Nanomechanical probing of the septum and surrounding substances on Streptococcus mutans cells and biofilms

We report a unique bio-nanomechanical behavior at the septum (Z-ring) of Streptococcus mutans-containing biofilm through in situ measurements obtained by atomic force microscopy. A distinct serrated pattern on the releasing force–displacement curves can only be observed with the use of a sharp nanosized probe tip, and this was found at the septum of S. mutans. Further investigations suggested the serrated patterns could be due to the unfolding of some sub-surface divisome proteins. Seismometer measurements were conducted at the septum by placing an ultra-sensitive atomic force microscope probe on the surface. Unique periodic vibrations were observed at the septum under various biofilm conditions. This finding suggests the possibility of remodeling of the cell wall nanostructure at the septum of S. mutans.