Sporulation is not limited to monoderms. A few species of diderm bacteria also form spores (some exospores and others endospores). The process is much the same as in monoderms, despite the different cell envelope structure. It begins with an asymmetric septum close to one pole of the cell, as you can see in this Acetonema longum. As in monoderms, the septum contains a thin layer of peptidoglycan (remember that diderms have a thin cell wall, though, so the thickness is about the same as in the rest of the cell). Note the array of densities lining the septal membrane on the right (facing the mother cell’s cytoplasm). This is likely a protein involved in making the spore coat.