Escherichia coli division inhibitor MinCD blocks septation by preventing Z-ring formation

The min system spatially regulates division through the topological regulat ion of MinCD, an inhibitor of cell division. MinCD was previously shown to inhibit division by preventing assembly of the Z ring however, this was que stioned in a recent report which indicated that MinCD acted after Z-ring fo rmation and prevented the recruitment of FtsA to the Z ring. This discrepan cy was due in part to alternative fixation conditions. We have therefore re investigated the action of MinCD and avoided fixation by using green fluore scent protein (GFP) fusions to division proteins. MinCD prevented the local ization of both FtsZ-GFP and ZipA-GFP, consistent with it preventing Z-ring assembly. Consistent with a direct interaction between FtsZ and the MinCD inhibitor, we find that increased FtsZ, but not FtsA, suppresses MinCD-indu ced lethality. Furthermore, strains carrying various alleles of ftsZ, selec ted on the basis of resistance to the inhibitor SuIA, displayed variable re sistance to MinCD. These results are consistent with FtsZ as the target of MinCD and confirm that this inhibitor prevents Z-ring assembly.