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Our lab was the first to report that Bacillus atrophaeus spores have intrinsic magnetism, and it was demonstrated that the magnetic susceptibility is sufficient to separate and deposit these spores on glass slides via a magnetic deposition system (Melnik et al. 2007). Surprisingly, Mn was the only paramagnetic element found in the spores, as indicated by Energy Dispersive Spectroscopy (EDS) analysis; but Mn is lacking in vegetative cells or other nonmagnetic spores. Moreover, magnetic susceptibility of different Mn oxides varies significantly, suggesting that the magnitude of a spore’s paramagnetism can differ based on a number of factors, including level of oxidation and time of sporulation. Experimentally, variation in the magnitude of paramagnetism was observed from batch to batch, and studies were conducted to further understand this variation including elemental quantification, optimization of the culturing, sporulating condition, and genetic studies.By adding polystyrene microparticles, which are of a very different size and magnetic susceptibility than spore clusters, the accuracy of Cell Track Velocitimetry (CTV) to measure and calculate magnetic susceptibility was explored and is reported. With the combination of CTV and X-ray Photoelectron Spectra, the oxidation state of Mn on spores and its imparting magnetic susceptibility to the spores was quantified, and the Mn per spore cluster was calculated. The calculation was consistent with the result from Inductively Coupled Plasma- Mass Spectrometry independent measurements. Different metal ion concentrations, oxygen availability and heat shock effects were examined during fermentation and Mn concentration was found to be the only factor that influenced the paramagnetism. Using these optimization studies, the Mn concentration was doubled in the media and the fermentation was scaled-up to 4 L using Biostat B bioreactor, and reliable magnetic spores were obtained. Potential applications of paramagnetic spores were also discussed: separation from various liquid food and adsorption of heavy metal ion from waste water. The intrinsic magnetism enabled the spores to be separated from air or liquid food, such as milk and chicken broth. However, spores couldn’t be separated from juice probably due to the low pH, in which the spores lost their paramagnetism. Interesting, the magnetism of spores recovered after adding Mn. Since spores could survive a sterilization process, the effect of sterilization on spores’ magnetism was examined. It turned out that the process didn’t alter the magnetic susceptibility of spores dramatically and surviving spores could be separated through the magnetic deposition system. |
