[ODP-065] Visualization of peptidoglycan in diderm bacteria by quick-freeze and deep-etch electron microscopy
The whole architecture of peptidoglycan is not easy to visualize because of its low density and the flexibility. Quick-freeze and deep-etching (QFDE) electron microscopy is a method in which a specimen is fixed by quick-freezing, and coated by metal, and the metal layer is observed by transmission electron microscopy. This method is useful to visualize the peptidoglycan. Previously, we observed peptidoglycan of Bacillus subtilis, which is classified into monoderm (gram-positive) bacteria, and visualized the fiber structure on the surface and the disruption process by QFDE.In the present study, we visualized the peptidoglycan layer of Escherichia coli, Flavobacterium johnsoniae and Myxococcus xanthus, which are classified into diderm (gram-negative) bacteria. The peptidoglycan layer was isolated as a sacculus by SDS boiling or protease treatment. In E. coli and F. johnsoniae, mesh-like holes of 10 to 30 nm2 were observed in peptidoglycan sacks isolated by SDS boiling followed by protease treatment, although not in the sacculi isolated without protease treatments. In M. xanthus, sacculi showed mesh structures of various sizes up to 100 nm2 even without protease treatments. Interestingly, they showed holes of approximately 100 nm2 at both cell pole areas. The structural differences peptidoglycan may be linked to cell flexibility and slime secretion of M. xanthus.