Bacteria

The toxicity of molybdate to freshwater and marine organisms. III. Generating additional chronic toxicity data for the refinement of safe environmental exposure concentrations in the US and Europe

The freshwater and marine long-term ecotoxicity datasets used in the European REACH registration dossiers for molybdenum and molybdenum compounds resulted in the derivation of a HC5,50%,freshwater (38.2mgMo/L) and HC5,50%,marine (5.70mgMo/L) by means of the statistical extrapolation method. Both datasets, however, did not meet the US-EPA information requirements for deriving Final Chronic Values (FCV) that were based on chronic data. US-EPA compliance was achieved by generating chronic no-effect data for the freshwater benthic amphipod Hyalella azteca and the marine inland silverside fish Menidia beryllina, using sodium molybdate dihydrate as test substance. A 42d-EC10 of 44.6mgMo/L for reproduction was determined in a water-only exposure with H. azteca. For M. beryllina, a 37d-NOEC of 139mg mMo/L for standard length and blotted wet weight was found. Other endpoints (e.g., survival, hatching success) proved to be less sensitive. Data were added to the existing chronic toxicity datasets, together with new long-term no-effect values that were identified in open literature for brown trout Salmo trutta, the marine alga Isochrysis galbana, the marine snail Nassarius dorsatus and the marine barnacle Amphibalanus amphitrite. The updated data sets resulted in a freshwater and marine HC5,50% of 35.7 and 6.85mgMo/L, respectively. The same data sets were also used for the determination of US-EPA FCVs, where the FVCfreshwater was 36.1mg/L, and the FCVmarine was 3.85mgMo/L. As the Final Plant Values for both aquatic environments were higher than their respective FCVs, the Criterion Continuous Concentration (CCC) for molybdenum is equal to the FCV.

Heijerick, D. G., and Carey, S.,The toxicity of molybdate to freshwater and marine organisms. III. Generating additional chronic toxicity data for the refinement of safe environmental exposure concentrations in the US and Europe, The Science of the total environment, 2017, 609, 420-428.

 

Precision editing of the gut microbiota ameliorates colitis

Inflammatory diseases of the gastrointestinal tract are frequently associated with dysbiosis(1-8), characterized by changes in gut microbial communities that include an expansion of facultative anaerobic bacteria of the Enterobacteriaceae family (phylum Proteobacteria). Here we show that a dysbiotic expansion of Enterobacteriaceae during gut inflammation could be prevented by tungstate treatment, which selectively inhibited molybdenum-cofactor-dependent microbial respiratory pathways that are operational only during episodes of inflammation. By contrast, we found that tungstate treatment caused minimal changes in the microbiota composition under homeostatic conditions. Notably, tungstate-mediated microbiota editing reduced the severity of intestinal inflammation in mouse models of colitis. We conclude that precision editing of the microbiota composition by tungstate treatment ameliorates the adverse effects of dysbiosis in the inflamed gut.

W. H. Zhu, M. G. Winter, M. X. Byndloss, L. Spiga, B. A. Duerkop, E. R. Hughes, L. Buttner, E. D. Romao, C. L. Behrendt, C. A. Lopez, L. Sifuentes-Dominguez, K. Huff-Hardy, R. P. Wilson, C. C. Gillis, C. Tukel, A. Y. Koh, E. Burstein, L. V. Hooper, A. J. Baumler, and S. E. Winter,Precision editing of the gut microbiota ameliorates colitis, Nature, 2018, 553, 208-+.

               

Self-Healing, antibacterial and sensing nanoparticle coating and its excellent optical applications

Self-healing, antibacterial and metal-ion sensing coatings with nanoparticles were developed using layer-by-layer (LbL) self-assembly technique via host-guest interaction. The coatings consist of MoS2 nanosheets, beta-cyclodextrin (beta-CD)-modified poly (ethylenimine) (PEI) and adamantane (AD)modified poly (acrylic acid) (PAA). Damages to conventional coatings results in cracking and affects the coatings' ability to maintain antibacterial and sensing qualities. The prepared MoS2/beta-CD-PEI/AD-PAA self-healing coatings are not only able to greatly suppress bacterial adhesion and have excellent antibacterial property, particularly under UV light irradiation, but also have a longtime service time. Moreover, the self-healing coatings first applied the fluorescence quenching for detecting heavy metals (Co2+). Fluorescence spectra demonstrated that a linear relationship existed between the fluorescence intensity and the Co2+ concentration with 0 similar to 0.1 µg/mL and the detection limit of Co2+ is 0.018 mg/mL. Therefore, the nanoparticle multilayer polyelectrolyte hybrid coatings have a potential application in food industries. (C) 2017 Elsevier B.V. All rights reserved.

H. Y. Xuan, W. Dai, Y. X. Zhu, J. Y. Ren, J. H. Zhang, and L. Q. Ge,Self-Healing, antibacterial and sensing nanoparticle coating and its excellent optical applications, Sensors and Actuators B-Chemical, 2018, 257, 1110-1117.

