Impact of oxidative stress on Magnetospirillum gryphiswaldense MSR-1 physiology and magnetosome biomineralization at the single-cell level

Abstract

Magnetotactic bacteria, such as Magnetospirillum gryphiswaldense MSR-1, naturally produce magnetosomes—intracellular magnetic nanoparticles that enable navigation within geomagnetic fields. Magnetosomes hold significant potential for biomedical and biotechnological applications; however, key aspects of their biomineralization remain poorly understood. This study investigates how oxidative stress, induced by hydrogen peroxide and iron, influences magnetosome formation and bacterial physiology under aerobic and microaerobic conditions. Single-cell advanced microscopy and high-throughput techniques revealed that microaerobic conditions supported robust magnetosome production and larger magnetite crystals while maintaining low oxidative stress levels. In contrast, aerobic conditions suppressed magnetosome formation, reduced intracellular iron content, and increased reactive oxygen species (ROS) levels. High extracellular iron enhanced the formation of longer magnetosome chains in microaerobic cultures without causing toxicity but reduced cell viability under aerobic conditions. Hydrogen peroxide exposure caused mild damage and a 25% viability drop in magnetosome-producing cells but led to severe damage and an 80% viability drop in non-magnetosome-producing cells, along with chain fragmentation and smaller magnetite crystals. These results suggest that magnetosome-producing cells exhibit greater resilience to oxidative stress, potentially due to ROS scavenging properties of magnetosomes, and highlight the intricate interplay between oxidative stress, iron regulation, and magnetosome biomineralization. Single-cell analysis revealed heterogeneity in physiological responses, further demonstrating the complexity of these processes. These findings underscore the importance of monitoring physiological changes during production processes to enhance the efficiency and robustness of magnetosome synthesis. The insights gained provide a foundation for improving bioprocesses for large-scale production of high-quality magnetosomes, advancing their applications in biomedicine and biotechnology. IMPORTANCE Magnetotactic bacteria (MTB) are fascinating microorganisms with the capacity to produce iron oxide nanomagnets, namely magnetosomes. These nanomagnets passively align with magnetic fields, providing the basis for magnetic guidance when coupled with bacterial motility. This unique feature has inspired the concept of MTB as a self-propelled medical device to deliver therapeutic cargo. To this end, survival in physiological conditions and other microenvironments is essential. This study reveals the interplay between MTB physiology and magnetosome biomineralization subject to oxidative stress and varying environmental conditions, employing a holistic multi-parametric approach. Our results provide an in-depth understanding of the metabolic and physiological mechanisms at the single-cell level. This is crucial to develop more robust MTB biomanufacturing strategies to produce bacteria that possess the required quality attributes, thus paving the way for future biotechnological and biomedical application studies.