Structure of a unit of surface area of the sacculus of E. coli and B Structure of a unit of surface area of the sacculus of E. coli and B. subtillis. Structure of a unit of surface area of the sacculus of E. coli and B. subtillis. While the structure of the tessera is correct, the rectilinear arrangement, although typical of the presentation in textbooks, is certainly wrong. It would be correct if a murein fabric had been synthesized under stress-free conditions in the absence of the organisms. However, since the forces acting on the sacculus when it is an integral part of a functioning wall surface protecting the cell would stress it in six directions, it would become distorted to become hexagonal (see Fig. 6). Arthur L. Koch Clin. Microbiol. Rev. 2003; doi:10.1128/CMR.16.4.673-687.2003