 

MoS2-TiO2 Nanocomposite with Excellent Adsorption Performance and High Antibacterial Activity

The need of multifunctional advanced materials, facilitating clean and sustainable environment is the key issue from the perspective of materials scientists. This study demonstrates facile and scalable synthesis of MoS2-TiO2 nanocomposites and their excellent performance as nanoadsorbents and antibacterial agent. The synthesized composites, with different loading of MoS2 and TiO2, were examined by XRD, XPS, RAMAN, FESEM and HRTEM for structural, chemical and morphological details. The MoS2-TiO2 nanocomposite displays adsorption capacity as high as 364.56mg.g(-1) for methylene blue (MB) at room temperature and the kinetic data reveal that the adsorption process of MB is well-matched with the pseudo-first-order model. The MoS2-TiO2 nanocomposites, with different morphology, have shown their capability as an organic dye scavenger with high speed and efficiency. Moreover the composites execute considerable antibacterial activity against Gram positive Staphylococcus aureus and Gram negative Escherichia coli bacteria. Thus the presented MoS2-TiO2 nanocomposite, with synergistic performance, shows huge potential in the search of multifunctional smart materials for future technology to address environment issues.

A. Pal, T. K. Jana, T. Roy, A. Pradhan, R. Maiti, S. M. Choudhury, and K. Chatterjee, MoS2-TiO2 Nanocomposite with Excellent Adsorption Performance and High Antibacterial Activity, Chemistryselect, 2018, 3, 81-90.

 

Bacteria MoS2 toxicity

Comparative toxicity of Cd, Mo, and W sulfide nanomaterials toward E-coli under UV irradiation

In this study, the phototoxicity of cadmium sulfide (CdS), molybdenum disulfide (MoS2), and tungsten disulfide (WS2) nanoparticles (NPs) toward Escherichia coil (E. coli) under UV irradiation (365 nm) was investigated. At the same mass concentration of NPs, the toxicity of three NPs decreased in the order of CdS > MoS2 > WS2. For example, the death rates of E. coil exposed to 50 mg/L CdS, MoS2, and WS2 were 96.7%, 38.5%, and 31.2%, respectively.
Transmission electron microscope and laser scanning confocal microscope images of E. coli exposed to three NPs showed the damage of cell walls and release of intracellular components. The CdS-treated cell wall was more extensively damaged than those of MoS2 treated and WS2-treated bacteria.
WS2 and MoS2 generated superoxide radical (O2.—), singlet oxygen 1O2, and hydroxyl radical under UV irradiation, CdS produced only O2- and 1O2. CdS and WS2 released ions under UV irradiation, while MoS2 did not. Reactive oxygen species (ROS) generation and toxic ion release jointly resulted in the antibacterial activities of CdS and WS2. ROS generation was the dominant toxic mechanism of MoS2 toward the bacteria. This study highlighted the importance of considering the hazardous effect of sulfide NPs after their release into natural waters under light irradiation condition. (C) 2017 Elsevier Ltd. All rights reserved.

Shang, E. X., Niu, J. F., Li, Y., Zhou, Y. J., and Crittenden, J. C.,Comparative toxicity of Cd, Mo, and W sulphide nanomaterials toward E-coli under UV irradiation, Environmental Pollution, 2017, 224, 606-614.

 

Optimization and maximization of hexavalent molybdenum reduction to Mo-blue by SERRATIA SP strain MIE2 using response surface methodology

Molybdenum has long been known to be toxic to ruminants, but not to humans. However, more recently it has been increasingly reported that molybdenum shows toxic effects to reproductive organs of fish, mouse and even humans. Hence, its removal from the environment is highly sought after. In this study, response surface methodology (RSM) was successfully applied in the optimization and maximization of Mo6+ reduction to Mo-blue by Serratia sp. MIE2 for future bioremediation application. The optimal conditions predicted by RSM were 20 mM molybdate, 3.95 mM phosphate, pH 6.25 and 25 g l-1 sucrose with absorbance of 19.53 for Mo-blue production measured at 865 nm. The validation experimental run of the predicted optimal conditions showed that the maximum Mo-blue production occurred at absorbance of 20.87, with a 6.75 % deviation from the predicted value obtained from RSM. Molybdate reduction was successfully maximized using RSM with molybdate reduction before and after optimization using RSM showing Mo-blue production starting at the absorbance value of 10.0 at 865 nm going up to an absorbance value above 20.87. The modelling kinetics of Mo6+ reduction showed that Teissier was the best model, with calculated P-max, K-s and K-i values of 1.97 Mo-blue per hour, 5.79 mM and 31.48 mM, respectively.

bin Halmi, M. I. E., Abdullah, S. R. S., Wasoh, H., Johari, W. L. W., Ali, M. S. B., Shaharuddin, N. A., and Shukor, M. Y.,Optimization and maximization of hexavalent molybdenum reduction to Mo-blue by Serratia sp strain MIE2 using response surface methodology, Rendiconti Lincei-Scienze Fisiche E Naturali, 2016, 27, 697-709.

