of A. thiooxidans strain DSM 26636 used in bioleaching processes to remove metals in high-metal-content matrices. All Acidithiobacillus growth-monitoring techniques available to date, including sulfate production, commonly used, present disadvantages. Thus, the current work shows a technique based on DNA quantification to evaluate the growth of A. thiooxidans DSM 26636, which is useful even in the presence of a high-metal-content residue. This proposed methodology may represent a functional complementary tool to evaluate Acidithiobacillus growth to develop biometallurgical applications.

La habilidad de cuatro filtrados extracelulares (FE) obtenidos de la biomasa de A. alternata al ser crecida en cuatro medios de cultivo diferentes, nombrados Caldo Malta Dextrosa (CMD), Caldo Papa Dextrosa (CPD), Sacarosa (S) y Czapek (C), fueron evaluados para biosintetizar nanoparticulas de hierro (FeNPs). Para evidenciar la biosintesis de nanoparticulas se realizo un barrido en el espectro de absorcion UV-Vis de 200 a 600 nm a todas las muestras, y analizadas por microscopia electronica de transmision (TEM). La forma y tamano de las FeNPs sintetizadas fue estudiada usando el software SPIP 6.2.0. De los cuatro filtrados extracelulares empleados, la biosintesis de las nanoparticulas fue posible solo en los FE-CPD y FE-C, evidenciando su presencia en el espectro UV-vis al formar una banda de absorcion a los 226 y 225 nm respectivamente, y una meseta alrededor de los 270 nm para el FE-CPD, y 290 nm para el FE-C. Las nanoparticulas sintetizadas presentaron forma esferica y polidispersas, las sintetizadas con el FE-CPD presentaron tamanos de 20-40 nm, mientras que las sintetizadas con el FE-C tuvieron tamanos de 10-80 nm. Despues de seis meses de produccion, las nanoparticulas obtenidas con el FE-C se analizaron por microscopia mostrando un aumento de tamano de hasta 5 µm aproximadamente, posiblemente debido a la atraccion magnetica de estos materiales. Para el FE-S un pico de 231 nm fue observado pero las imagenes TEM mostraron la formacion de microcristales de hierro, y cristales de hierro para el FE-CMD cuya intensidad maxima de absorcion estuvo entre los 225 a 303 nm. El medio de cultivo empleado para producir la biomasa del hongo y obtener el FE tiene una influencia en la biosintesis de nanoparticulas de hierro, aun en el caso del mismo microorganismo. Las FeNPs biosintetizadas por A. alternata podrian ser empleadas en la remocion de contaminantes o como agentes microbi

La seguridad microbiologica de alimentos es un tema importante, el genero Aspergillus es de gran interes dada la frecuencia de contaminacion de los granos por sus toxinas. El presente estudio describe el uso de un plasma frio generado a partir de argon y de una mezcla de argon nitrogeno como metodo de sanitizacion de granos de lenteja. Para el estudio, cada grano fue previamente sanitizado y expuesto a conidios de Aspergillus flavus, cuatro diferentes ensayos fueron realizados, usando unicamente argon y una mezcla de los gases argon-nitrogeno para generar el plasma, a una velocidad de flujo de nitrogeno de 1.2, 0.81 y 0.32 L/min. Cada grano fue expuesto durante 5, 10 y 15 min al plasma, cada ensayo fue realizado por triplicado. Como controles, se emplearon granos no expuestos al plasma. Todos los tratamientos con plasma mostraron un efecto letal sobre la viabilidad de los conidios de A. flavus en periodos que van de 5 a 15 min. La aplicacion del plasma generado por argon mostro una reduccion logaritmica de 0.81 (84 %) al final de los 15 min de exposicion. El plasma generado con la mezcla de gases argon-nitrogeno a 0.81 y 0.32 L/min presento un efecto letal mayor en comparacion con el plasma generado con argon. Aunque no se logro la esterilizacion completa de las lentejas, se observo una reduccion logaritmica de 1.43 (96.44 %) y 5.53 (99.99 %) de los conidios de A. flavus despues de 15 min al ser expuestos al plasma generado por la mezcla argon-nitrogeno a velocidades de flujo de nitrogeno de 0.81 y 0.32 L/min respectivamente. La velocidad de flujo de 0.32 L/min mostro una reduccion de mas de 3 unidades logaritmicas, por lo que este tratamiento tuvo un efecto fungicida. La menor reduccion logaritmica de 0.3 (50.3 %) fue observada a una velocidad de flujo de nitrogeno de 1.2 L/min. Adicionalmente, como consecuencia de la exposicion al plasma, los conidios d

The aim of the present study was to isolate microorganisms able to tolerate Ni2+ and V5+ from different sites located close to a mineral mine in Guanajuato, Mexico, and then to evaluate the...

