Swimming microorganisms often experience complex environments in their natural habitat. The same is true for microswimmers in envisioned biomedical applications. The simple aqueous conditions typically studied in the lab differ strongly from those found in these environments and often exclude the effects of small volume confinement or the influence that external fields have on their motion. In this work, we investigate magnetically steerable microswimmers, specifically magnetotactic bacteria, in strong spatial confinement and under the influence of an external magnetic field. We trap single cells in micrometer-sized microfluidic chambers and track and analyze their motion, which shows a variety of different trajectories, depending on the chamber size and the strength of the magnetic field. Combining these experimental observations with simulations using a variant of an active Brownian particle model, we explain the variety of trajectories by the interplay between the wall interactions and the magnetic torque. We also analyze the pronounced cell-to-cell heterogeneity, which makes single-cell tracking essential for an understanding of the motility patterns. In this way, our work establishes a basis for the analysis and prediction of microswimmer motility in more complex environments.

Recent breakthroughs in X-ray microscopy have enabled new means to investigate the structure and composition of materials ranging from energy-storage materials to individual cells to nanomaterials. [1][2][3][4][5] In particular, X-ray nanoprobe beamlines at synchrotron facilities provide sub-100 nm beam sizes in the hard X-ray energy regime (i.e., 5À30 keV) that enable investigations of the nanoscopic composition, structure, and organization of inorganic constituents in heterogeneous environments through an element-specific perspective. [6][7][8][9][10] The advantage of hard X-ray nanoprobes is the combination of imaging and spectroscopy, where each pixel or position on the sample contains spectral information at the nanoscale (e.g., X-ray fluorescence [XRF], X-ray absorption spectroscopy [XAS], X-ray diffraction, or scattering). Scanning X-ray fluorescence microscopy (SXFM) combined with such spectroscopy techniques has been highly advantageous for studying biological samples, revealing novel information on the intracellular biochemistry and role of metals in cells. [11] Such X-ray nanoprobe advancements have investigated intracellular elemental composition and structure of algae, [8,12,13] bacteria, [4] plants, [14] and even small animals. [15] Considering these milestones in nanoscale X-ray imaging of organisms, few studies

Swimming microorganisms often experience complex environments in their natural habitat. The same is true for microswimmers in envisioned biomedical applications. The simple aqueous conditions typically studied in the lab differ strongly from those found in these environments and often exclude the effects of small volume confinement or the influence that external fields have on their motion. In this work, we investigate magnetically steerable microswimmers, specifically magnetotactic bacteria, in strong spatial confinement and under the influence of an external magnetic field. We trap single cells in micrometer-sized microfluidic chambers and track and analyze their motion, which shows a variety of different trajectories, depending on the chamber size and the strength of the magnetic field. Combining these experimental observations with simulations using a variant of an active Brownian particle model, we explain the variety of trajectories by the interplay between the wall interactions and the magnetic torque. We also analyze the pronounced cell-to-cell heterogeneity, which makes single-cell tracking essential for an understanding of the motility patterns. In this way, our work establishes a basis for the analysis and prediction of microswimmer motility in more complex environments.

<p>This report demonstrates how scanning X-ray fluorescence microscopy (SXFM) and nanoscale X-ray absorption near-edge structure (nano-XANES) can spatially and chemically identify intracellular iron species at the single-cell level, creating an opportunity to examine the role of iron storage in magnetite biomineralization. Fe K-edge nano-XANES measurements of <i>Magnetospirillum gryphiswaldense</i> in varied iron media conditions and iron storage capacity revealed intracellular iron heterogeneities through a distinction between formed magnetosomes and intracellular iron material. This work highlights the potential of nano-XANES in providing an experimental advantage in the multidisciplinary field of biomineralization.</p>

<p>This report demonstrates how scanning X-ray fluorescence microscopy (SXFM) and nanoscale X-ray absorption near-edge structure (nano-XANES) can spatially and chemically identify intracellular iron species at the single-cell level, creating an opportunity to examine the role of iron storage in magnetite biomineralization. Fe K-edge nano-XANES measurements of <i>Magnetospirillum gryphiswaldense</i> in varied iron media conditions and iron storage capacity revealed intracellular iron heterogeneities through a distinction between formed magnetosomes and intracellular iron material. This work highlights the potential of nano-XANES in providing an experimental advantage in the multidisciplinary field of biomineralization.</p>