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

Abstract

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 horizontal bonding of peptidoglycan did not differ obviously among the three species. However, 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.

Caption of Graphical Abstract

This graphycal abstract shows peptidoglycan sacs isolated from two diderm bacteria. The boxed areas in the left panels are magnified as right panels. Myxococcus xanthus sac showed pore sizes larger than Escherichia coli ones. No directionality of pores against cell axis was detected as shown by FFT analysis shown in the right upper.