Nanotechnology has become a research area with promising results for technological innovation. Endodontics can benefit from this field of research by increasing the success rate of the treatment, which currently ranges between 86% and 98% and has varied very little over the years. One of the causes of endodontic treatment failure is based on the presence of Enterococcus faecalis. The objective of this investigation is to evaluate the antibacterial effect of a gel preparation containing silver nanoparticles (Ag-NP) against E. faecalis present in the walls of the root canal. 60 extracted human uniradicular teeth that were instrumented with Wave One Gold (Denstplay/USA) and subsequently contaminated with Enterococcus faecalis. For antibacterial evaluation, intra-canal conducting was placed, and several groups were formed: a) Ag-NP 300 ug/MI gel; b) Ag-NP 500 ug/MI gel; c) Ca (OH) 2 (Ultracal from Ultradent/USA) and the control group. They were incubated at 37°C and a sample was taken every 24 h for 7 days. The Ag-NP gel showed antimicrobial activity against E. faecalis with a value of minimum inhibitory concentration and minimum bactericidal concentration of 300 g/ml and 900 g/ml, respectively. When the Ag-NP gel was used as an intra-canal conducting drug in an in-vitro model, its antimicrobial effect at 300 g/ml and 500 g/ml was equivalent to the action of Ca(OH)2.

Spent catalysts represent an environmental concern, mainly due to their elevated metal content. Although conventional treatment methods for spent catalysts are available, they generate large volumes of potentially harmful wastes and gaseous emissions. To overcome the environmental impact, biotechnological approaches are currently being explored and developed. Thus, the current study assayed the capability of Bacillus megaterium strain MNSH1-9K-1 to remove Al, Ni, V and Ti contained in the spent catalyst coded as ECAT-TL-II. To this end, B. megaterium MNSH1-9K-1 growth and metal uptake abilities in the presence of ECAT-TL-II spent catalyst at 15% (wt/vol) pulp density were evaluated in modified Starkey medium at 37 °C and 200 rpm. The results presented here show B. megaterium resistance capability to the high-metal content residue, and its Al, V and Ni removal ability, in 1,059.15 ± 197.28 mg kg-1 of Al, 43.39 ± 24.13 mg kg-1 of V and 0.58 ± 0.00 mg kg-1 of Ni, corresponding to the 0.79%, 1.63% and 0.46% of each metal content, respectively, while no Ti removal was detected. Besides, it was observed that the sporulation process took place in B. megaterium cells in the presence of the spent catalyst. The results shown in this study suggest the potential of the strain MNSH1-9K-1 for the removal of metals contained in high-metal content residues, contributing also to the knowledge of the metal resistance and removal abilities of B. megaterium in the presence of a spent catalyst, and how morphological cell changes may be occurring while metal removal is taking place.

Previous work has demonstrated that Bacillus megaterium, besides showing an elevated resistance to heavy metals, possesses the ability to remove metals like Ni, Hg, and V from liquid media.

Los altos niveles de toxicidad generados por el alto contenido de metales en los residuos industriales han generado problemas ambientales y de salud. Una de las estrategias para reducir la carga metalica en estos residuos podria ser mediante el uso de bacterias sulfooxidantes debido a que tienen la habilidad de oxidar azufre y producir acido sulfurico, el cual esta implicado en la lixiviacion de metales. Asi, el objetivo de la presente investigacion fue evaluar el crecimiento de Acidithioobacillus thiooxidans DSM26636 y su habilidad de lixiviar metales de escorias y cenizas de una planta de combustion de carbon. El crecimiento microbiano fue monitoreado mediante la produccion de sulfatos y acido sulfurico. El contenido de metales en las escorias y cenizas se determino mediante ICPOES. Los experimentos se llevaron a cabo durante 21 dias a 30°C y 150 rpm en matraces Erlenmeyer de 125 mL conteniendo 30 mL de medio Starkey modificado adicionado con azufre elemental al 1%, las cenizas y/o escorias fueron adicionadas al 1%. Los resultados mostraron que Acidithioobacillus thiooxidans fue capaz de lixiviar V, Fe, Mg, Al, Si y Ni de las escorias. En cuanto a las cenizas, los metales lixiviados fueron Al, Ni, Sn, Mg, Zn y Si. En resumen, Acidithioobacillus thiooxidans puede ser utilizada para la lixiviacion de metales contenidos en residuos de escorias y cenizas provenientes de una planta de combustion de carbon

