Analysis of the role of prespore gene expression in the compartmentalization of mother cell-specific gene expression during sporulation of Bacillus subtilis

Abstract

A hallmark of sporulation of Bacillus subtilis is the formation of two distinct cells by an asymmetric division. The developmental programs in these two cells involve the compartmentalized activities of σ(E) in the larger mother cell and of σ(F) in the smaller prespore. Activation of σ(E) requires expression of the σ(F)-directed gene spoIIR. By immunofluorescence microscopy of a strain containing a spoIIR-lacZ fusion, we have shown that spoIIR is transcribed exclusively in the prespore. By placing spoIIR under the control of P(spoIIE), it was possible to express spoIIR before the spore septum was formed. Strains containing the P(spoIIE)-spoIIR construct activated σ(E) only in the mother cell in organisms that underwent the asymmetric sporulation division. Thus, compartmentalization of σ(E) activity did not require the compartmentalization of spoIIR expression. Nor did the compartmentalization of σ(E) require SpoIIAA, SpoIIAB, σ(F), or σ(E)- dependent transcription, all of which are required for prespore-specific gene expression. It is inferred that although σ(F) and σ(E) direct compartmentalized gene expression, neither of these σ factors, nor the genes under their control, directs the process of compartmentalization.