Conditional expression of Mycobacterium smegmatis ftsZ, an essential cell division gene.

To understand the role of Mycobacterium smegmatis ftsZ (ftsZ(smeg)) in the cell division process, the ftsZ gene was characterized at the genetic level. This study shows that ftsZ(smeg) is an essential gene in that it can only be disrupted in a merodiploid background carrying another functional copy. Expression of ftsZ(smeg) in M. smegmatis from a constitutively active mycobacterial promoter resulted in lethality whereas that from a chemically inducible acetamidase (ami) promoter led to FtsZ accumulation, filamentation and cell lysis. To further understand the roles of ftsZ in cell division a conditionally complementing ftsZ(smeg) mutant strain was constructed in which ftsZ expression is controlled by acetamide. Growth in the presence of 0.2 % acetamide increased FtsZ levels approximately 1.4-fold, but did not decrease viability or change cell length. Withdrawal of acetamide reduced FtsZ levels, decreased viability, increased cell length and eventually lysed the cells. Finally, it is shown that ftsZ(smeg) function in M. smegmatis can be replaced with the Mycobacterium tuberculosis counterpart, indicating that heterologous FtsZ(tb) can independently initiate the formation of Z-rings and catalyse the septation process. It is concluded that optimal levels of M. smegmatis FtsZ are required to sustain cell division and that the cell division initiation mechanisms are similar in mycobacteria.