Spent catalysts are classified as hazardous residues of major environmental concern, mainly due to its elevated metal content. Although conventional spent catalysts treatment methods are available, they generate harmful wastes. Thus, biotechnological approaches are currently being explored to overcome the negative impacts generated by traditional treatment technologies. The present work studied the ability of Cupriavidus metallidurans CH34 to remove heavy metals contained in a spent catalyst that came from an oil refining process. To this end, C. metallidurans resistance to a spent catalyst at 1% (w/w) of pulp density was evaluated, as well as its ability for the removal of the metals contained therein. The results showed that the strain was able to remove 931.56 ± 95.38 mg/kg, and 2111 ± 251.81 of Mo and V, respectively. Considering the elevated toxic nature of spent catalysts, is imminent to develop alternative methods to treat this kind of residues in order to diminish their high metal content. Hence, the data presented here exhibit the first insights into C. metallidurans ability for Mo and V removal from a spent catalyst, and explores for the first time C. metallidurans potential to be used on spent catalysts biotreatment processes.

El estudio evaluo la habilidad de lixiviacion d el medio extracelular producido por un hongo, el cual fue identificado como Alternaria alternata . El estudio comprendio la seleccion de un medio de cultivo que favor ece la produccion de acidos organicos y de sideroforos , los medios de cultivo evaluados fueron m edio de sacarosa y Czapek. Una vez seleccionado el medio de cultivo, se continuo con el estudio de biolixiviacion de metales de un catalizador al 1 y 5%, utilizando el medio extracelular en medio de sacarosa e incubando a 30°C, 150 rpm durante 7 dias. Los resultados indicaron que el medio extracelular disminuyo su pH de 6 a 4.8 ; en este medio se producen sideroforos . E l estudio de lixiviacion de metales en presencia del catalizador demostro que el extracto del hongo es capaz de lixiviar metales ; la concentracion del catalizador tiene un efecto importante sobre la remocion de los metales y sobre la especificidad hacia los met ales; a una concentracion de catalizador del 1%, se removieron los siguientes metales, en orden descendente, V > Al > Si > Mo > Mg > Fe > Ni > As > Cr despues de 48 h. Este es el primer reporte sobre la remocion de metales a partir de un catalizad or por el medio extracelular de A . alternata lo cual abre nueva s alternativas de investigacion para el tratamiento de residuos peligrosos con alto contenido metalico

El incremento en la contaminacion de agua por metales pesados es considerada una situacion alarmante a nivel mundial, debido al impacto adverso que estos generan en los ecosistemas y en la salud humana. Las tecnicas convencionales para disminuir la carga d e metales presentan desventajas, como son: la incompleta remocion de los metales, la produccion de lodos toxicos y los altos costos de operacion. En contraste, los enfoques biotecnologicos representan una alternativa, ya que se consideran mas amigables con el ambiente, tienen costos de operacion menores y la eficiencia de remocion de metales es mayor cuando estos se presentan en bajas concentraciones. Anteriormente se ha demostrado que la presencia simultanea de mas de un metal puede generar efectos sinergi cos, aditivos o antagonicos, afectando asi su remocion, y tambien ha sido reportada la habilidad de B. megaterium MNSH1 - 9K - 1 para remover metales . Por ello, el objetivo del presente trabajo fue analizar las propiedades de resistencia y remocion de Ni de la cepa MNSH1 - 9K - 1 en medio liquido, asi como evaluar la variacion de dichas propiedades en presencia de Al, tambien considerado como un metal toxico comunmente encontrado en los residuos industriales . Para ello, B. megaterium fue crecida en medio LB con la adicion de Ni y/o Al en diversas concentraciones, analizandose tanto la resistencia como la capacidad de remocion de Ni, por medio de cuenta viable y Espectrometria de Emision Optica por Plasma Acoplado Inductivamentente (ICP - OES), de forma respectiva. Los resultados obtenidos sugieren fuertemente que B. megaterium MNSH1 - 9K - 1 presenta una mayor susceptibilidad a Ni que a Al, y que la remocion de Ni es promovida por la presencia de Al

