X-ray microscopy and imaging of Escherichia coli, LPS and DNA

Application of X-ray microscopy in analysis of living hydrated cells

Because there is a limit for analysis of fine hydrophilic cell structures of living cells in medium by ordinary techniques, including electron microscopy, the development of a new technology to overcome such limitation is highly desirable. In this regard, soft X-ray microscopy (high-resolution X-ray imaging of structures), which does not require any special procedures for sample preparation, has been developed and applied to analyze structures of biological specimens. In this article, application of two types of X-ray microscopes, which use laser-produced plasma X-rays or synchrotron radiation to image the structure of macrophage cells, is introduced as an example of a novel approach to analysis of biological specimens. Both types of X-ray microscopy show the network of fine fibrillar surface structures on macrophages in medium. Ordinary transmission and scanning electron microscopy and light microscopy also show the presence of such structures, but electron microscopy showed alterations due to sample processing and light microscopy did not show a clear image due to low resolution. Thus, X-ray microscopy has the potential capability to analyze structures of live cells in a hydrated condition and may reveal a function-related structural alignment of cells in their natural form.

Direct visualization of gram-negative bacterial lipopolysaccharide self-assembly

Bacterial lipopolysaccharides (LPS) are outer cell wall components of gram-negative bacteria that may cause septic shock in mammals. The exact morphology of LPS when interacting with macromolecular complexes of the septic shock pathway in blood is still uncertain. Here, the geometry and morphology of hydrated bacterial LPS, dispersed in solution, at and below its the critical aggregate concentration, were directly examined by tapping mode atomic force microscopy (TMAFM) and dynamic light scattering. High-resolution phase-shift TMAFM images of hydrated LPS of Salmonella minnesota Re595, Salmonella typhimurium, and Escherichia coli 0111:B4 adsorbed on mica surfaces unveiled nanosized lipidic particles with a species-specific organization. The complex hydrodynamic geometry exhibited by LPS in dilute suspensions may have consequences for the interpretation of LPS biological activity in the host immune response.