Characterization of the cell division proteins, MreC and DivIVA of Bacillus subtilis

The mre genes of B. subtilis are associated with cell shape determination. It was reported that the MreB is essential for cell viability. However, very little is known about the roles of MreC and MreD in cell shape determination. When the B. subtilis MreB protein, or the MreC and MreD proteins, were expressed in E. coli, these expressions resulted in a rod to sphere morphological shift.;To investigate the role of MreC in cell shape determination, a strain in which MreC expression is under control of an inducible promoter was created. The morphological changes of cells lacking MreC were examined by scanning and transmission electron microscopy. It was shown that MreC is essential for viability of B. subtilis, and that reduction in MreC levels resulted in morphological changes from rods to swellen and twisted cells, followed by cell lysis. Accumulation of peptidoglycan-like polymeric material at one side of the division septum of the cells was observed. These results suggested that the MreC protein is involved in the control of septal versus long axis peptidoglycan synthesis.;The domain of the MreC protein responsible for septal localization was examined by the construction of C- or N-terminus deletions of MreC, which were fused with GFP. Results from this study suggested that both C- and N-terminus domains are necessary for septal localization.;In B. subtilis, the process by which a septum is formed at the midcell site is regulated by the Min and DivIVA system. Immunofluorescence microscopy and GFP-fusion analysis were performed to examine the localization of the division proteins such as DivIVA, FtsZ, and MinC. All division proteins were localized at the potential division sites in the wild-type cells. Although FtsZ and DivIVA were not dependent upon MinCD for their localization, DivIVA and FtsZ were codependent for septal ring localization. Internal deletions of the DiviVA protein were created to further define the domain of DivIVA responsible for septal localization. Deletion of nucleotides 196--263 and 196--397 of the open reading frame produced proteins which failed to properly localize.