After hydrodesulfurization of Mexican oil's sour acid gases, a sulfur toxic waste is recovered, we used it to synthesize cadmium sulfide quantum dots, which have been recently studied due to their optical (high photostability, high quantum yield and fluorescence) and catalytic properties. Increased demand of cadmium sulfide quantum dots has led to research of new synthesis methods that with higher yields, increased control over particle diameter, that produce hydrophilic quantum dots -as most of them are obtained in organic solvents- and that are environmentally friendly because most methods employ toxic materials or involve a high energy consumption. This study attempted to synthesize hydrophilic cadmium sulfide quantum dots using an environmentally friendly method with a fungus capable of transforming a dangerous waste into a high-value-added product. Mycelia of Fusarium oxysporum f. sp. lycopersici were incubated with 1 mM cadmium nitrate and 1% (w/v) sulfur waste at 30 °C for 24 h, then the biomass was separated through paper filtration. The filtrate became yellow indicating presence of extracellular cadmium sulfide quantum dots, as was confirmed by increased UV–vis absorption around 300 nm and fluorescence at 510 nm. The biomass of Fusarium oxysporum f. sp. lycopersici produced after 24 h, extracellular stable, hydrophilic and biocompatible cadmium sulfide quantum dots from a sulfur dangerous waste. Biosynthesized quantum dots were circular with diameter of 6.116±2.111 nm and had a wurtzite crystalline structure.

Bacillus megaterium strain MNSH1-9K-1, isolated from a high-metal content site in Guanajuato, Mexico, has the intrinsic capacity to remove vanadium (V) and nickel (Ni) from a petrochemical spent catalyst, and counteract the toxic effects produced in the cell due to the presence of oxidative stress. Since knowledge of the molecular components involved in the microbial resistance to spent catalysts is scarce, this study aimed to identify the proteins potentially involved in the enhanced resistance of a B. megaterium strain, during the removal of metals contained in a spent catalyst. Thus, the current research uses a proteomic approach to investigate and evidence the differences in the molecular resistance mechanisms of two B. megaterium strains, one isolated from a mining site and a wild type strain, when both are exposed to a spent catalyst. In addition, we studied their ability to eliminate nickel (Ni), vanadium (V), aluminum (Al) and molybdenum (Mo). The data presented here may contribute to the knowledge of the molecular mechanisms involved in the resistance of B. megaterium to high metal content wastes, as well as its potential utilization for the recovery of valuable industrial metals.

Metals are among the most prevalent pollutants released into the environment. For these reasons, the use of biomarkers for environmental monitoring of individuals and populations exposed to metal pollution has gained considerable attention, offering fast and sensitive detection of chemical stress in organisms. There are different metal resistance genes in bacteria that can be used as biomarkers, including cation diffusion facilitators carrying metal ions; the prototype is the cobalt-zinc-cadmium transporter (czcD). The present study reports the expression changes in the czcD gene in Bacillus megaterium and Microbacterium liquefaciens under nickel and vanadium exposure by real-time polymerase chain reaction. The nickel-vanadium-resistant strains of B. megaterium and M. liquefaciens used in this study were isolated from mine tailings in Guanajuato, Mexico. The czcD gene showed high expression under exposure to 200 ppm of Ni and 200 ppm of V during the logarithmic growth phase of M. liquefaciens in PHGII liquid media. In contrast, no changes were observed in B. megaterium during logarithmic and stationary growth, perhaps due to the gene having differential expression during the growth phases. The expression profiles obtained for czcD show the possibility of using this gene from M. liquefaciens as a biomarker of nickel and vanadium pollution in microorganisms.

The aim of the present study was to isolate microorganisms able to tolerate Ni

This study describes extracellular biosynthesis of cadmium sulfide quantum dots by Fusarium oxysporum f. sp. lycopersici. Mycelia was incubated with a cadmium sulfate solution at 30°C and after 12 days the mixture became yellow, then the biomass was discarded through paper filtration. The filtrate containing extracellular cadmium sulfide quantum dots displayed increased UV-Vis absorption from 300 - 500 nm and fluorescence at 520 nm which was not shown when incubated without cadmium sulfide, thus indicating the presence of biologically synthesized quantum dots. Transmission electron microscope analysis of biologically synthesized quantum dots evinced individual 2 - 6 nm diameter circular nanoparticles of uniform size. Energy dispersive spectroscopy confirmed the presence of S and Cd. Additionally, this study showed the relevance in the use of positive and negative controls when evaluating the biosynthesis of CdS quantum dots using UV-Vis and fluorescence spectrophotometry.

Bacillus megaterium MNSH1-9K-1 and Microbacterium liquefaciens MNSH2-PHGII-2, 2 nickel- and vanadium-resistant bacteria from mine tailings located in Guanajuato, Mexico, are shown to have the ability to remove 33.1% and 17.8% of Ni, respectively, and 50.8% and 14.0% of V, respectively, from spent petrochemical catalysts containing 428 ± 30 mg·kg−1Ni and 2165 ± 77 mg·kg−1V. In these strains, several Ni resistance determinants were detected by conventional PCR. The nccA (nickel–cobalt–cadmium resistance) was found for the first time in B. megaterium. In M. liquefaciens, the above gene as well as the czcD gene (cobalt–zinc–cadmium resistance) and a high-affinity nickel transporter were detected for the first time. This study characterizes the resistance of M. liquefaciens and B. megaterium to Ni through the expression of genes conferring metal resistance.

