Our initial goal was to determine if FtsZ was sufficient to generate a contractile force in vivo. Our working hypothesis was that, if FtsZ was sufficient we should see deformations of the inner membrane when only FtsZ and its membrane tethers FtsA23 and ZipA24 (aka the proto-ring) are present at midcell (but PG synthesizing enzymes are not). We cryogenically preserved Escherichia coli cells expressing a chromosomal copy of FtsZ-GFP by vitrification and imaged them by cryo-CLEM (Supplementary Fig.
