SPOLLQ, A FORESPORE-EXPRESSED GENE REQUIRED FOR ENGULFMENT IN BACILLUS-SUBTILIS

A crucial step in converting an actively growing Bacillus subtilis cel l into a dormant spore is the formation of a cell within a cell. This unusual structure is created by a phagocytosis-like process in which t he larger mother cell progressively engulfs the adjacent smaller fores pore. Only mutations blocking engulfment at an early stage and affecti ng genes expressed in the mother cell have been identified. Here we de scribe a new locus, spollQ, which is transcribed in the forespore and which encodes a membrane-bound protein required at a late stage of eng ulfment. Immunofluorescence microscopy analysis have shown that SpollQ is initially targeted to the septum at the boundary between the two c ells and then spreads around the entire membrane of the forespore. Sep tum targeting requires only the first 52 residues of SpollQ as well as unidentified forespore-specific components. Electron-microscopy studi es of cells engineered to activate the mother-cell program of gene exp ression independently of the forespore indicate that other as yet unch aracterized genes are involved in engulfment and that this morphologic al process is driven from both sides of the forespore envelope.