Spent catalysts are considered as hazardous residues of major concern, mainly due to the simultaneous presence of several metals in elevated concentrations. Although hydrometallurgical, pyrometallurgical and chelating agent methods are available to remove and recover some metals contained in spent catalysts; these procedures generate potentially hazardous wastes and the emission of harmful gases. Thus, biotechnological treatments are currently gaining importance to avoid the negative impacts of chemical technologies. To this end, diverse microorganisms have been used to assess the removal of metals from spent catalysts, comprising bacteria, archaea and fungi, whose resistance and metal uptake capabilities differ depending on the microorganism tested. Acidophilic sulfur oxidizing bacteria have been used to investigate the biotreatment and extraction of valuable metals from spent catalysts, namely Acidithiobacillus thiooxidans and Acidithiobacillus ferroxidans, as they present the ability to produce leaching agents such as sulfuric acid and sulfur oxidation intermediates. In the present work, the ability of A. thiooxidans DSM 26636 for the bioleaching of metals contained in five different spent catalysts was assessed by growing the culture in modified Starkey mineral medium (with elemental sulfur at 1%, w/v), and 1% (w/v) pulp density of each residue for up to 21 days at 30 °C and 150 rpm. Sulfur-oxidizing activity was periodically evaluated by determining sulfate concentration in the supernatants according to the NMX-k-436-1977 method. The production of sulfuric acid was assessed in the supernatants as well, by a titration procedure using NaOH 0.5 M with bromothymol blue as acid-base indicator, and by measuring pH using a digital potentiometer. On the other hand, Inductively Coupled Plasma - Optical Emission Spectrometry was used to analyze metal removal from the five different spent catalysts by A. thiooxidans DSM 26636. Results obtained show that, as could be expected, sulfuric acid production is directly related to the diminish of pH, and also to highest metal removal efficiencies. It was observed that Al and Fe are recurrently removed from refinery spent catalysts regardless of their origin and previous usage, although these removals may vary from 9.5 ± 2.2 to 439 ± 3.9 mg/kg for Al, and from 7.13 ± 0.31 to 368.4 ± 47.8 mg/kg for Fe, depending on the spent catalyst proven. Besides, bioleaching of metals like Mg, Ni, and Si was also obtained from automotive spent catalysts, which removals were of up to 66 ± 2.2, 6.2±0.07, and 100±2.4, respectively. Hence, the data presented here exhibit the potential of A. thiooxidans DSM 26636 for the simultaneous bioleaching of metals contained in spent catalysts from diverse provenance.

Previous work has demonstrated that Bacillus megaterium, besides showing an elevated resistance to heavy metals, possesses the ability to remove metals like Ni, Hg, and V from liquid media. Notably, Ni represents a highly valuable metal commonly found in industrial wastes, whose removal from environment is crucial, as it is considered a dangerous toxic metal. Thus, the aim of the present study was to determine Bacillus megaterium MNSH1-9K-1 resistance to Al, Ni, V, and Mo, metals that are commonly found in high metal content residues, and also evaluate its Ni removal capability from liquid medium. To this end, the microorganism was exposed to different metal concentrations, and its resistance was assayed by serial dilutions and viable count. Afterwards, MNSH1-9K-1 Ni resistance and removal capability was evaluated by ICP-OES. The results showed that this microorganism presents a Minimum Inhibitory Concentrations of 240, 2000, 35000 and >270000 ppm for Ni, Al, V, and Mo, respectively. Even more, MNSH1-9K-1 is able to remove up to 26 ppm of Ni. The results presented here may contribute to the knowledge regarding the application of this microorganism for the biotreatment of high metal content liquid and solid residues, mainly the ones containing Ni.

