Greater Mexico City is one of the largest urban centers in the world, with an estimated population by 2010 of more than 20 million inhabitants. In urban areas like this, biological material is present at all atmospheric levels including live bacteria. We sampled the low atmosphere in several surveys at different points by the gravity method on LB and blood agar media during winter, spring, summer, and autumn seasons in the years 2008, 2010, 2011, and 2012. The colonial phenotype on blood agar showed α, β, and γ hemolytic activities among the live collected bacteria. Genomic DNA was extracted and convenient V3 hypervariable region libraries of 16S rDNA gene were high-throughput sequenced. From the data analysis, Firmicutes, Proteobacteria, and Actinobacteria were the more abundant phyla in all surveys, while the genera from the family Enterobacteriaceae, in addition to Bacillus spp., Pseudomonas spp., Acinetobacter spp., Erwinia spp., Gluconacetobacter spp., Proteus spp., Exiguobacterium spp., and Staphylococcus spp. were also abundant. From this study, we conclude that it is possible to detect live airborne nonspore-forming bacteria in the low atmosphere of GMC, associated to the microbial cloud of its inhabitants.

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.

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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.

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.