A new technique to evaluate Acidithiobacillus thiooxidans growth during a bioleaching process based on DNA quantification.

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.

Nanosilver gel as an endodontic alternative against Enterococcus faecalis in an in vitro root canal system in Mexican dental specimens.

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.

czcD gene from Bacillus megaterium and Microbacterium liquefaciens as a potential nickel-vanadium soil pollution biomarker.

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.

Potential use of Bacillus genera for metals removal from spent catalysts.

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 their ability to remove metals contained in a spent catalyst. Seventeen isolates were obtained; among them seven presented a minimum inhibitory concentration (MIC) higher than 200 mg/L of Ni2+ and V5+ each. Nickel and Vanadium removal was evaluated in 9 K liquid medium added with spent catalyst at 16% (s/v) pulp density and incubated at 30 °C, 150 rpm for 7 days. Only three isolates which were coded as PRGSd-MS-2, MNSH2-AH-3, and MNSS-AH-4 showed a significant removal at the end of treatment corresponding in mg kg-1 (or percentage metal removal) of 138 (32%), 123 (29%), and 101 (24%) for Ni, respectively; and 557 (26%), 737 (34%), and 456 (21%) mg kg-1 for V, respectively. The same isolates were capable to remove also Al, Fe, As, and Mg at different extent. Cell morphology changes were observed, in comparison to the control system at the end of biological treatment as a higher quantity of spores for MNSH2-AH-3, 2 µm cells in pairs for MNSS-AH-4, also long chain-vegetative cells having inclusions into the cell surface were observed for PRGSd-MS-2. The three isolated microorganisms were identified by sequencing of the 16S gene as Bacillus thuringiensis, Bacillus megaterium, and Bacillus sp, respectively, suggesting its potential use in the treatment of this solid industrial waste.

Metal removal and morphological changes of B. megaterium in the presence of a spent catalyst.

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.

Expression Changes in Metal-Resistance Genes in Microbacterium liquefaciens Under Nickel and Vanadium Exposure.

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.

Identification of Bacillus megaterium and Microbacterium liquefaciens genes involved in metal resistance and metal removal.

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(-1) Ni and 2165 ± 77 mg·kg(-1) V. 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.

Expression Analysis of Ni- and V-Associated Resistance Genes in a Bacillus megaterium Strain Isolated from a Mining Site.

Bacillus megaterium strain MNSH1-9K-1 was isolated from a mining site in Guanajuato, Mexico. This B. megaterium strain presented the ability to remove Ni and V from a spent catalyst. Also, its associated metal resistance genes nccA, hant, VAN2, and smtAB were previously identified by a PCR approach. The present study reports for the first time, in B. megaterium, the changes in the expression of the genes nccA (Ni-Co-Cd resistance); hant (high-affinity nickel transporter); smtAB, a metal-binding protein gene; and VAN2 (V resistance) after exposure to 200 ppm of Ni and 200 ppm of V during the stationary phase of the microorganism in PHGII liquid media. The data presented here may contribute to the knowledge of the genes involved in the Ni and V resistances of B. megaterium, and the possible pathways implicated in the Ni-V removal processes, which may be potentiated for the biological treatment of high metal content residues.

Airborne Bacterial Diversity from the Low Atmosphere of Greater Mexico City.

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, ß, 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.

Microbacterium oxydans and Microbacterium liquefaciens: a biological alternative for the treatment of Ni-V-containing wastes.

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.

Microbial treatment of sulfur-contaminated industrial wastes.

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.