The present study evaluated the ability of organic acids (leaching agent) produced by three filamentous fungi coded as MNSS-AH-5, MV-AH-2 and MV-AH-1 obtained from tailings samples to remove Ni and V from spent catalyst at 16 % (w/v) pulp density. Organic acids were produced in 500 mL Erlenmeyer flasks containing 150 mL of sucrose media where flasks were inoculated with 10% (1x107 conidia/mL) of each fungus and incubated during 6 days at 30°C, 150 rpm. The leaching agent produced by MNSS-AH-5, MV-AH-2 and MV-AH-1 in sucrose media were assayed to remove Ni and V from spent catalyst at 16% (w/v) pulp density during 7 days at 30°C, 150 rpm. At the end of incubation, Ni and V content was evaluated in bio treated catalyst samples by ICP-EOS. Controls containing sucrose media were included in order to evaluate the action of culture media on leaching; all experiments were done in duplicated. Results showed that after 7 days of incubation, the organic acids produced by MNSS-AH-5 were able to leach 2525 mg/Kg of Ni corresponding to 21 %, not significance difference was observed for organic acids of MV-AH-2 and MV-AH-1. In the case of V, all bioleaching treatments presented statistical difference observing a V leaching of 10921.8, 11099.3 and 4757.5 mg/Kg corresponding to 23.5, 24 and 10% for MNSS-AH-5, MV-AH-2 and MV-AH-1 respectively. Isolate MNSS-AH-5 was identified as Acremonium sp., MV-AH-2 and MV-AH-1 were identified as belonging to genera Penicillium. Based on results, this study shows that leaching agent produced by fungi could be an excellent biological alternative for the removal of Ni and V spent catalyst.

The purpose of the present study was to investigate the ability ofMicrobacterium liquefaciensstrain MNSH2-PHGII-2, isolated from a Mexican silver mine, for removing Ni and V from spent catalyst at 80% (w/v) pulp density in a glass-column system at laboratory conditions. Firstly, microbial culture was adapted to spent catalyst at 0.1% (w/v) in liquid culture then, it was assayed by its ability to remove Ni and V from a spent catalyst in a glass-column system. Spent catalyst was packed at 80% (w/v) pulp density and inoculated at 20% (3x108CFU/ml); air was supplied at 80 ml/min and then incubated at 30°C during 14 days. Parameters such as microbial growth, pH, Ni and V residual concentrations, in catalyst, were determined at days 7 and 14. The result showed thatMicrobacterium liquefaciensstrain MNSH2-PHGII-2 in the glass-column system was able to remove 1007.4 mg/kg of Ni while V was removed at an extent of 5360.5 mg/kg. Microbial removal for other metals in catalyst was non-significant, that indicated the specificity ofMicrobacterium liquefaciensto remove Ni and V.

The present study evaluated 15 isolates obtained of environmental samples capable of tolerating high Ni and V concentrations. Those coded as MNSH2-PHGII-1, MNSH2-PHGII-2 and MV-PHGII-2 showed a minimum inhibitory concentration higher than 200 ppm for Ni and V and showed removal percentages corresponding to 84, 75 and 26% for Ni and 60, 55 and 20.3% for V, respectively, in liquid medium. When spent catalyst was added at 16% (w/v) pulp density, the highest Ni and V removal corresponded to MNSH2-PHGII-1 and MNSH2-PHGII-2, which were identified as Microbacterium oxydans and Microbacterium liquefaciens respectively, Microbacterium oxydans was able to remove Ni at the extent of 45.4% and V at 30.4% while Microbacterium liquefaciens removed Ni at 51% and V at 41.4% from the spent catalyst. The isolate MV-PHGII-2 identified also as Microbacterium oxydans showed the lowest removal for Ni and V corresponding to 16% and 9.5%, respectively. This is the first report where strains of Microbacterium were tested for their abilities to remove Ni and V from spent catalyst, suggesting its potential use in the treatment of this solid industrial waste.

Considering the progressive depletion of natural resources and the increasing environmental pollution, recovery of metals from spent catalysts has been gaining importance, as they can be an eco-friendly sour-ce of commercially valuable metals. The present study reports on the ability of three Bacillus spp. strains to remove Ni and V contained in a spent catalyst at 8% of pulp density (w/v). As modifications in the growth environment, like pH and the presence of diverse carbon sources, can cause changes in cell properties, the present study evaluated the effect of glucose presence in PHGII media on Ni and V removal from a spent catalyst. Assays were performed on PHGII liquid media, and on PHGII without glucose for 7 days. The maximum removal values obtained were 2542 mg/kg for Ni, and 3701 mg/kg for V for the isolate MV-9K-2 of Bacillus megaterium in the system, where PHGII was not added with glucose

