Characterization of the essential cell division gene ftsL(yIID) of Bacillus subtilis and its role in the assembly of the division apparatus.

We have identified the Bacillus subtilis homologue of the essential cell division gene, ftsL, of Escherichia coli. Repression of ftsL in a strain engineered to carry a conditional promoter results in cell filamentation, with a near immediate arrest of cell division. The filaments show no sign of invagination, indicating that division is blocked at an early stage. FtsL is also shown to be required for septation during sporulation, and depletion of FtsL blocks the activation but not the synthesis of the prespore-specific sigma factor, sigmaF. Immunofluorescence microscopy shows that depletion of FtsL has little or no effect on FtsZ ring formation, but the assembly of other division proteins, DivIB and DivIC, at the site of division is prevented. Repression of FtsL also results in a rapid loss of DivIC protein, indicating that DivIC stability is dependent on the presence of FtsL, in turn suggesting that FtsL is intrinsically unstable. The instability of one or more components of the division apparatus may be important for the cyclic assembly/disassembly of the division apparatus.