Correlative Fluorescence and Liquid Cell STEM of Live Magnetotactic Bacteria

Abstract

Magnetotactic bacteria, present in many natural aquatic environments, biomineralize ordered chains of uniform magnetite or greigite nanocrystals, also known as magnetosomes. These nanoparticles exhibit nearly perfect crystal structures, faceting, and consistent species-specific morphologies, leading to well-defined magnetic properties. As a result, magnetotactic bacteria can serve as a model system for the study of the molecular mechanisms for magnetite biomineralization. Transmission electron microscopy (TEM) can provide critical information about the organization of the magnetosomes, and provide critical information about the growth mechanisms by revealing the nanoparticle structure on the atomic level. Conventional TEM traditionally does not allow imaging in native liquid or atmospheric environments because of the high vacuum of the specimen enclosure. Even with advanced cryo-TEM imaging, it is inherently difficult to distinguish the individual components in bacterial specimens due to notoriously low contrast of a biological matter. Therefore direct observation of the time-dependent growth of magnetosomes is a significant challenge.