A dispensable role for forespore-specific gene expression in engulfment ofthe forespore during sporulation of Bacillus subtilis

During the stage of engulfment in the Bacillus subtilis spore formation pat hway, the larger mother cell engulfs the smaller forespore. We have tested the role of forespore-specific gene expression in engulfment using two sepa rate approaches. First, using an assay that unambiguously detects sporangia that have completed engulfment, we found that a mutant lacking the only fo respore-expressed engulfment protein identified thus far, SpoIIQ, is able t o efficiently complete engulfment under certain sporulation conditions. How ever, we have found that the mutant is defective, under all conditions, in the expression of the late-forespore-specific transcription factor sigma(G) ; thus, SpoIIQ is essential for spore production. Second, to determine if e ngulfment could proceed in the absence of forespore-specific gene expressio n, we made use of a strain in which activation of the mother cell-specific sigma factor sigma(E) was uncoupled from forespore-specific gene expression . Remarkably, engulfment occurred in the complete absence of sigma(F)-direc ted gene expression under the same conditions permissive for engulfment in the absence of SpoIIQ. Our results demonstrate that forespore-specific gene expression is not essential for engulfment, suggesting that the machinery used to move the membranes around the forespore is within the mother cell.