Modelling the kinetics of hexavalent molybdenum (Mo6+) reduction by the SERRATIA sp strain MIE2 in batch culture

In the present work, the kinetics of hexavalent molybdenum reduction by the Serratia sp. strain MIE2 were investigated using several kinetic models, such as Monod, Haldane, Teissier, Aiba, Yano, Han and Leven-spiel and Luong. The statistical analysis showed that the best model was Teissier, which had the lowest RMSE and AICc values, the highest adjusted R-2 values, and an F test and with a bias factor and an accuracy factor nearest to unity (1.0). The calculated value for the Teissier constants, such as p(max), K-s and K-i, was 0.506 mu mol Mo-blue h(-1), 6.53 mM and 29.41 mM, respectively. The effect of heavy metals showed that hexavalent molybdenum reduction by the strain MIE2 was inhibited by silver, mercury and copper with a total inhibition of 96, 97, and 45 %, respectively, at a concentration of 1 ppm. Otherwise, the Mo-reducing enzyme was inhibited by mercury and zinc with an inhibition of 88 and 65 %, respectively. Most of the respiratory inhibitors did not inhibit the Mo-reducing enzyme activity, indicating that the respiratory system in this bacterium is not the site of the hexavalent molybdenum reduction. The results obtained from this study could be useful for estimating the relationship between molybdenum-blue production and the molybdate concentration, which may be important during the up scaling of the molybdenum bioremediation process.

Halmi, M. I. E., Abdullah, S. R. S., Johari, W. L. W., Ali, M. S. M., Shaharuddin, N. A., Khalid, A., and Shukor, M. Y.,Modelling the kinetics of hexavalent molybdenum (Mo6+) reduction by the Serratia sp strain MIE2 in batch culture, Rendiconti Lincei-Scienze Fisiche E Naturali, 2016, 27, 653-663.

NEGATIVE STAINING and Transmission Electron Microscopy of Bacterial Surface Structures

Negative staining is an essential and versatile staining technique in transmission electron microscopy that can be employed for visualizing bacterial cell morphology, size, and surface architecture at high resolution. Bacteria are usually transferred by passive electrostatic adsorption from suspensions in physiological saline onto suitable hydrophilic support films on electron microscopic grids. There they are contrasted, or "stained," by heavy metal ions in solution such as tungsten, uranyl, molybdate, or vanadate compounds. Here, I describe how to visualize the interaction between the bacterial M1 protein and complement factors C1q and C3 on the surface of group A streptococcus by negative staining with uranyl formate on carbon support films. The methodology should be generally applicable to the study of a large number of other bacteria-protein interactions.

Morgelin, M.,Negative Staining and Transmission Electron Microscopy of Bacterial Surface Structures, Methods in molecular biology (Clifton, N.J.), 2017, 1535, 211-217.

Investigating the Influence of MoS2 Nanosheets on E-COLI from Metabolomics Level

Molybdenum disulfide, a type of two-dimensional layered material with unique properties, has been widely used in many fields. However, an exact understanding of its toxicity remains elusive, let alone its effects on the environmental microbial community. In this study, we utilized metabolomics technology to explore the effects of different concentrations of molybdenum disulfide nanosheets on Escherichia coli for the first time. The results showed that with increasing concentration of molybdenum disulfide nanosheets, the survival rate of Escherichia coli was decreased and the release of lactic dehydrogenase was increased. At the same time, intracellular concentrations of reactive oxygen species were dramatically increased. In addition, metabolomics analysis showed that high concentrations of molybdenum disulfide nanosheets (100, 1000 mu g/mL) could significantly affect the metabolic profile of Escherichia coli, including glycine, serine and threonine metabolism, protein biosynthesis, urea cycle and pyruvate metabolism. These results will be beneficial for molybdenum disulfide toxicity assessment and further applications.

Wu, N., Yu, Y. D., Li, T., Ji, X. J., Jiang, L., Zong, J. J., and Huang, H.,Investigating the Influence of MoS2 Nanosheets on E-coli from Metabolomics Level, Plos One, 2016, 11.

 

IMOA Toxicological Testing Programme: Bacteriaa
SubstanceToxicity/ mg/l
Acute bacterial growth inhibitionAcute bacterial respiratory inhibition
EC10b3 h EC50c
Molybdenum trioxide (pure) d 820
Molybdenum trioxide (tech) d 3000
Ammonium dimolybdate 13  
Sodium molybdate 50  

Notes

a There are no EC criteria for bacterial toxicity. It is however factored into the German Water Hazard Classification. Under the German classification scheme, which takes into account fish, mammal and bacterial toxicity, the materials tested would give a maximum Water Hazard Classification of 1(weak hazard for waters).

b The EC10 is the concentration that causes a 10% reduction in turbidity. Test culture incubated with various concentrations of test substance for 18 hours. Turbidity measured by light transmission.

c The EC50 is the concentration that causes a 50% reduction in respiration. Test culture and test substance were left in contact for 30 minutes and three hours. At the end of each time period the dissolved oxygen content of the solution was measured.

d Growth inhibition is determined by the decrease in turbidity of test solution. Therefore, this method cannot be used on insolubles.