SPOIIE MUTANTS OF BACILLUS-SUBTILIS COMPRISE 2 DISTINCT PHENOTYPIC CLASSES CONSISTENT WITH A DUAL FUNCTIONAL-ROLE FOR THE SPOIIE PROTEIN

Mutations in the spoIIE locus of Bacillus subtilis block sporulation a t the stage of asymmetric septation and prevent compartment-specific a ctivation of the transcription factor sigma(F). Recent ultrastructural studies of spoIIE mutants led to the conclusion that cells blocked at the stage of asymmetric septation form primarily thick septal structu res similar to those formed at the mid-cell site during vegetative gro wth, although in an earlier study Piggot (J. Bacteriol. 114:1241-1253, 1973) clearly detected a more complex range of phenotypes. We have ex amined the phenotypes of six spoIIE mutants, including one example of the previously studied null type, spoIIE21. We confirmed that the spoI IE21 mutant and two other null mutants exhibit the classic thick-septu m phenotype. However, two of the missense mutants, the spoIIE64 and sp oIIE71 mutants, were found to display a strikingly different phenotype characterized by the presence of only thin asymmetric septa, frequent ly at both polar positions, as noted by Piggot. This phenotype is esse ntially identical to those of spolIA (sigma(F)) and spoIIG (sigma(E)) null mutants, which also form sporulation septa that appear structural ly normal at the level of electron microscopy. Despite tile formation of apparently normal asymmetric septa, spolIE64 and spoIIE71 mutants a re fully defective in activation of sigma(F)-dependcnt gene expression . These results Indicate that the functional roles performed by SpoIIE in septum assembly and sigma factor regulation are distinct and separ able.