Enhancing magnetosome biomanufacturing: understanding biomineralization and process development

Abstract

Magnetosomes, membrane-bound magnetic nanocrystals produced by magnetotactic bacteria, offer a promising alternative to chemically synthesized magnetic nanoparticles due to their unique properties, enabling great potential in nanobiotechnology and biomedicine. However, several challenges hinder their large-scale production, including limited understanding of the biomineralization processes, cell physiology, batch-to-batch reproducibility, and lack of rapid and efficient characterization techniques. This thesis addresses these challenges by exploring ironuptake and its role in biomineralization, assessing the impact of oxidative stress on magnetosome formation, and evaluating cell disruption techniques on magnetosome chain integrity. Correlative microscopy, combined with a range of analytical methods, was employed to elucidate magnetosome biomineralization and the associated physiological changes of Magnetospirillum gryphiswaldense MSR-1 under various stress conditions. The research revealed a direct correlation between the labile Fe2+ pool size and magnetosome content, as higher intracellular iron concentrations were associated with increased magnetosome production. An intracellular iron pool, distinct from magnetite, was identified, being present throughout all stages of biomineralization. The potential role of magnetosomes in mitigating oxidative stress is further evidenced as magnetosome-producing cells maintained high levels of intracellular iron with minimal oxidative stress, while non-producing cells exhibited reduced magnetosome and iron content alongside elevated reactive oxygen species levels. The observed changes in MSR-1 cell morphology and viability under external stress conditions highlight the importance of monitoring physiological changes to enhance bioprocess efficiency and robustness, crucial for the production of high-quality magnetosomes. Furthermore, downstream processing technologies were shown to compromise magnetosome chain integrity, essential for certain applications. Among the tested disruption techniques, high-pressure homogenization was found to be the most effective in preserving magnetosome chain length, while nano-flow cytometry emerged as a promising technique for rapid quality assessment of single-magnetosome preparations. The findings contribute to a broader understanding of magnetosome production, emphasizing the importance of optimizing culture conditions and developing reliable characterization methods.