Visualization of peptidoglycan layer isolated from gliding diderm bacteria, Flavobacterium johnsoniae and Myxococcus xanthus, by quick-freeze deep-etch replica electron microscopy

The bacterial peptidoglycan layer plays an important role in protecting the bacteria from turgor pressure, viruses, and predators. However, it also acts as a barrier in transmitting forces generated on the cell membrane to adhesion proteins on the surface during gliding locomotion. In this study, peptidoglycan layers were isolated from two species of gliding diderm, i.e., Gram-negative bacteria, and their structures were visualized by quick-freeze deep-etch replica electron microscopy. The diameter of pores in the peptidoglycan layer of M. xanthus and the area of surface pores were 51 nm and 14.6%, respectively, which were significantly larger than those of E. coli (32 nm and 5.8%) and F. johnsoniae (29 nm and 7.0%). Based on this, we discussed the mechanism by which diderm bacteria transmit forces across the PG layer to the bacterial surface. SignificancePeptidoglycan is a rigid meshwork that protects bacterial cells from turgor stress, virus, and predators. Bacteria move to get nutrients and escape from predators. The force for motility is generated in the cell membrane and transmitted to the surface across the peptidoglycan layer. In this study, the peptidoglycan structures of two representative gliding Gram-negative bacteria were visualized to understand the transmission mechanism.