The Balance between Activity of Two Different Peptidoglycan (PG) Insertion Machineries and Alterations in the Molecular Properties of PG Could Contribute to Changes in Cell Width. (A) The Rod system inserts lateral wall material and is known to promote rod-like growth at a fixed width. Recently, it was shown that bifunctional penicillin-binding proteins (PBPs) insert material independent of the Rod system. It is thus possible that, while the Rod system promotes constrained lateral insertion, the bifunctional PBPs promote unconstrained, or expansive insertion. In this way, simply by tuning the relative activities of these different systems based on the surface area to volume ratio (SA/V) requirements, cells could flexibly alter their width. (B) A variety of different molecular alterations to the PG network could lead to changes in the overall cell width over time.