| Magnetotactic bacteria (MTB) are motile prokaryotes that have the ability to propel along geomagnetic field lines. Hallmarks of MTB are intracellular magnetosomes, which are magnetic crystals of either iron oxide, magnetite (Fe3O4), or iron sulfide, greigite (Fe3S4) or iron pyrite (FeS2) enveloped by a phospholipid bilayer membrane. It can be found that there are many similar properties between Acidithiobacillus ferrooxidans (At. ferrooxidans) and MTB, such as distribution, morphological types, motility, Gram stain, trophic type, medium composition, requiring oxygen type and growth temperature. It has been reported that At. ferrooxidans is able to synthesize intracellular electron dense magnetite but is only weakly magnetotactic. In contrast to other MTB, the information available on the magnetic properties of At. ferrooxidans is very sparse.In this work, we present a detailed magnetic study of At. ferrooxidans grown in pure culture. The cells were examined by transmission electronmicroscopy (TEM), vibrating sample magnetometer (VSM), magneto-thermal gravity analysis (MTGA), low temperature magnetometry, and Mossbauer spectroscopy analysis. The results revealed that:the bacteria cultured in 9K medium is able to synthesize magnetosomes; the number of magnetosomes in single cell is about 2; the dry and wet cells were adsorbed by magnet; the bacteria showed magnetotaxis in the semisolid plate and under the light microscope with additional magnetic field; the calcined bacteria exhibited ferromagnetic behavior with a coercivity of 20.17 mT and remnance of 0.62 emu/g; the curic temperature (Tc) of calcined cells was about 453.96℃; the low-temperature field-cooled (FC) and zero-field cooled (ZFC) magnetization curves split near 120 K; there are no magnetosome chains in At. ferrooxidans, for the delta ratio (δFC/δZFC) is between 1 and 2 (1.27); and the mineral type of magnetosomes in At. ferrooxidans was magnetite.Then, the effects of different factors, such as iron sources, nitroge sources, temperature, initial pH and atmospheric oxygen concentrations, on the growth of At. ferrooxidans and the synthesis of magnetosomes were investigated. Moreover, the orthogonal design of experiment was used to optimize the condition of At. ferrooxidans growth and magnetosomes synthesizing. The results indicated that the optimized conditions of At. ferrooxidans growth and magnetosomes synthesizing were not identical. The optimized conditions for the growth of At. ferrooxidans were found to be: FeSO4 120 mM, (NH4)2SO4 3.0 g/L, temperature 30℃, initial pH 1.75, and 20%loadings. However, the optimized conditions for magnetosomes synthesizing of At. ferrooxidans were found to be:FeSO4160 mM, (NH4)2SO4 2.4 g/L, temperature 20℃, initial pH 1.75, and 50%loadings. Initial purification of the magnetosomes can be accomplished by washing eight to ten times with HEPES buffer, along with lysozyme treatment, low-temperature ultrasonication, and magnet collection. The properties of magnetosomes such as crystalline, surface functional group, vitro cytotoxicity, genotoxicity and blood toxicity were investigated. The X-ray diffraction (XRD) assay indicated that the magnetic nanocrystal within the magnetosomes is consisted of magnetite. Fourier transform infrared spectroscopy (FTIR) analysis revealed the existence of different chemical groups on the surface of the magnetosomes. MTT assay revealed that the magnetosomes had no cytoxicity in the experimantal concentration range. Hemolysis study showed that the magnetosomes had no hemolysis activity. The micronucleus frequency of magnetosomes showed a significant (p<0.01) decrease compared to the positive control. Additionally,38 genes involved in the biomineralization of magnetosomes were collected in this work, and the sequences were compared with the whole genome of type strain At. ferrooxidans ATCC 23270 by bioinformatics. Temporal expression profiles of mpsA gene which had highest homology in different treatment were examined by RT-PCR. The expression level of mpsA was significantly affected by ferrous concentration, oxygen concentration, and static magnetic field strength.At. ferrooxidans is resistant to heavy metals and metalloids at concentrations in the milligram per liter range, which is considered toxic for other microorganisms. Although the potential of At. ferrooxidans as a biosorbent for various metals, including Ni2+, Cd2+, Zn2+, Pb2+ and Cu2+ has been reported, there is a lack of information about the removal of arsenic species by At. ferrooxidans.The biosorption characteristics of arsenite (iAsⅢ), monomethyl arsonate (MMAⅤ) and dimethylarsinic acid (DMAⅤ) from aqueous solution by At. ferrooxidans were investigated as a function of pH, contact time, initial arsenic concentration, biomass dosage and temperature in this study. Results indicated that the adsorption process was rapid and maximum sorption capacities were achieved within 30 min for iAsⅢand 40 min for MMAⅤand DMAⅤ. Langmuir model fitted better than Freundlich model to the equilibrium data. The Langmuir maximum biosorption capacity of iAsⅢ, MMAⅤand DMAⅤwas found to be 293.25,333.33 and 333.33μg/g, respectively. Analysis of kinetic data showed that the biosorption processes of iAsⅢ, MMAⅤand DMAⅤinvolved pseudo-second-order kinetics. The thermodynamic parameters of the biosorption process showed that the adsorption of iAsⅢ, MMAⅤand DMAⅤonto At. ferrooxidans was feasible, spontaneous and endothermic under the examined conditions. FTIR analysis indicated that various chemical groups were involved in the biosorption process. These results reveal that At. ferrooxidans has a potential for use in removing arsenic from aqueous solutions. |
PDF Full Text Request