Microbial bioprocessing and functional magnetic nanomaterials

The aim of this project is to understand and further improve current biomanufacturing strategies for the biological production of magnetosomes, which are naturally produced in magnetotactic bacteria (MTB). Magnetosomes are sub-cellular nanoscale organelles that are normally arranged in one or more highly ordered 'compass needle-like' chains of single-domain permanently ferrimagnetic magnetite (Fe3O4) or greigite (Fe3S4) crystals (35-120 nm diameter) each wrapped in a biological phospholipid membrane. Magnetosomes have tremendous potential for biotechnological applications and have a great probability to become the next generation of functional materials. They represent an attractive alternative to existing commercially available chemically-synthesized magnetic nanoparticles because of the unique properties that they present: narrow size distribution, uniform morphology, high crystal purity, permanent magnetic character, high heating capacity, low aggregation tendency, ready dispersion in aqueous solution, facile functionalization, high biocompatibility, low toxicity and high specific absorption rates. One of the most used and studied bacterial strains for producing magnetosomes is Magnetospirillum gryphiswaldense MSR-1 because it can be cultured at higher cell densities than other MTB species. All previous studies reported low magnetosome formation yield. Therefore, an evaluation of the effects of critical bioprocess parameters in fermentation experiments that limit biomass and magnetosome yields must be done. M. gryphiswaldense synthetizes these nanoparticles through a biomineralization process in which soluble iron is crystallised into a magnetic mineral. However, biomineralization of magnetic iron minerals is still poorly understood. Some critical parameters in the biomineralization process are O2 availability, understanding the dynamics of how iron ions enter the cell and the intracellular pool of chelatable iron. It is also important to understand the physiological and metabolic stress parameters of MTB strains for the development of a controlled strategy to enhance cell growth. The physiology of M. gryphiswaldense has not been sufficiently studied in high-cell density cultures and so little is known about the parameters that limit biomass and magnetosome yields. Monitoring physiological stress indicators is essential for being able to implement rapid analytical techniques for future industrial production. Employing flow cytometry methods had been proven to be an efficient tool to evaluate a range of physiological and stress parameters such as cell morphology, aspects of metabolism and the accumulation of intracellular polyhydroxyalkanoate (PHA). Finally, the purification of magnetosomes using scalable and green methods and the formulation of magnetosome cocktails that are biocompatible would be interesting to develop for future potential applications.