Requirement for the Cell Division Protein DivIB in Polar Cell Division and Engulfment during Sporulation inBacillus subtilis

Abstract

During spore formation in Bacillus subtilis, cell division occurs at the cell pole and is believed to require essentially the same division machinery as vegetative division. Intriguingly, although the cell division protein DivIB is not required for vegetative division at low temperatures, it is essential for efficient sporulation under these conditions. We show here that at low temperatures in the absence of DivIB, formation of the polar septum during sporulation is delayed and less efficient. Furthermore, the polar septa that are complete are abnormally thick, containing more peptidoglycan than a normal polar septum. These results show that DivIB is specifically required for the efficient and correct formation of a polar septum. This suggests that DivIB is required for the modification of sporulation septal peptidoglycan, raising the possibility that DivIB either regulates hydrolysis of polar septal peptidoglycan or is a hydrolase itself. We also show that, despite the significant number of completed polar septa that form in this mutant, it is unable to undergo engulfment. Instead, hydrolysis of the peptidoglycan within the polar septum, which occurs during the early stages of engulfment, is incomplete, producing a similar phenotype to that of mutants defective in the production of sporulation-specific septal peptidoglycan hydrolases. We propose a role for DivIB in sporulation-specific peptidoglycan remodelling or its regulation during polar septation and engulfment.

Evidence from Artificial Septal Targeting and Site-Directed Mutagenesis that Residues in the Extracytoplasmic β Domain of DivIB Mediate Its Interaction with the Divisomal Transpeptidase PBP 2B

“…This new model strongly implicates the DivIB/FtsL/DivIC complex in regulating the transpeptidase activity of PBP 2B. This hypothesis is consistent with, and strongly supported by, many previous observations, including the following: (i) these three proteins are absent from bacteria without cell walls (14); (ii) divIB null cells form an abnormally thick cell wall during sporulation in B. subtilis (35), suggesting that the peptidoglycan cross-linking activity of PBP 2B is aberrant; (iii) extragenic suppressors of a B. subtilis divIB null strain map to the extracytoplasmic noncatalytic domain of PBP 2B (5), which is thought to modulate PBP 2B activity; (iv) increased expression of divIB in B. subtilis reduces the requirement for MurB, one of the enzymes in the biosynthetic pathway used to synthesize the key peptidoglycan precursor, lipid II (29); (v) deletion of divIB in S. pneumoniae leads to increased sensitivity to ␤-lactam antibiotics (19), which function by inactivating the transpeptidase activity of FtsI/PBP 2B (and other penicillin binding proteins).…”

Staphylococcus aureus DivIBis a peptidoglycan‐binding protein that is required for a morphological checkpoint in cell division

“…In this study we have shown that the extracytoplasmic domain of S. aureus and B. subtilis DivIB binds peptidoglycan, and that both the α and γ domains are dispensable for this function. Although peptidoglycan hydrolase activity of DivIB has been previously suggested (Thompson et al ., ), no such enzymatic activity was detected in this present study (data not shown). Domain replacement studies have shown that the extracytoplasmic domain of B. subtilis DivIB, or the orthologous periplasmic domain of E. coli FtsQ, is essential for function (Buddelmeijer et al ., ; Katis and Wake, ; Chen et al ., ), suggesting that affinity for peptidoglycan may be important for DivIB function.…”

“…Interestingly, no DivIB orthologue is found in bacteria lacking cell walls, implying a role in peptidoglycan synthesis or remodelling (Margolin, ). Further evidence to support this has previously been reported; the inability of a B. subtilis divIB null mutant to sporulate results in a thickening of the polar septa, akin to mutants deficient in sporulation‐specific cell wall hydrolases (Thompson et al ., ). Additionally, coordinate expression of divIB and murB from the highly conserved dcw (division and cell wall) cluster, containing many genes involved in peptidoglycan biosynthesis and cell division, is necessary for growth and sporulation in B. subtilis (Real and Henriques, ).…”

The divisomal protein DivIB contains multiple epitopes that mediate its recruitment to incipient division sites

“…The absence of these proteins from bacteria without cell walls implies a role in the synthesis or remodelling of septal peptidoglycan. Consistent with this hypothesis, it was recently demonstrated that divIB null cells form a polar septum with a thicker cell wall than wild‐type cells during sporulation and fail to complete the forespore engulfment process (Thompson et al ., 2006). Intriguingly, however, there are several significant differences between DivIB and FtsQ.…”