STUDIES OF MAGNETOTACTIC BACTERIA BY SOFT X-RAY MICROSCOPY

Abstract

Magnetotactic bacteria (MTB) are ubiquitous in aquatic environments. They biomineralize membrane-bound magnetic nanoparticles (magnetosomes), which are magnetically single-domain, single crystals of either magnetite, Fe3O4, or greigite, Fe3S4. The chain is a strong magnetic dipole, which aligns the cell with the earth’s magnetic field (magnetotaxis) and, together with chemical signatures (aerotaxis), is believed to increase the efficiency of the organism in finding an optical oxygen concentration in the sediments. As the simplest organisms, in which biomineralization occurs, magnetotactic bacteria serve as an ideal model to study biomineralization mechanism. In this research, soft X-ray STXM (scanning transmission X-ray microscopy) was used to characterize the chemistry and magnetism of magnetotactic bacteria (MTB) on an individual cell and an individual magnetosome basis. Two types of MTB, Candidatus Magnetovibrio blakemorei strain MV-1 and multicellular magnetotoactic prokaryotes (MMPs) were studied in this project. In addition, ptychography technique, which does not rely on X-ray optics and holds promise for imaging with wavelength-limited resolution, is used to study biomineralization and magnetism of MTB cells. A spatial resolution of 7 nm below 1000 eV is achieved with ptychography, which is the highest in the soft X-ray region so far. Precursor-like and immature magnetosomes in intact MV-1 cells with ptychography are observed and a model for the pathway of magnetosome biomineralization for MV-1 is proposed. Our results demonstrate ptychography offers a superior means to characterize the chemical and magnetic properties of magnetotactic bacteria at the individual magnetosome level.