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The high levels of toxicity generated by the heavy metal content in industrial wastes has generated environmental and health concerns. One of the strategies to reduce the metallic load is the use of sulfur-oxidizing bacteria, due to its ability to produce sulfuric acid involved in the metal leaching. The aim of this research was to evaluate the growth of Acidithioobacillus thiooxidans DSM 26636 and its ability to leach metals from slags and ashes from coal combustion wastes. Microbial growth was monitoring by sulfate and sulfuric acid production. The metal content in slags and fly ashes was determined by ICP-OES. The experiments were carried out during 21 days at 30°C, 150 rpm in 125 mL Erlenmeyer flasks containing 30 mL of Starkey media added with 1% (w/v) of elemental sulfur and 1% (w/v) of slags or ashes. Results showed that Acidithioobacillus thiooxidans was able to leach V, Fe, Mg, Al, Si and Ni from slags. For fly ashes, metal leaching was Al, Ni, Sn, Mg, Zn and Si. Summarizing, Acidithioobacillus thiooxidans could be used for the leaching of different metals contained in wastes from carbon combustion plant. Mexican Journal of Biotechnology 2018, 3(3):54-67 RESUMENLos 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 metálica en estos residuos podría ser mediante el uso de bacterias sulfooxidantes debido a que tienen la habilidad de oxidar azufre y producir ácido sulfúrico, el cual está implicado en la lixiviación de metales. Así, el objetivo de la presente investigación fue evaluar el crecimiento de Acidithioobacillus thiooxidans DSM26636 y su habilidad de lixiviar metales de escorias y cenizas de una planta de combustión de carbón. El crecimiento microbiano fue monitoreado mediante la producción de sulfatos y ácido sulfúrico. El contenido de metales en las escorias y cenizas se determinó mediante ICP-OES. Los experimentos se llevaron a cabo durante 21 días 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 lixiviación de metales contenidos en residuos de escorias y cenizas provenientes de una planta de combustión de carbón.

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.

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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.

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