The present study evaluated the microbial removal of sulfur from a solid industrial waste in liquid culture under laboratory conditions. The study involved the use of two bacteria Acidithiobacillus ferrooxidans ATCC 53987 and Acidithiobacillus thiooxidans AZCT-M125-5 isolated from a Mexican soil. Experimentation for industrial waste biotreatment was done in liquid culture using 125-mL Erlenmeyer flasks containing 30 mL Starkey modified culture medium and incubated at 30°C during 7 days. The industrial waste was added at different pulp densities (8.25-100% w/v) corresponding to different sulfur contents from 0.7 to 8.63% (w/w). Sulfur-oxidizing activity of the strain AZCT-M125-5 produced 281 and 262 mg/g of sulfate and a sulfur removal of 60% and 45.7% when the pulp density was set at 8.25 and 16.5% (w/v), respectively. In comparison, the strain A. ferrooxidans ATCC 53987 showed a lower sulfur-oxidizing activity with a sulfate production of 25.6 and 12.7 mg/g and a sulfur removal of 6% and 2.5% at the same pulp densities, respectively. Microbial growth was limited by pulp densities higher than 25% (w/v) of industrial waste with minimal sulfur-oxidizing activity and sulfur removal. The rate of sulfur removal for Acidithiobacillus thioxidans AZCT-M125-5 and Acidithiobacillus ferrooxidans ATCC 53987 was 0.185 and 0.0159 mg S g(-1) h(-1) with a pulp density of 16.5% (w/v), respectively. This study demonstrated that Acidithiobacillus thiooxidans AZCT-M125-5 possesses a high sulfur-oxidizing activity, even at high sulfur concentration, which allows the treatment of hazardous materials.

Microbacterium liquefaciens MNSH2-PHGII-2 is a nickel–vanadium-resistant bacterium isolated from mine tailings located in Guanajuato, Mexico. In PHGII liquid media, M. liquefaciens has the ability to remove 29.5 ppm of Ni and 168.3 ppm of V. The present study reports, for the first time in M. liquefaciens, the presence of the genes nccA (Ni–Co–Cd resistance), hant (high-affinity nickel transporter), smtA, a metal-binding protein gene, and VAN2 (V resistance), which showed an increased expression under exposure to 200 ppm of Ni and 200 ppm of V during the logarithmic growth phase of the microorganism in PHGII liquid media. Data about the expression profile of genes conferring metal resistance to M. liquefaciens can improve the knowledge of those mechanisms involved in the processes of Ni–V resistance and probably in Ni–V removal processes. Based on our data, we can suggest that M. liquefaciens has the potential to be used in the biological treatment of toxic wastes with high Ni and V content.

Solid culture with small amounts of low-quality raw coffee beans was used for total petroleum hydrocarbon (TPH) removal from a weathered and polluted soil. Soil contaminated with 58 000 mg kg −1 of TPH was treated with soil:coffee bean ratios of 98:2, 96:4, 94:6, and 92:8, at a C:N:P ratio of 100:10:1, 20% humidity, and 28 °C, for periods of 15, 60, and 90 days. The highest TPH removal (63%) was obtained with a soil/bean ratio of 98:2 over 15 days, corresponding with the highest rates of microbial respiration and the greatest increases in bacterial and fungal counts to 9 lnCFU and 6 lnCFU, respectively. Scanning electron microscopy showed high fungal colonization of coffee beans, with Mucor sp., Aspergillus sp., Aspergillus niger. , and Penicillium sp. growing on TPH as sole carbon source.

The remediation of drilling mud-polluted sites in the Southeast of Mexico is a top priority for Mexican oil industry. The objective of this work was to find a technology to remediate these sites. A field trial was performed by composting in biopiles, where four 1 ton soil-biopiles were established, one treatment in triplicate and one unamended biopile. Amended biopiles were added with nutrients to get a C/N/P ratio of 100/3/0.5 plus a bulking agent (straw) at a soil/straw ratio of 97/3. Moisture content was maintained around 30–35%. Results showed that, after 180 d, total petroleum hydrocarbon (TPH) concentrations decreased from 99 300 ± 23 000 mg TPH kg −1 soil to 5500 ± 770 mg TPH kg −1 for amended biopiles and to 22 900 ± 7800 mg TPH kg −1 for unamended biopile. An undisturbed soil control showed no change in TPH concentrations. Gas chromatographic analysis showed residual alkyl dibenzothiophene type compounds. Highest bacterial counts were observed during the first 30 d which correlated with highest TPH removal, whereas fungal count increased at the end of the experimentation period. Results suggested an important role of the straw, nutrient addition and water content in stimulating aerobic microbial activity and thus hydrocarbon removal. This finding opens an opportunity to remediate old polluted sites with recalcitrant and high TPH concentration.

The application of biological processes in restoring oil polluted sites is growing due to their efficiency in removing different classes of pollutants. The aim of this study was to determine the ability of microorganisms present in a drilling-waste polluted soil (36,200 mg TPH kg−1 soil) to remove weathered hydrocarbons under stimulated and non-stimulated soil conditions. The hypothesis under study was whether petroleum hydrocarbons removal could be enhanced by manipulating C/N ratio, water content and addition of three agroindustrial wastes. A Box-Behnken design was employed to evaluate the effect of each variable. Results demonstrated that, for orange peels and banana trunk treatments, the variable with the largest effect (p < 0.01) on hydrocarbon removal was the C/N ratio, indicating that higher ratio (100/3) improved removal (79.5–82%). The largest effect (p < 0.001) on hydrocarbon removal for pineapple wastes was observed with higher water content (60%) achieving the highest removal (89%). After 90 d...

