Role of penicillin-binding protein PBP2B in assembly and functioning of the division machinery of Bacillus subtilis

We have characterized the role of the penicillin-binding protein PBP 2B in cell division of Bacillus subtilis. We have shown that depletion of the pro tein results in an arrest in division, but that this arrest is slow, probab ly because the protein is relatively stable. PBP 2B-depleted filaments cont ained, at about their mid-points, structures resembling partially formed se pta, into which most, if not all, of the division proteins had assembled. A lthough clearly deficient in wall material, membrane invagination seemed to continue, indicating that membrane and wall ingrowth can be uncoupled. At other potential division sites along the filaments, no visible ingrowths we re observed, although FtsZ rings assembled at regular intervals. Thus, PBP 2B is apparently required for both the initiation of division and continued septal ingrowth. Immunofluorescence microscopy showed that the protein is recruited to the division site. The pattern of localization suggested that this recruitment occurs continually during septal ingrowth. During sporulat ion, PBP 2B was present transiently in the asymmetrical septum of sporulati ng cells, and its availability may play a role in the regulation of sporula tion septation.