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
|Acute bacterial growth inhibition||Acute bacterial respiratory inhibition|
|EC10b||3 h EC50c|
|Molybdenum trioxide (pure)
|Molybdenum trioxide (tech)
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.