The aim of this work was to isolate oil-degrading bacteria that use chitin or keratin as carbon sources from oil contaminated soils; and additionally to study if oil removal by these bacteria is enhanced when a chitinous or a keratinous waste is added to the culture media. To isolate the above-mentioned bacteria, 12 soil samples were collected close to an oil-well. Such soils showed unsuitable nutrients content, but their counts of heterotrophic bacteria ranged within 10(5)-10(8) CFU g(-1) soil, of which 0.1-77% corresponded to oil hydrocarbon-degrading ones. By sampling on plates, 109 oil-degrading bacterial isolates were obtained. Their keratinase and chitinase activities were then screened by plate assays and spectrophotometric methods, resulting in 13 isolates that were used to integrate two mixed cultures, one keratinolytic and the other chitinolytic. These mixed cultures were grown in media with oil, or oil supplemented with chicken-feathers or shrimp wastes. The oil-hydrocarbon removal was measured by gas chromatography. Results showed that keratinolytic bacteria were better enzyme producers than the chitinolytic ones, and that oil removal in the presence of chicken-feathers was 3.8 times greater than with shrimp wastes, and almost twice, in comparison with oil-only added cultures. Identification of microorganisms from the mixed cultures by 16S rDNA, indicated the presence of seven different bacterial genera; Stenotrophomonas, Pseudomonas, Brevibacillus, Bacillus, Micrococcus, Lysobacter and Nocardiodes. These findings suggest that the isolated microorganisms and the chicken-feather wastes could be applied to the cleaning of oil-contaminated environments, whether in soil or water.

Contamination of soil and water with petroleum hydrocarbons has significantly increased as a result of accidental spills, thus, several biological systems have been applied to cleanup and rehabilitate the negatively impacted regions. The present review discusses the fundamental principles required to understand the effectiveness of some bioremediation systems applied to soil and water contaminated with petroleum hydrocarbons and other organic pollutants. The practical aspects of several experimental approaches such as composting and soil amendment application, plant utilization and rhizosphere microbial activity as a keystone during phytoremediation, slurry bioreactors utilization, and potential utilization of microalgae to decontaminate wastewater, are also described.

Bioaugmented-assisted remediation of a hydrocarbon-polluted soil was performed in sealed serum bottles using a native and well adapted mixed culture consisting on S. liquefaciens and B. coagulans. The soil for this study was acidic (pH 3.8) with a total petroleum hydrocarbon (TPH) concentration of 220,000 mg/kg soil and a native microbial population of 2.0×10 5 CFU/g soil. This study examines a biological treatment to clean up petroleum-polluted soil using a mixed culture composed by S. liquefaciens and B. coagulans. C/N/P ratio, moisture and pH were adjusted to appropriate values to assist the biodegradation process. Results demonstrated that heterotrophic activity in microcosms was higher (1.9 mg/g) in bioaugmented microcosms compared with non-bioaugmented (1.3 mg/g). During all the incubation period only three strains were cultivated S. liquefaciens, B. coagulans and a non-identified yellow bacteria. The TPHs removal increased 12% in bioaugmented microcosms at the end of 74 days of treatment. In the case of aromatic and asphaltenic fractions the removals increased 12 and 10% respectively. During the first 35 days of incubation, TPHs removal correlates with the exponential phase of microbial growth. Our results showed that bioaugmented-assisted remediation of hydrocarbon-polluted soils in highly polluted and weathered sites are feasible.

The objective of this study was to determine the feasibility of bioremediation as a treatment option for an aged and chronically polluted drilling waste soil located at the Southeast of Mexico. The polluted drilling-waste site with a mean total petroleum hydrocarbon concentration (TPHs) of 39,397 +/- 858 mg/kg was treated with one dose of a nutrient-surfactant commercial product at 40 mg/kg soil and two doses of H2O2 (50 and 100 mg H2O2/kg soil). In this study, the parameters that were monitored include soil respiration, heterotrophic and hydrocarbon-degrading bacteria as biological indicators, catalase and dehydrogenase activities, and TPHs degradation as decontamination parameters. The results demonstrated that the microbial activities can be stimulated in a polluted drilling-waste site by the addition of H2O2 and commercial product, thereby resulting in increasing TPHs degradation. These aspects must be taken into account when biodegradation studies involve the application of a commercial product.